bluuebunny/crossref_metadata_2025 huggingface dataset:
Transformations to the aluminum coordination environment and network polymerization in amorphous aluminosilicates under pressure
Authors: Gammond Lawrence V. D. , Zeidler Anita , Youngman Randall E. , Fischer Henry E. , Bull Craig L. , Salmon Philip S.
Published: August 2024

The structure of calcium aluminosilicate glasses (CaO)x(Al2O3)y(SiO2)1−x−y with the near tectosilicate compositions x ≃ 0.19 and 1 − x − y ≃ 0.61 or x ≃ 0.26 and 1 − x − y ≃ 0.49 was investigated by in situ high-pressure neutron diffraction and 27Al nuclear magnetic resonance (NMR) spectroscopy. The results show three distinct pressure regimes for the transformation of the aluminum coordination environment from tetrahedral to octahedral, which map onto the deformations observed in the production of permanently densified materials. The oxygen packing fraction serves as a marker for signaling a change to the coordination number of the network forming motifs. For a wide variety of permanently densified aluminosilicates, the aluminum speciation shares a common dependence on the reduced density ρ′ = ρ/ρ0, where ρ is the density and ρ0 is its value for the uncompressed material. The observed increase in the Al–O coordination number with ρ′ originates primarily from the formation of six-coordinated aluminum Al(VI) species, the fraction of which increases rapidly beyond a threshold ρthr′∼ 1.1. The findings are combined to produce a self-consistent model for pressure-induced structural change. Provided the glass network is depolymerized, one-coordinated non-bridging oxygen atoms are consumed to produce two-coordinated bridging oxygen atoms, thus increasing the network connectivity in accordance with the results from 17O NMR experiments. Otherwise, three-coordinated oxygen atoms or triclusters appear, and their fraction is quantified by reference to the mean coordination number of the silicon plus aluminum species. The impact of treating Al(VI) as a network modifier is discussed.
Influence of chemical substitution and sintering temperature on the structural, magnetic, and magnetocaloric properties of La1−xSrxMn1−yFeyO3
Authors: Brahiti N. , Balli M. , Eskandari M. Abbasi , El Boukili A. , Fournier P.
Published: August 2024

The effects of sintering temperature (Ts) and chemical substitution on the structural and magnetic properties of manganite compounds La1−xSrxMn1−yFeyO3(0.025≤x≤0.7;y=0.01,0.15) are explored in a search to optimize their magnetocaloric properties around room temperature. A ferromagnetic (FM) to paramagnetic (PM) phase transition is observed at a Curie temperature Tc that can be controlled to approach room temperature by Sr and Fe substitution, but also by adjusting the sintering temperature Ts. Accordingly, the magnetic entropy change (−ΔSM) quantifying the magnetocaloric effect (MCE) presents a peak at or close to Tc that shifts and broadens with both Sr and Fe doping and is further tuned with sintering temperature. Altogether, we show that it is possible to adjust the strength and dominance of the ferromagnetic coupling in these ceramics, but also using disorder as a tool to broaden and adjust the temperature range with a significant magnetic entropy change.
Spacing effect on aerodynamic characteristics for a rail-cum-road bridge with twin asymmetrical parallel girders
Authors: Zou Yunfeng , Yang Changgan , He Xuhui , Liu Lulu , Yang Jiafeng
Published: August 2024

Due to the asymmetrical cross section of long-span rail-cum-road twin-girder bridges, the aerodynamic interference effect and flow characteristics of the twin girders in the gap are complicated. To study the influence of spacing on their aerodynamic characteristics, section model wind tunnel tests were conducted on a long-span rail-cum-road twin-girder cable-stayed bridge. This study considered the two conditions of bare and completed girders and the two inflow directions of 0° and 180°, with a spacing ratio range of L/Br = 0.1–2.0, and tested the surface wind pressures of the twin girders. Their aerodynamic and flow characteristics were analyzed, and the influence of spacing on their aerodynamic interference was clarified. The results show that for asymmetrical twin girders, the spacing and direction of incoming flow are still the key factors affecting their wind pressure distribution and flow characteristics. Due to the asymmetry of twin-girder sections, the influence of spacing on the wind pressure distribution and flow pattern varies with different flow directions. Furthermore, the attachments to completed girders enhance the asymmetry, making the aerodynamic and flow characteristics more complex than those of bare girders. Finally, three flow patterns are summarized: the upstream girder lower surface wake acts on the downstream girder fairing lower surface, acts on its fairing upper surface, and acts at its fairing.
Effect of interparticle and inter-cluster dipole–dipole interactions on dynamic behavior of superparamagnetic iron oxide nanoparticles modified with citric acid
Authors: Muliawan W. , Okubo K. , Kitamoto Y.
Published: August 2024

