Asymmetric Profile Research Articles

Long-term Simultaneous Monitoring Observations of SiO and H2O Masers toward the Mira Variable WX Serpentis

We present the results from long-term simultaneous monitoring observations of SiO and H2O masers toward the Mira variable star WX Serpentis. This study has been conducted with 21 m single-dish radio telescopes of the Korean VLBI Network from 2009 June to 2021 June. Five maser lines were considered: SiO v = 1, 2, J = 1−0; SiO v = 1, J = 2−1, 3−2; and H2O 61,6–52,3 transitions, with the SiO maser lines distributed near the stellar velocity and the H2O maser exhibiting an asymmetric line profile with five to six peaked components. Intense H2O maser emissions suddenly appeared in 2019 September, indicating flaring. The intensity variations of SiO and H2O masers are strongly correlated with the optical light curve (OLC) of the central star, with individual phase lags; the phase lag of the H2O maser relative to the OLC is larger than that of the SiO masers. The consequent phase difference between the SiO masers and the H2O maser likely indicates that their formation regions and main driving mechanisms are different from each other. The SiO masers in WX Ser exhibit a dominant single-peak velocity distribution, similar to other Mira variable stars. However, the H2O maser displays distinct morphological features, showing a radial acceleration and preferential intensity dominance at blueshifted velocities. This suggests that the H2O maser clouds of WX Ser are moving outward, thereby developing an asymmetric outflow owing to nonuniform material ejection from the stellar atmosphere. The findings confirm that an initial asymmetric outflow structure emerged during the thermally pulsing asymptotic giant branch phase, specifically in the Mira variable star stage.

Tailored microstructure in laser-based powder bed fusion of IN718 through novel beam shaping technology

Inconel 718, processed by Laser-based Powder Bed Fusion of Metals (PBF-LB/M), exhibits epitaxial dendrite growth, leading to an anisotropic columnar microstructure. While columnar microstructures offer creep resistance, equiaxed microstructures provide more balanced mechanical properties. Understanding how to tailor the as-built microstructure in the PBF-LB/M process remains a persistent challenge. Recent advancements in beam shaping offer solutions for customizing heat flow direction in the PBF-LB/M process and tailoring the as-built microstructure. This research aims to systematically study how the laser beam shape affects anisotropy in the as-built microstructure and tensile mechanical properties. By using an inverse calculated beam shape, called as chair-shaped, the texture strength represented by J-index was reduced from 4.6 (generated by a ring-shaped beam profile with the same beam intensity and laser process parameters) to 1.37. The study prioritizes high productivity, with a building rate of 16 mm3/s (80 μm layer thickness) across chosen process parameters compared to state-of-the-art with a build rate of 4.2 mm3/s (40 μm layer thickness). The findings indicate that rotational asymmetric laser beam profiles with a relative beam diameter of 400 μm significantly enhance productivity by broadening the process window. These profiles also have a profound impact on the microstructure and tensile properties compared to ring-shaped and core-ring laser beam profiles. The new microstructure features a notable reduction in grain size, elongation, and texture index, producing mechanical properties that are comparable to those of an isotropic microstructure.

An Antagonistic Photovoltaic Memristor for Bioinspired Active Contrast Adaptation.

Machine vision systems that consist of cameras and image-processing components for visual inspection and identification tasks play a critical role in various intelligent applications, including pilotless vehicles and surveillance systems. However, current systems usually possess a limited dynamic range and fixed photoresponsivity, restricting their capability of gaining high-fidelity images when encoding a high-contrast scene. Here, it is shown that a photovoltaic memristor incorporating two antagonistic photovoltaic junctions can autonomously adjust its response to varying light stimuli, enabling the amplification of shadows and inhibition of highlight saturation. Due to the dynamic photodoping effect at the p-n junction with an asymmetrical profile, the photocurrent polarities of the antagonistic memristor can be changed as the light intensity increases. The light-intensity-dependent switchable photovoltaic behaviors match Weber's law where photosensitivity is inversely proportional to the light stimuli. An 11×11 memristor array is used to detect a high-contrast scene with light intensities ranging from 1 to 5×104 µW cm-2, achieving a similar active contrast adaptation performance compared with the human visual systems (less than 1.2 s at 94 dB). This work paves the way for innovative neuromorphic device designs and may lead to the development of state-of-the-art active visual adaptation photosensors.