This paper describes the hydrodynamic behavior of superparamagnetic iron oxide nanoparticles modified with citric acid (CA-SPIONs) in suspension under alternating current magnetic fields given interparticle and inter-cluster dipole–dipole interactions. The cluster size of the CA-SPIONs is modulated to control interparticle interactions, and the ionic concentration of the CA-SPION suspension is varied to control inter-cluster interactions. Dynamic magnetic susceptibility (DMS) measurements of the CA-SPION suspensions under alternating current magnetic fields indicate that the interparticle interaction by clustering and the inter-cluster interaction by increasing the ionic concentration cause frequency spectra modulation, such as their broadening in the low-frequency region and a decrease in the Brownian relaxation frequency. The experimentally obtained DMS spectra differ from the spectra numerically calculated from the hydrodynamic size distribution of CA-SPIONs using the Debye relaxation model without considering the magnetic interactions; the differences are attributed to the interparticle and inter-cluster dipole–dipole interactions. These insights contribute to a deeper understanding of dynamics of superparamagnetic iron oxide nanoparticles and facilitate nanoparticle parameter optimization for tailored applications in the biomedical field, particularly for their efficacy and precision in liquid-phase biosensing and imaging.
Experimental study on the effects of the throat heights of the air annular slot on the rotating detonation waves
Authors: Zhao Minghao , Wang Zhicheng , Wang Ke , Fan Wei
Published: August 2024

In order to investigate the effects of the throat heights of the air annular slot on the rotating detonation waves, experiments have been carried out while varying the throat height of the air annular slot (i.e., 0.5, 1.5, 2.5, and 4.0 mm), the mass flow rate of oxidizer (35–300 g/s), and the equivalence ratio (0.15–1.8). Air and ethylene have been utilized as oxidizer and fuel, respectively. The experimental results indicate that rotating detonation waves can be obtained under different inflow conditions, and two operating phenomena were observed, i.e., the detonation cases (the single-wave mode and the oscillation mode) and the deflagration cases (the deflagration mode and the chaotic mode). The effects of the throat height on the operating range of stable rotating detonations are related to the minimum mass flow rate of oxidizer. As the throat height increases, the minimum mass flow rate of oxidizer also increases. Furthermore, the relationship between the minimum Mach number to obtain rotating detonations at each throat height and the throat height has been obtained. Moreover, the effects of the eccentricity ratio of the air annular slot on the propagation modes have also been demonstrated.
Lattice Boltzmann method/computational fluid dynamics-discrete element method applications for transport and packing of non-spherical particles during geo-energy explorations: A review
Authors: Fan Dian , Hou Huilin , Zeng Junsheng , Yuan Bin , Lv Zhuojian , Chen Yaoming , Li Yue , Huang Siyuan , Striolo Alberto , Zhang Dongxiao
Published: August 2024

Understanding the behavior of dispersed particles in subsurface porous media is essential for studying many transport phenomena in geo-energy exploration. Relevant phenomena include fluid transport through rock matrices, undesirable production of formation sands, colloid migration, circulation of drilling cuttings, and displacement of proppants in hydraulic fractures. The discrete element method (DEM), when coupled with the lattice Boltzmann method (LBM) and computational fluid dynamics (CFD), represents a useful numerical approach to studying these microscopic processes. This integrated approach allows for detailed modeling of particle–fluid and particle–particle interactions, which is particularly useful in dealing with particles with non-spherical shapes. This review focuses on recent advancements in DEM implementations for such particles and their coupling schemes with LBM and CFD numerical tools. It aims to assist scholars and practitioners in selecting the most effective LBM/CFD-DEM strategy for studying particle transport and packing in geo-energy scenarios. Although tailored for geophysical flows, the methodologies and analytical frameworks presented here also apply to fundamental investigations of particle-laden flows.
Mid-infrared silicon photonics: From benchtop to real-world applications
Authors: Mitchell Colin J. , Hu Tianhui , Sun Shiyu , Stirling Callum J. , Nedeljkovic Milos , Peacock Anna C. , Reed Graham T. , Mashanovich Goran Z. , Rowe David J.
Published: August 2024

Silicon photonics is one of the most dynamic fields within photonics, and it has seen huge progress in the last 20 years, addressing applications in data centers, autonomous cars, and sensing. It is mostly focused on the telecommunications wavelength range (1.3 and 1.55 µm), where silicon becomes transparent. In this range, there are excellent light sources and photodetectors, as well as optical fibers operating with extremely low losses and dispersion. It is a technology that hugely benefits from the availability of complementary metal–oxide–semiconductor (CMOS) fabrication infrastructure and techniques used for microelectronics. Silicon and germanium, as another CMOS compatible group IV material, are transparent beyond the wavelength of 2 µm. The mid-IR wavelength range (2–20 µm) is of particular importance as it contains strong absorption signatures of many molecules. Therefore, Si- and Ge-based platforms open up the possibility of small and cost-effective sensing in the fingerprint region for medical and environmental monitoring. In this paper, we discuss the current mid-IR silicon photonics landscape, future directions, and potential applications of the field.
Thermal transport in graphene under large mechanical strains
Authors: Wang Yingtao , Zhang Xian
Published: August 2024

Flexible electronic devices with skin-like properties are hailed as revolutionary for the development of next-generation electronic devices, such as electric-skin and humanoid robotics. Graphene is intrinsically flexible due to its structural thinness in nature and are considered next-generation materials for wearable electronics. These devices usually experience a large mechanical deformation in use so as to achieve intimate conformal contact with human skin and to coordinate complex human motions, while heat dissipation has been a major limitation when the device is under a large mechanical strain. Unlike the small deformation (<1%) induced by intrinsic material factors such as lattice mismatch between material components in devices, a large mechanical deformation (>1%) by an external loading condition could lead to apparent changes to global geometric shapes and significantly impact thermal transport. In this study, we investigated the thermal conductivities of graphene under several large mechanical strains: 2.9%, 4.3%, and 6.1%. We used a refined opto-thermal Raman technique to characterize the thermal transport properties and discovered the thermal conductivities to be 2092 ± 502, 972 ± 87, 348 ± 52, and 97 ± 13 W/(m K) for the relaxed state, 2.9%, 4.3%, and 6.1% tensile strain, respectively. Our results showed a significant decreasing trend in thermal conductivities with an increasing mechanical strain. The findings in this study reveal new thermal transport mechanisms in 2D materials and shed light on building novel flexible nanoelectronic devices with enhanced thermal management.
Numerical study of the formation of vortex rings with reversed rotation in viscoelastic liquids
Authors: Yuan Chenguang , Xu Duo
Published: August 2024

Laminar vortex rings in viscoelastic liquids display distinct characteristics compared to the Newtonian counterparts. One interesting scenario is that the core of a vortex ring rotates reversely (in contrast to the Newtonian counterpart), termed as the “negative vortex ring.” This phenomenon was initially observed experimentally by Palacios-Morales et al. [“Negative vortices: The formation of vortex rings with reversed rotation in viscoelastic liquids,” Phys. Fluids 27, 051703 (2015)]. In this study, we numerically investigate the formation of the negative vortex rings through controlling the polymer viscosity ratios, Weissenberg numbers, and Reynolds numbers. In the simulations, we indeed observe the formation of negative vortex rings. In the examination of the effects of flow parameters, both the shear thinning and viscoelastic effects of the fluids are found to be necessary for the formation, while the flow inertia suppresses the formation. The concurrent existence of high shear and low extensional viscosities in flow fields seems to be a critical condition for the formation.
Feasible suggestions of scale-adaptive simulation approach based on the high-fidelity large-eddy simulation of supersonic turbulent boundary layer
Authors: Wang Bin , Xu Chang-Yue , Lin Xiao-Hui , Wang Zhe , Liu Wei-Hua
Published: August 2024

Large-eddy simulation (LES) of the Navier–Stokes equations is carried out to investigate the supersonic turbulent boundary layer (STBL) developing over a flat plate at free-stream Mach number M∞=2.0 and Reynolds number Reδ≈ 13 500. The seventh-order weighted essentially non-oscillatory (WENO-7) scheme is adopted to ensure calculation accuracy. To demonstrate the credibility of the proposed improvements, a posteriori test is conducted. Other LES-like methods are also adopted for comparison. The validation results show that WENO-LES can provide credible predictions when grid resolution is sufficient. Thus, current LES results can be regarded as a reliable database for further analysis. The distributions of flow topologies and turbulent statistics are obtained after time average operation. A preliminary conclusion can be drawn that the position y+≈ 14 in buffer layer may be the appropriate interface for Reynolds-averaged Navier–Stokes (RANS) and LES computations of LES-like methods in STBL. Diverse length scales in LES-like methods are calculated based on high-fidelity flow fields. On this basis, a blending function is added to the original von Karman length formula. A dissipation-adaptive length scale is proposed for the scale-adaptive simulation (SAS) method. A comparison of the original SAS and delayed-DES (DDES) methods reveals that the improved method exhibits grid-independent characteristics of RANS/LES interface. Furthermore, the coherent vortical structures and flow visualization of the a posteriori test indicate that the improved method has a satisfactory ability to promote the generation of small-scale structures and to capture turbulent fluctuations.
Device-level XPS analysis for physical and electrical characterization of oxide-channel thin-film transistors
Authors: Cho Yun-Ju , Kwon Young-Ha , Seong Nak-Jin , Choi Kyu-Jeong , Lee Myung Keun , Kim Gyungtae , Yoon Sung-Min
Published: August 2024