ExoplaNeT accRetion mOnitoring sPectroscopic surveY (ENTROPY)

Context. Accretion among planetary mass companions is a poorly understood phenomenon, due to the lack of both observational and theoretical studies. The detection of emission lines from accreting gas giants facilitates detailed investigations into this process. Aims. This work presents a detailed analysis of Balmer lines from one of the few known young, planetary-mass objects with observed emission, the isolated L2γ dwarf 2MASS J11151597+1937266 with a mass between 7 and 21 MJup and an age of 5–45 Myr, located at 45 ± 2 pc. Methods. We obtained the first high-resolution (R ~ 50 000) spectrum of the target with VLT/UVES, an echelle spectrograph operating in the near-ultraviolet to visible wavelengths (3200–6800 Å). Results. We report several resolved hydrogen (H I; H3–H6) and helium (He I; λ5875.6) emission lines in the spectrum. Based on the asymmetric line profiles of Hα and Hβ, the 10% width of Hα (199 ± 1 km s−1), tentative He I λ6678 emission, and indications of a disk from mid-infrared excess, we confirm ongoing accretion at this object. Using the Gaia update of the parallax, we revise its temperature to 1816 ± 63 K and radius to 1.5 ± 0.1 RJup. Analysis of observed H I profiles using a 1D planet-surface shock model implies a pre-shock gas velocity, v0 = 120−40+ 80 km s−1, and a pre-shock density, log(n0/cm−3) = 14−5+ 0. The pre-shock velocity points to a mass, Mp = 6−4+ 8 MJup, for the target. Combining H I line luminosities (Lline) and planetary Lline−Lacc (accretion luminosity) scaling relations, we derived a mass accretion rate, Ṁacc = 1.4−0.9+ 2.8 × 10−8 MJup yr−1. Conclusions. The line-emitting area predicted from the planet-surface shock model is very small (~0.03%), and points to a shock at the base of a magnetospherically induced funnel. The Hα profile exhibits a much stronger flux than predicted by the model that best fits the rest of the H I profiles, indicating that another mechanism than shock emission contributes to the Hα emission. Comparison of line fluxes and Ṁacc from archival moderate-resolution SDSS spectra indicate variable accretion at 2MASS J11151597+1937266.

Tunable phonon-photon coupling induces double MMIT and enhances slow light in an atom-opto-magnomechanics

Abstract In this paper, we theoretically investigate the magnomechanically induced transparency phenomenon, Fano resonance, and the slow/fast light effect in the situation where an atomic ensemble is placed inside the hybrid cavity of an opto-magnomechanical system. The system is driven by dual optical and phononic drives. We show double magnomechanically induced transparency (MMIT) in the probe output spectrum by exploiting the phonon-photon coupling strength. Then, we study the effects of the decay rate of the cavity and the atomic ensemble on magnomechanically induced transparency. In addition, we demonstrate that effective detuning of the cavity field frequency changes the transparency window from a symmetrical to an asymmetrical profile, resembling Fano resonances. Further, the fast and slow light effects in the system are explored. Besides, we show that the slow light profile is enhanced by adjusting the phonon-photon coupling strength. This result may have potential applications in quantum information processing and communication.

Enhanced pointing and charge properties of electron beams from few-TW laser wakefield acceleration with an asymmetric density profile in a sub-millimeter nitrogen gas jet

This work demonstrates the feasibility of creating a sub-millimeter, subsonic nitrogen gas jet using a 178-μm diameter orifice to conduct laser wakefield acceleration (LWFA) with 1-TW, 40-fs laser pulses. More importantly, our findings reveal that using a blade to impede part of the gas flow and create an asymmetric density profile with a shortened down-ramp leads to a notable reduction in pointing fluctuations and an increase in the total charge of the output electron beams. As evidenced by the corresponding particle-in-cell simulation, the laser intensity is more effectively sustained toward the downstream end of the shaped gas jet, allowing for effective excitation of low-amplitude plasma waves that help preserve the accelerated electrons over the target rear side. In contrast, the pulse intensity drops significantly within the rear side of the unshaped gas jet, resulting in continuously diminishing plasma waves and decreased beam charge. The steeper gradient of the density down-ramp in the shaped gas jet also leads to a more rapid increase in the plasma wavelength over a reduced propagation distance, which helps mitigate the dephasing of accelerated electrons and increase the charge at the high-energy side of the spectrum. Our study paves the way for the future development of few-TW LWFA using a subsonic gas jet with sharp edges to further enhance the properties of output electron beams.