This work aims to validate the feasibility of device-level analysis to reflect the effects of fabrication processes and operations, as contrasted with the conventional method of x-ray photoelectron spectroscopy (XPS), which is widely employed in amorphous oxide semiconductor thin-film transistors (TFTs) but analyzes film-level specimens. First, an analysis setup was introduced to determine the optimal x-ray target position for device-level XPS, where the intensity of channel components is maximized, through imaging XPS. Then, to demonstrate the effectiveness of this approach, the impact of channel composition and bias-stress was investigated through the implementation of device-level XPS on bottom-gate InGaZnO TFTs. The cationic composition ratios of the fabricated TFTs varied from 0.27:1:1.33 (In:Ga:Zn) and 0.28:1:2.21 when the subcycle of the Zn precursor increased by a factor of 1.5 in the atomic-layer deposition process. The device with a higher Zn ratio exhibited a more negative turn-on voltage and a twice larger subthreshold swing. These characteristics were validated from the comparisons in the relative amount of oxygen vacancies in O 1s of the channel and interface regions by 8.4%p and 5.6%p, respectively, between the devices. Furthermore, the electron trapping effect was verified for the devices subjected to a positive gate bias-stress of 3 MV/cm, as evidenced by the changes in the binding energy difference (0.35 eV) between the channel and gate insulator layers, in comparison to the non-stressed device. Consequently, this work demonstrates that device-level XPS can be an effective tool for understanding TFTs' characteristics in various ways beyond film-level analysis.
The self-annealing of irradiation induced defects in magnetite Fe3O4: Revealing reversible irradiation-induced disorder transformation through in situ TEM
Authors: Lopez Morales Angelica M. , Chen Wei-Ying , Kaoumi Djamel
Published: August 2024

This work reports heavy ion-irradiation effects in polycrystalline Fe3O4. For this matter, Fe/Fe3O4 heterostructures were irradiated in situ in a transmission electron microscopy with 1 MeV Kr ions at 50 K. Evidence of cubic to monoclinic transformation (a.k.a Verwey transition) was recorded in some magnetite grains upon cooling the sample (around 90 K); however, most of the oxide grains retain their cubic spinel structure. Irradiation effects were analyzed in the cubic phase up to a maximum dose of 38 dpa without the sign of amorphization. The extinction of first-order reflections was recorded at doses below 1 dpa, indicating the formation of a new (metastable) phase with half of the lattice parameters compared to the unirradiated Fe3O4 crystal. The formation of the new crystalline phase, which also presents a high resistance to amorphization, is related to the disordering of the cation lattice and the high mobility of the cation interstitials. The metastable phase readily recovers around 225 K during the natural warming of the sample from 50 K to room temperature.
Estimate of force noise from electrostatic patch potentials in LISA Pathfinder
Authors: Vitale S , Ferroni V , Sala L , Weber W J
Published: August 2024

This paper discusses force noise in LISA and LISA Pathfinder arising from the interaction of patch potentials on the test mass and surrounding electrode housing surfaces with their own temporal fluctuations. We aim to estimate the contribution of this phenomenon to the force noise detected in LISA Pathfinder in excess of the background from Brownian motion. We introduce a model that approximates the interacting test mass and housing surfaces as concentric spheres, treating patch potentials as isotropic stochastic Gaussian processes on the surface of these spheres. We find that a scenario of patches due to surface contamination, with diffusion driven density fluctuations, could indeed produce force noise with the observed frequency f
−2 dependence. However, there is not enough experimental evidence, neither from LISA Pathfinder itself, nor from other experiments, to predict the amplitude of such a noise, which could range from completely negligible to explaining the entire noise excess. We briefly discuss several measures to ensure that this noise is sufficiently small in LISA.
Analysis of the monotonicity method for an anisotropic scatterer with a conductive boundary
Authors: Harris Isaac , Hughes Victor , Lee Heejin
Published: August 2024

In this paper, we consider the inverse scattering problem associated with an anisotropic medium with a conductive boundary. We will assume that the corresponding far–field pattern is known/measured and we consider two inverse problems. First, we show that the far–field data uniquely determines the boundary coefficient. Next, since it is known that anisotropic coefficients are not uniquely determined by this data we will develop a qualitative method to recover the scatterer. To this end, we study the so–called monotonicity method applied to this inverse shape problem. This method has recently been applied to some inverse scattering problems but this is the first time it has been applied to an anisotropic scatterer. This method allows one to recover the scatterer by considering the eigenvalues of an operator associated with the far–field operator. We present some simple numerical reconstructions to illustrate our theory in two dimensions. For our reconstructions, we need to compute the adjoint of the Herglotz wave function as an operator mapping into H
1 of a small ball.
Recent advances in the mechanism, properties, and applications of hafnia ferroelectric tunnel junctions
Authors: Lim Eunjin , Kim Dahye , Park Jongmin , Koo Minsuk , Kim Sungjun
Published: August 2024