Investigating instabilities in magnetized low-pressure capacitively coupled RF plasma using particle-in-cell (PIC) simulations

The effect of a uniform magnetic field on particle transport in low-pressure radio frequency (RF) capacitively coupled plasma (CCP) has been studied using a particle-in-cell model. Three distinct regimes of plasma behavior can be identified as a function of the magnetic field. In the first regime at low magnetic fields, asymmetric plasma profiles are observed within the CCP chamber due to the effect of E→×B→ drift. As the magnetic field increases, instabilities develop and form self-organized spoke-shaped structures that are distinctly seen within the bulk plasma closer to the sheath. In this second regime, the spoke-shaped coherent structures rotate inside the plasma chamber in the −E→×B→ direction, where E→ and B→ are the DC electric and magnetic field vectors, respectively, and the DC electric field exists in the sheath and pre-sheath regions. The spoke rotation frequency is in the megahertz range. As the magnetic field strength increases further, the rotating coherent spokes continue to exist near the sheath. The coherent structures are, however, accompanied by new small-scale incoherent structures originating and moving within the bulk plasma region away from the sheath. This is the third regime of plasma behavior. The threshold values of the magnetic field between these regimes were found not to vary with changing plasma reactor geometry (e.g., area ratio between ground and powered electrodes) or the use of an external capacitor between the RF-powered electrode and the RF source. The threshold values of the magnetic field between these regimes shift toward higher values with increasing gas pressure. Analysis of the results indicates that the rotating structures are due to the lower hybrid instability driven by density gradients and electron-neutral collisions. This paper provides guidance on the upper limit of the magnetic field for instability-free operation in low-pressure CCP-based semiconductor deposition and etch systems that use the external magnetic field for plasma uniformity control.

Investigation of Vertical-axis Tidal Turbine Mechanical Strength using FSI Analysis based on Blade Profile

Abstract Tidal energy, as a renewable energy source harnessed from the ocean, holds substantial promise owing to its heightened energy density, reliability, and longevity. An investigation encompassing the deployment of tidal stream electricity from 2003 through August 2020 revealed that blade malfunction was identified as the primary reason for system failures, with generator and monitoring system failures occurring subsequently. The majority of the research that has been done on the design of vertical-axis tidal turbine blades has focused on how well the blade performs in terms of power output without taking into account the generation of mechanical force. This force can potentially shorten the blade’s lifetime when implemented in a real-world scenario. By modelling a steady-state fluid-structure interaction (FSI) configuration, this study examines how the shape of the turbine blades affects the amount of mechanical force they generate, particularly in vertical-axis tidal turbines. The type of blade profile is the variable under consideration, and the stress levels experienced by a structure are influenced by the type of blade profile used. When comparing symmetrical and asymmetrical NACA straight blade types under similar climatic conditions, it has been found that the blade profile plays a significant role. Asymmetrical blade profiles, in particular, generate a higher lift force compared to symmetrical ones, thereby affecting stress levels more noticeably.

SN 2021adxl: A luminous nearby interacting supernova in an extremely low-metallicity environment

SN 2021adxl is a slowly evolving, luminous, Type IIn supernova with asymmetric emission line profiles, similar to the well-studied SN 2010jl. We present extensive optical, near-ultraviolet, and near-infrared photometry and spectroscopy covering ∼1.5 years post discovery. SN 2021adxl occurred in an unusual environment, atop a vigorously star-forming region that is offset from its host galaxy core. The appearance of Lyα and O II, as well as the compact core, would classify the host of SN 2021adxl as a “Blueberry” galaxy, analogous to higher redshift, low-metallicity, star-forming dwarf “Green Pea” galaxies. Using several abundance indicators, we find a metallicity of the explosion environment of only ∼0.1 Z⊙, the lowest reported metallicity for a Type IIn SN environment. SN 2021adxl reaches a peak magnitude of Mr ≈ −20.2 mag and since discovery, SN 2021adxl has faded by only ∼4 magnitudes in the r band with a cumulative radiated energy of ∼1.5 × 1050 erg over 18 months. SN 2021adxl shows strong signs of interaction with a complex circumstellar medium, seen by the detection of X-rays, revealed by the detection of coronal emission lines, and through multi-component hydrogen and helium profiles. In order to further understand this interaction, we model the Hα profile using a Monte Carlo electron scattering code. The blueshifted high-velocity component is consistent with emission from a radially thin spherical shell resulting in the broad emission components due to electron scattering. Using the velocity evolution of this emitting shell, we find that the SN ejecta collide with circumstellar material of at least ∼5 M⊙ assuming a steady-state mass-loss rate of ∼4 − 6 × 10−3 M⊙ yr−1 for the first ∼200 days of evolution. SN 2021adxl was last observed to be slowly declining at ∼0.01 mag d−1, and if this trend continues, SN 2021adxl will remain observable after its current solar conjunction. Continuing the observations of SN 2021adxl may reveal signatures of dust formation or an infrared excess, similar to that seen for SN 2010jl.