The increasing demand of information and communication technology has pushed conventional computing paradigm to its limit. In addition, physical and technological factors have constrained the advancement of conventional memory devices. Considering the rapid back-and-forth transfer of a large amount of information, emerging memory should demonstrate space efficiency, fast speed, and low-cost requirements. Accordingly, ferroelectric films based on HfO
x
are being intensively researched owing to their high energy efficiency and compatibility with complementary metal oxide semiconductor. Particularly, owing to the simplicity of their structure, low power, and less variation, hafnia-based ferroelectric tunnel junctions (FTJs) stand out among ferroelectric memories. Numerous studies have demonstrated the improved ferroelectricity of FTJs using various engineering methods, including doping, annealing, and varying electrodes. To improve the properties of HfO
x
-based FTJs and enhance their applications, it is necessary to organize and discuss recent studies and prospects. Therefore, this paper reviews in-depth and comprehensive studies on FTJs and their advantages compared to other emerging devices. Additionally, in-memory computing applications, outlook, and challenges of hafnia-based FTJs are presented.
Electrochemical studies and diffusion kinetics in the Chevrel phase (Mo6S8) for rechargeable Mg batteries
Authors: Gupta Gazal , Gupta Raghvendra , Gupta Amit , Kumar Deepak
Published: August 2024

Based on its availability, cost and stability, rechargeable Mg batteries (RMBs) are potential candidates to fulfill the futuristic demand for high energy density storage devices. However, they are minimally explored due to sluggish Mg ion diffusion in cathode materials. Literature suggests that the Chevrel phase (CP) (Mo6S8) holds promise as a cathode (positive electrode) for RMBs due to its open structure and self-healing properties during cycling. This study reports the electrochemical performance of Mo6S8 (synthesized using cost effective precursors (Cu–Mo–MoS2)) as a cathode for RMBs for the first time. The development of Mo6S8 is a two-step process: (i) synthesis of Cu2Mo6S8 via high energy milling method using Cu, Mo and MoS2 as precursors and (ii) leaching of Cu from Cu2Mo6S8. The morphological and structural characteristics of the developed materials are recorded using x-ray diffraction and field emission scanning electron microscopy. The developed Mo6S8 is cuboid-shaped with a rhombohedral unit cell. To record the electrochemical performance of Mo6S8 as a positive electrode for rechargeable Mg batteries (RMBs), CR2016 type half-cells are fabricated. It is observed that the initial discharge capacity was 89 mA h g−1 at a current density of 25 mA g−1 (1C = 128 mA g−1). Interestingly, the capacity increases from 89 to ≈100 mA h g−1 during 50 cycles which is higher than reported in the literature. The coulombic efficiency (CE) of ≈90% is observed for 100 cycles. Additionally, the over-potential decreases with an increase in cycle number. Importantly, the authors explained the diffusion behavior of Mg ions in Mo6S8 with 0.4 M 2(PhMgCl)-AlCl3/THF (APC) electrolyte via cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic intermittent titration (GITT) technique. The diffusion coefficients have been calculated and fall in the range of 10−8−10−14 cm2 s−1. Also, the authors explain the effect of outer site activation during cycling on the diffusion kinetics of the materials using the GITT technique. This investigation of diffusion kinetics of Mg ions in Mo6S8 may pave the way for evaluating various CPs as electrode materials for future rechargeable magnesium battery systems.
Advancing high thermal conductivity: novel theories, innovative materials, and applications in thermal management technologies
Authors: Ouyang Yulou , Zhang Zhongwei
Published: August 2024

Effective thermal management is crucial for the performance and stability of modern electronics, emphasizing the demand for high thermal conductivity (

κ

). This review summarizes the latest development in high

κ

, discussing the emerging theories, innovative materials and practical applications for interfacial heat dissipation. Unique phononic thermal transport behaviors are discussed, including four phonon–phonon scattering, hydrodynamic phonons, surface phonon-polaritons, and more. The review also highlights innovative materials with high

κ

, such as two-dimensional pentagonal structures, boron carbon nitrogen structures, hexagonal boron arsenide and θ-phase tantalum nitride. In addition, the potential of polymer composites reinforced with high

κ

fillers and surface engineering for advanced electronic applications are also discussed. By integrating these theoretical approaches and material innovations, this review offers comprehensive strategies for enhancing thermal management in modern electronic devices.
Ship Radiated Noise Signal Denoising Method With SVMD-AAPE-RPE-CC-AWTD
Authors: Lu Binjie , Zhang Xiaobing , DAI Zhonghua , Yuan Peilong
Published: August 2024

To solve the denoising problem of ship radiated noise signal (SRNSs), a method based on successive variational mode decomposition (SVMD), amplitude-aware permutation entropy (AAPE), reverse permutation entropy (RPE), correlation coefficient (CC) and adaptive wavelet thresholding denoising (AWTD) algorithm, named SVMD-AAPE-RPE-CC-AWTD, is proposed. The algorithm integrates intrinsic mode functions (IMFs) decomposition, IMFs classification, IMFs denoising and reconstruction, and is designed in an integrated manner. In IMFs decomposition, SVMD is introduced to decompose the signal into several IMFs, which select the number of adaptive decomposition levels without the need for manual parameter presetting. In IMFs classification, AAPE and RPE are introduced to adaptively adjust the entropy threshold to discriminate between signal IMFs and non-signal IMFs. By calculating the CC between the non-signal IMFs and the original signal, the noisy IMFs and noise IMFs are further distinguished. In terms of IMFs denoising and reconstruction, an ATWD algorithm is designed based on the optimal wavelet selection method to adaptively select appropriate wavelet basis and decomposition levels, and the improved threshold selection and threshold function are introduced. Finally, comparison tests of denoising simulated signals and the measured SRNS are designed to verify the effectiveness and superiority of the proposed method.
Surface pressure reconstruction from LPT data with boundary conforming grids
Authors: Cakir Bora O , Gonzalez Saiz Gabriel , Sciacchitano Andrea
Published: August 2024

The coupling between fluid-structure interactions is governed by the pressure distribution over the interaction surface between the fluid and solid domains. The capabilities of non-intrusive optical techniques, such as particle image velocimetry and Lagrangian particle tracking (LPT), have been proven to provide accurate velocity and acceleration information within the flow field while simultaneously tracking the corresponding structural deformations. However, scattered data from LPT measurements are typically mapped onto Cartesian grids, independently of the shape of the solid objects in the measurement domain. The use of Cartesian grids poses challenges for the determination of the surface pressure because the velocity gradients close to the object’s surface are not captured accurately. Therefore, an alternative surface pressure reconstruction scheme utilizing LPT data based on the arbitrary Lagrangian–Eulerian approach is proposed to mitigate the error propagation associated with the use of uniform grids. The introduced method provides an exact surface conformation utilizing boundary fitted coordinate systems and radial basis function based mesh deformations, which eliminates the need to use extrapolations to obtain surface pressure distributions. The introduced approach is assessed by means of a synthetic hill surface probing a three-dimensional analytical flow field; its practical applicability is demonstrated through an experimental characterization of turbulent boundary layer interactions with a steadily and unsteadily deforming elastic membrane.
Noise-imitation learning: unpaired speckle noise reduction for optical coherence tomography
Authors: Yao Bin , Jin Lujia , Hu Jiakui , Liu Yuzhao , Yan Yuepeng , Li Qing , Lu Yanye
Published: August 2024

Objective. Optical coherence tomography (OCT) is widely used in clinical practice for its non-invasive, high-resolution imaging capabilities. However, speckle noise inherent to its low coherence principle can degrade image quality and compromise diagnostic accuracy. While deep learning methods have shown promise in reducing speckle noise, obtaining well-registered image pairs remains challenging, leading to the development of unpaired methods. Despite their potential, existing unpaired methods suffer from redundancy in network structures or interaction mechanisms. Therefore, a more streamlined method for unpaired OCT denoising is essential. Approach. In this work, we propose a novel unpaired method for OCT image denoising, referred to as noise-imitation learning (NIL). NIL comprises three primary modules: the noise extraction module, which extracts noise features by denoising noisy images; the noise imitation module, which synthesizes noisy images and generates fake clean images; and the adversarial learning module, which differentiates between real and fake clean images through adversarial training. The complexity of NIL is significantly lower than that of previous unpaired methods, utilizing only one generator and one discriminator for training. Main results. By efficiently fusing unpaired images and employing adversarial training, NIL can extract more speckle noise information to enhance denoising performance. Building on NIL, we propose an OCT image denoising pipeline, NIL-NAFNet. This pipeline achieved PSNR, SSIM, and RMSE values of 31.27 dB, 0.865, and 7.00, respectively, on the PKU37 dataset. Extensive experiments suggest that our method outperforms state-of-the-art unpaired methods both qualitatively and quantitatively. Significance. These findings indicate that the proposed NIL is a simple yet effective method for unpaired OCT speckle noise reduction. The OCT denoising pipeline based on NIL demonstrates exceptional performance and efficiency. By addressing speckle noise without requiring well-registered image pairs, this method can enhance image quality and diagnostic accuracy in clinical practice.
Sheath constraints on turbulent magnetised plasmas
Authors: Geraldini A , Brunner S , Parra F I
Published: August 2024

A solid target in contact with a plasma charges (negatively) to reflect the more mobile species (electrons) and thus keep the bulk plasma quasineutral. To shield the bulk plasma from the charged target, there is an oppositely (positively) charged sheath with a sharp electrostatic potential variation on the Debye length scale

λ

D

. In magnetised plasmas where the magnetic field is inclined at an oblique angle α with the target, some of the sheath potential variation occurs also on the ion sound gyroradius length scale

ρ

S

cos
⁡
α

, caused by finite ion gyro-orbit distortion and losses. We consider a collisionless and steady-state magnetised plasma sheath whose thickness

l

ms

∼
max
(

λ

D

,

ρ

S

cos
⁡
α
)

is smaller than the characteristic length scale L of spatial fluctuations in the bulk plasma, such that the limit

l

ms

/

L
→
0

is appropriate. Spatial structures are assumed to be magnetic field-aligned. In the case of small magnetic field angle