TIC 290061484: A Triply Eclipsing Triple System with the Shortest Known Outer Period of 24.5 Days

We have discovered a triply eclipsing triple-star system, TIC 290061484, with the shortest known outer period, P out, of only 24.5 days. This “eclipses” the previous record set by λ Tauri at 33.02 days, which held for 68 yr. The inner binary, with an orbital period of P in = 1.8 days, produces primary and secondary eclipses and exhibits prominent eclipse timing variations with the same periodicity as the outer orbit. The tertiary star eclipses, and is eclipsed by, the inner binary with pronounced asymmetric profiles. The inclinations of both orbits evolve on observable timescales such that the third-body eclipses exhibit dramatic depth variations in TESS data. A photodynamical model provides a complete solution for all orbital and physical parameters of the triple system, showing that the three stars have masses of 6.85, 6.11, and 7.90 M ⊙, radii near those corresponding to the main sequence, and T eff in the range of 21,000–23,700 K. Remarkably, the model shows that the triple is in fact a subsystem of a hierarchical 2+1+1 quadruple with a distant fourth star. The outermost star has a period of ∼3200 days and a mass comparable to the stars in the inner triple. In ∼20 Myr, all three components of the triple subsystem will merge, undergo a Type II supernova explosion, and leave a single remnant neutron star. At the time of writing, TIC 290061484 is the most compact triple system and one of the tighter known compact triples (i.e., P out/P in = 13.7).

A Precessing Stellar Disk Model for Superorbital Modulations of the Gamma-Ray Binary LS I+61° 303

Gamma-ray binary LS I+61° 303 consists of a neutron star orbiting around a Be star with a period of P orb ≃ 26.5 days. Apart from orbital modulations, the binary shows long-term flux variations with a superorbital period of Psup≃4.6yr as seen in nearly all wavelengths. The origin of this superorbital modulation is still not well understood. Under the pulsar wind–stellar outflow interaction scenario, we propose that the superorbital modulations of LS I+61° 303 could be caused by the precession of the Be disk. Assuming X-rays arise from synchrotron radiation of the intrabinary shock, we develop an analytical model to calculate expected flux modulations over the orbital and superorbital phases. The asymmetric two-peak profiles in orbital light curves and sinusoidal-like long-term modulations are reproduced under the precessing disk scenario. The observed orbital phase drifting of the X-ray peak and our fitting of long-term X-ray data indicate that the neutron star is likely orbiting around the star with a small eccentricity and periastron phase around Φp ∼ 0.6. We compare the Corbet diagrams of LS I+61° 303 with other Be/X-ray binaries, and the linear correlation in the Psup–Porb diagram suggests that the precession of the Be disk in LS I+61° 303 is induced by the tidal torque of its neutron star companion.