α
∼
δ
≡

ρ

S

/

L
≪
1

, electric fields tangential to the target transport ions towards the target via E × B drifts at a rate comparable to the one from parallel streaming. A generalised form of the kinetic Bohm–Chodura criterion at the sheath entrance is derived by requiring that the sheath electric field have a monotonic spatial decay far from the target. The criterion depends on tangential gradients of potential and ion distribution function, with additional nontrivial conditions.
Turbulent relaxation patterns in SOL plasma
Authors: Varennes R , Dif-Pradalier G , Ghendrih P , Grandgirard V , Panico O , Sarazin Y , Serre E , Zarzoso D
Published: August 2024

Relaxations of localized over-density in a plane transverse to the magnetic field are numerically investigated under the effect of drift-wave and interchange drives in SOL conditions. Such a controlled departure from thermodynamic equilibrium allows the investigation of fundamental processes at play in cross-field transport. Interchange instabilities generate ballistic outward radial flux with low amplitude zonal flow patterns, whereas drift-wave instabilities result in symmetric radial flux with large amplitude zonal flow patterns. When both instabilities are considered, the combined effects tend to favor drift-waves, leading to a weaker outward flux with larger zonal flow patterns.
Dislocation proliferation at the growth crystal/seed interface of physical vapor transport-grown 4H-SiC crystals
Authors: Li Huadong , Yang Xianglong , Jiang Xiaocheng , Shao Hongyu , Hu Guojie , Li Xiaomeng , Peng Yan , Chen Xiufang , Hu Xiaobo , Xie Xuejian , Yu Guojian , Xu Xiangang
Published: August 2024

4H-SiC single crystal with [000

1
¯

] direction 4° off axis was prepared by physical vapor transfer method. To enlarge the observed interface area between the seed crystal and the nascent crystal, the wafers were processed at an Angle of approximately 2° in the (000

1
¯

) plane. The longitudinal optical phonon-plasmon coupled (LOPC) mode was measured by a laser Raman spectrometer, and the location of the growth interface was determined by evaluating the free carrier concentration at the seed-crystal interface. The defect structure at the seed-crystal/newly grown crystal interface and in nearby regions was examined by high-resolution x-ray diffractometry. The change in stress at the interface was characterized by a stress tester; the results showed that a greater stress at the interface correlated to more proliferated dislocations. The dislocation morphologies in the interfacial regions of different seed grains etched by molten KOH were observed via microscopy.
Complex dispersion analysis of viscoelastic effects on elastic waves in three-dimensional single-phase metamaterials
Authors: Tang Jincheng , Ma Tian-Xue , Liu Jing , Wang Yue-Sheng
Published: August 2024

In this paper, we study the propagation of elastic waves in three-dimensional single-phase metamaterials using the finite element method. Both elastic and viscoelastic scenarios are considered, where the Kelvin-Voigt model is used to describe the solid material viscosity. We explore the influence of material viscosity on the complex band diagrams and the transmission spectra in detail. It is found that the single-phase metamaterials support both the Bragg scattering and locally resonant band gaps. When a small viscosity is introduced, the wave attenuation within the locally resonant band gaps degrades. However, such a small viscosity has negligible effects on the Bragg scattering band gaps. As the material viscosity increases, the wave attenuation is mainly ascribed to the material viscosity rather than the band gap effects. Additionally, the attenuation behavior of evanescent waves can be accurately predicted from the imaginary part of wave vectors identified in the complex band structures. This work provides a reference for the practical applications of viscoelastic metamaterials.
Stacking integrated learning-based inverse design of four-nanopore high-Q all-dielectric metasurface
Authors: Chen Ying , Wang Qinghui , Han Zhe , Li Weiqiang , Shi Moqing , Zhao Guoting
Published: August 2024

In this paper, we establish a four-nanophole hollowed out all-dielectric metasurface structure as the object of reverse design, which can realize many types of high Q-value Fano resonance effects through dynamic tuning of a single structure, with Q value up to 4401. We used the time domain finite difference method for data collection, and then select appropriate models according to the characteristics of the data from the perspective of the data itself. We select in small sample prediction excellent support vector regression (SVR), gradient promotion decision tree (GBDT), prediction generalization performance and stability of high random forest (RF) as a base learners, with good nonlinear fitting ability BP neural network (BPNN) yuan learners, establish a fusion model based on Stacking integrated learning strategy. Based on this fusion model, the multi-parameter all-dielectric metasurface structure is reverse designed instead. The results show that the proposed method has high prediction accuracy with an absolute average error of only 0.0043, and excellent average accuracy of 82.5%, 77.9% and 14% compared with the combined model GBDT-SVM-BP, GBDT-RF-BP, and RF-SVM-BP. This study provides a new perspective on the reverse design of all-dielectric metasurface structures.
Exceptional points and quantum phase transition in a fermionic extension of the Swanson oscillator
Authors: Sinha Akash , Ghosh Aritra , Bagchi Bijan
Published: August 2024