Mathematical model and generation analysis for crossed helical gear system

Purpose Crossed helical gears have point contact and their surfaces are subject to high surface stress. Contact stress and root tooth stress are the most common sources of failure in crossed helical gear. This paper aims to study the load-carrying capacity and performance of crossed helical gear teeth with different gear tooth profiles. To overcome defects and reduce the sensitivity to small shaft angle changes. The combined tooth profile is designed to reduce the bending stresses, contact stresses and tooth deflection, and prevent pinion failure in the gearbox. Design/methodology/approach The principle of the method is a line contact is introduced instead of a point contact between two teeth in mesh with each other. The tooth surface of the helical gear is designed and cut by a modified tool. Higher normal pressure angles like 25° and 35° are used. The modified involute is accomplished to eliminate interference between the teeth. Engineering software packages have been applied to generate all crossed helical gears gear profiles. The modification is compounding curves consisting of an epicycloid-involute-hypocycloid gear teeth profile generated by the cutter modified. Findings The stresses in the crossed helical gear teeth profile were reduced by increasing the normal pressure angle values. Using a 35° pressure angle the enhancement percentage in contact stress and teeth fillet region will be about 29.345% and 15.421%, respectively. The best enhancement in a gear’s resistance is the epicycloid-involute-hypocycloid gear teeth profile. The enhancement was 32.610% and 18.588%. The skew in line of action in skewed helical gear will be sensitive when the crossing angles are small. Their teeth surface tends to be easily worn out; however, the wearing process will be reduced by using a proposed gear teeth profile. Practical implications The gear teeth to be modified are cut by a shaper process. The modifying rack cutter of this study can be used as a reference for creating a different helical gears sample. The helical teeth surface is modified to become an envelope of the other. This makes an original point contact change into a line contact. The epicycloid-involute-hypocycloid gear teeth profile is preferred for a higher contact ratio and a large load capacity. This work explicitly introduces a new method of kinematic consideration to improve the load capacity of crossed helical gear. Originality/value This paper showed some novel results by the unique shape of the rack-cutter designed to generate different helical angles and different gear positions. In the future, it will make valuable contributions to the further development of the dynamic performance of a crossed helical gear system through the study in the field of using asymmetric teeth profiles of helical gears with tip relief as the manner to enhance the crossed helical gear performance. Investigation of crossed helical gear by applying a predesigned parabolic function of transmission error enables the absorption of linear discontinuous functions caused by misalignment.

Multiwavelength study of on-disk coronal-hole jets with IRIS and SDO observations

Context. Solar jets are an important field of study, as they may contribute to the mass and energy transfer from the lower to the upper atmosphere. Aims. We use the Interface Region Imaging Spectrograph (IRIS) and Solar Dynamic Observatory (SDO) observations to study two small-scale jets (jet 1 and jet 2) originating in the same on-disk coronal hole observed in October 2013. Methods. We combine dopplergrams, intensity maps, and line width maps derived from IRIS Si IV 1393.755 Å spectra along with images from the Atmospheric Imaging Assembly (AIA) on SDO to describe the dynamics of the jets. Images from AIA, with the use of the emission measure loci technique and rectangular differential emission measure (DEM) distributions, provide estimations of the plasma temperatures. We used the O IV 1399.77 Å, 1401.16 Å spectral lines from IRIS to derive electron densities. Results. For jet 1, the SDO images show a small mini-filament 2 minutes before the jet eruption, while jet 2 originates at a pre-existing coronal bright point. The analysis of asymmetric spectral profiles of the Si IV 1393.755 Å and 1402.770 Å lines reveals the existence of two spectral components at both regions. One of the components can be related to the background plasma emission originating outside the jet, while the secondary component represents higher-energy plasma flows associated with the jets. Both jets exhibit high densities of the order of 1011 cm−3 at their base and 1010 cm−3 at the spire, respectively, as well as similar average nonthermal velocities of ∼50–60 km/s. However, the two jets show differences in their length, duration, and plane-of-sky velocity. Finally, the DEM analysis reveals that both jets exhibit multithermal distributions. Conclusions. This work presents a comprehensive description of the thermal parameters and the dynamic evolution of two jets. The locations of the asymmetric profiles possibly indicate the areas of energy release triggering the jets.

Praseodymium doped ceria: A new sight on coupled thermo-mechanical properties and oxygen vacancy diffusion via statistical moment approach

Applications of praseodymium doped ceria (PDC) in solid oxide fuel cells require a deep insight into the thermal expansion, stresses, and ionic conduction. Nonetheless, the investigation of thermo-mechanical properties and oxygen vacancy diffusion remains incomplete. Based on free Helmholtz energy, we formulate analytical expressions to directly connect thermal expansion coefficient, elastic moduli, oxygen vacancy–dopant binding and oxygen vacancy migration energies by employing statistical moment method (SMM). The SMM calculations capture the full anharmonicity of lattice thermal vibrations. Our analyses report the significant influences of temperature and dopant content on the thermal expansion coefficient, bulk and Young’s moduli, oxygen vacancy–dopant binding and oxygen vacancy migration energies, and ionic conductivity. The role of Pr dopant on the oxygen vacancy diffusion is fully described by combining the symmetric energy profiles related to blocking effect and asymmetric energy profiles generated from trapping effect. By switching van der Waals (vdW) forces on and off in the SMM calculations, we first show that the vdW forces cause a positive effect on the mechanical properties but reduce the thermal expansion and resist the oxygen vacancy diffusion. Our findings are discussed concerning the results from other calculations and experiments in the literature. The insights on the thermo-mechanical properties and oxygen vacancy diffusion for PDC crystal can be generalized and applied to other ceramic materials that are essential for solid state batteries.

The impact of relaxation on isothermal acoustic traveling waves: A new solvable model based on Navier–Stokes–Maxwell theory

An analysis of isothermal acoustic traveling waves in a particular sub-class of Maxwell fluids, specifically, those which behave like perfect gases and wherein the shear viscosity is proportional to the square of the mass density, is presented. Exact solutions are derived and analyzed, shock thickness results are computed, and the thermodynamic consistency of the isothermal assumption is verified vis-à-vis the Mach number values considered. It is shown that, within the range where both yield dispersed shock profiles, the Maxwell case leads to significantly smaller shock thicknesses and more asymmetric solution profiles than those admitted by the corresponding Newtonian (fluid) case.

Atomic-Level Free Energy Landscape Reveals Cooperative Symport Mechanism of Melibiose Transporter.

The Major Facilitator Superfamily (MFS) transporters are an essential class of secondary active transporters involved in various physiological and pathological processes. The melibiose permease (MelB), which catalyzes the stoichiometric symport of the disaccharide melibiose and monovalent cations (e.g., Na+, H+, or Li+), is a key model for understanding the cation-coupled symport mechanisms. Extensive experimental data has established that positive cooperativity between the cargo melibiose and the coupling cation is central to the symport mechanism. However, the structural and energetic origins of this cooperativity remain unclear at the atomistic level for MelB and most other coupled transporters. Here, leveraging recently resolved structures in inward- and outward-facing conformations, we employed the string method and replica-exchange umbrella sampling simulation techniques to comprehensively map the all-atom free energy landscapes of the Na+-coupled melibiose translocation across the MelB in Salmonella enterica serovar Typhimurium (MelBSt), in comparison with the facilitated melibiose transport in a uniporter mutant. The simulation results unravel asymmetrical free energy profiles of melibiose translocation, which is tightly coupled to protein conformational changes in both the N- and C-terminal domains. Notably, the cytoplasmic release of the melibiose induces the simultaneous opening of an inner gate, resulting in a high-energy state of the system. Periplasmic sugar binding and cytoplasmic melibiose released are dynamically coupled with changes in the internal gating elements along the translocation pathway. The outward-facing sugar-bound state is thermodynamically most stable, while the occluded state is a transient state. The binding of Na+ facilitates melibiose translocation by increasing the melibiose-binding affinity and decreasing the overall free energy barrier and change. The cooperative binding of the two substrates results from the allosteric coupling between their binding sites instead of direct electrostatic interaction. These findings add substantial new atomic-level details into how Na+ binding facilitates melibiose translocation and deepen the fundamental understanding of the molecular basis underlying the symport mechanism of cation-coupled transporters.

Nanostructured aramid fiber/Cu/BN composite Janus films with broadband electromagnetic interference shielding and superior thermally conductive/electrically insulating performance

Modern electronic technology necessitates the development of composite materials with effective electromagnetic protection. This work presents a novel strategy constructing an aramid nanofiber (ANF)-based Janus film (ANF@Cu-ANF/BN) using an electroless plating-vacuum assisted filtration-pressing technique. The film exhibits an unique asymmetric property profile, with one side being electrically conductive and thermally conductive/electrically insulating on the other. Exceptional EMI shielding effectiveness of 105.22 and 106.96 dB is obtained in the 8.2–12.4 GHz and 26.5–40 GHz ranges, respectively. In addition, the film demonstrates an impressive out-of-plane thermal conductivity of 2.703 W/(m·K). suggesting superior thermal management capabilities when integrated into heat sinks for high-power light-emitting diode modules. In terms of mechanical robustness, the film possesses a tensile strength of 14.31 MPa. The ANF@Cu-ANF/BN Janus composite films effectively harmonize electromagnetic shielding, thermal conductivity, and mechanical integrity, offering an innovative pathway of developing advanced materials that fulfill the stringent requirements of modern electronic devices.

A Chimera method for thermal part-scale metal additive manufacturing simulation

This paper presents a Chimera approach for the thermal problems in welding and metallic Additive Manufacturing (AM). In particular, a moving mesh is attached to the moving heat source while a fixed background mesh covers the rest of the computational domain. The thermal field of the moving mesh is solved in the heat source reference frame. The chosen framework to couple the solutions on both meshes is a non-overlapping Domain Decomposition (DD) with Neumann–Dirichlet transmission conditions.Increased steadiness and accuracy within the vicinity of the Heat Affected Zone (HAZ) are the main advantages of this approach. The steadiness gain allows for the use of larger time steps, which is vital in AM applications and, in particular, Laser Powder Bed Fusion (LPBF), where the disparity of time scales represents a major hurdle. Moreover, enhanced accuracy can be observed in the resulting morphology of the melt pool. It will be shown that the method addresses classical shortcomings pointed out by Goldak without requiring the use of an asymmetrical heat source profile.

Quantitative piezoelectric measurements of partially released Pb(Zr, Ti)O3 structures

The effective large signal longitudinal piezoelectric coefficient (d33,f∗) of piezoelectric thin films on rigid substrates has been widely investigated. Unclamped piezoelectric thin films are predicted to have a higher d33,f∗ coefficient due to reduced constraints on piezoelectric strain, domain reorientation, and domain wall motion, but quantitative measurements of this coefficient have been limited. This study uses microfabrication techniques along with double-beam laser interferometry (DBLI) to accurately determine the longitudinal piezoelectric coefficient of Pb(Zr,Ti)O3 thin films in partially released piezomicroelectromechanical structures. A two-step backside release process was used: first, deep reactive ion etching to create backside vias and second, wet etching of the ZnO sacrificial layer to release the area beneath the Pb(Zr,Ti)O3 thin films. Post wet etching, optical profilometry showed concavely deformed diaphragms resulting from asymmetrical stress profiles through the diaphragm thickness. DBLI was then used to examine diaphragm deflection under an applied unipolar voltage ranging from 0 to 10 V. Devices with 50% and 75% of the area beneath the top electrode released exhibited large signal d33,f∗ values of 410 ± 6 and 420 ± 8 pm/V, respectively, more than three times higher than the d33,f∗ value of the clamped samples: 126 ± 13 pm/V. The reasons contributing to the large d33,f∗ include (i) the change in stress levels due to the release process, (ii) the elimination of mechanical constraints from substrate clamping, and (iii) enhanced domain reorientation. These findings confirm that substrate declamping significantly boosts the piezoelectric coefficient, bringing d33,f∗ closer to the bulk longitudinal piezoelectric coefficient (d33).

Interfacial inhomogeneous plastic deformation during rotary friction welding of dissimilar AA2219-SS321 joint combination with AA6061 interlayer

This research investigates the inherent radial non-uniformity within the rotary friction welding process, particularly concerning microstructure attributes like grain size, grain boundaries, misorientation angles, and interlayer presence along the radial axis. SS321-AA2219 rotary friction welding was carried out with and without an AA6061 interlayer. The numerical thermal model suggests increase in temperatures from the center to the periphery, due to non-uniform heat generation. Also, dissimilar material across the interface resulted in an asymmetric temperature profile along axial direction. Plastic deformation on the Aluminum side suggests dynamic recrystallization and grain refinement, whereas pronounced low-angle grain boundary (LAGB) formation near the SS side interface validates dynamic recovery. A radial non-uniformity in microstructure is observed, with metrics such as average grain size, LAGB fraction, and misorientation showing an increase from the center towards the periphery. The insertion of an interlayer alters process dynamics, manifesting in reduced temperatures and heightened forces, resulting in a more consolidated joint by enhancing the strength by 31 %. Interdiffusion of elements across the interface formed Fe-Al intermetallic compounds (IMC) confirmed with X ray diffraction. Fractography analysis elucidates the presence of rubbing marks and facet surfaces in interlayer-less joints, while joints with interlayer display sticking and dimples.