Motivated by the structure of the Swanson oscillator which is a well-known example of a non-Hermitian quantum system consisting of a general representation of a quadratic Hamiltonian, we propose a fermionic extension of such a scheme which incorporates two fermionic oscillators together with bilinear-coupling terms that do not conserve particle number. We determine the eigenvalues and eigenvectors, and expose the appearance of exceptional points where two of the eigenstates coalesce with the corresponding eigenvectors exhibiting self-orthogonality with respect to the bi-orthogonal inner product. The model admits a quantum phase transition—we discuss the two phases and also demonstrate that the ground-state entanglement entropy exhibits a discontinuous jump indicating the transition between the two phases.
Existence of quantum states for Klein–Gordon particles based on exact and approximate scenarios
Authors: Ortakaya Sami
Published: August 2024

In the present study, Kummer’s eigenvalue spectra from a charged spinless particle located at spherical pseudo-dot of the form r
2 + 1/r
2 is reported. Here, it is shown how confluent hypergeometric functions have principal quantum numbers for considered spatial confinement. To study systematically both constant rest-mass, m
0
c
2 and spatial-varying mass of the radial distribution m
0
c
2 + S(r), the Klein–Gordon equation is solved under exact case and approximate scenario for a constant mass and variable usage, respectively. The findings related to the relativistic eigenvalues of the Klein–Gordon particle moving in the spherical space show the dependence of mass distribution, so it has been obtained that the energy spectra has bigger eigenvalues than m
0
c
2 = 1 fm−1 in exact scenario. Following analysis also shows eigenvalues satisfy the range of E < m
0
c
2 through approximate scenario.
Narrow peaks in excitation spectrum of alkali spin polarization: non-adiabatic case of spin dynamics
Authors: Popov E N , Gaidash A A , Kozubov A V , Voskoboynikov S P
Published: August 2024

We theoretically describe the phenomenon of non-adiabatic spin dynamics, which occurs in a gas cell filled by alkali vapor in the presence of a strong alternating magnetic field and pump light. Steep increase of the spin polarization occurs if the frequency of the magnetic field is equal to the certain value. The observable effect relies on the periodic field that consists of two perpendicular components defined by harmonics with the same amplitudes and different frequencies. The considered effect of the coherent spin motion cannot be explained by a resonance, because the Larmor precession is absent without a constant component of magnetic field. Moreover, there are some clearly visible peaks in the excitation spectrum of spin polarization, which are narrow in comparison to the relaxation rate. Detailed analysis according to proposed quantum model results in the reasoning of the effect via qualitative properties of non-adiabatic dynamics of atomic spin.
Optimization of friction stir processing parameters to improve mechanical properties and microstructure of Al5083 aluminum alloy reinforced with AlCoCrFeNiSi high-entropy alloy
Authors: S Kumaravel , P Suresh
Published: August 2024

This study explores integrating AlCoCrFeNiSi high-entropy alloy (HEA) particles into the Al5083 aluminum alloy matrix via Friction Stir Processing (FSP) to enhance mechanical characteristics. Microstructural analysis reveals a homogeneous distribution and size reduction of HEA particles, contributing to improved structural strength. X-ray diffraction (XRD) examination confirms the formation of solid solution phases in the HEA particles, validating their role in enhancing material properties. Through the utilization of Design of Experiments (DOE) and Response Surface Methodology (RSM), FSP parameters are systematically optimized, enabling precise predictions of mechanical behavior. Multi-response optimization identifies the optimal combination of FSP parameters, resulting in significant enhancements in Ultimate Tensile Strength (UTS) and Hardness, reaching 314 MPa, 42% elongation, and 75 HV, respectively. Scanning Electron Microscopy (SEM) analysis of tensile test specimens elucidates the impact of varied FSP parameters on microstructural features, emphasizing the importance of optimal mixing for improving interfacial bonding and mechanical properties. This study underscores the effectiveness of integrating HEA particles and optimizing FSP parameters to elevate the mechanical properties of Al5083 aluminum alloy, paving the way for tailored composite materials with enhanced performance for specific applications.
Broadband magnetoelectric antenna driven by multiple high-overtone bulk acoustic wave modes
Authors: Wang Qinghui , Xing Yanhui , Hu Rui , Lin Wenkui , Zhang Baoshun , Zeng Zhongming , Han Jun , Huang Zijing , Yun Xiaofan , Xu Dechao
Published: August 2024

High-overtone bulk acoustic waves driven magnetoelectric (ME) antennas operate in the acoustic resonant frequency range, exhibiting continuous narrowband electromagnetic radiation. ME antennas based on cooperative excitation of multiple high-overtone bulk acoustic waves are expected to achieve broadband performance and are worthy of in-depth exploration. High-overtone bulk acoustic resonator (HBAR) antennas with polished and rough acoustic reflection interfaces were fabricated and tested to investigate the influence mechanisms of acoustic modes in the HBAR on the radiation bandwidth, as well as the relationship between antenna impedance and radiation response. Far-field radiation characteristics indicate that the antenna with rough acoustic reflection interfaces featuring more high-overtone bulk acoustic wave modes suppress radiation dips of up to 5 dB at anti-resonant frequencies without sacrificing radiation gain. The radiation gain of the antenna was calculated using the gain-comparison method to be −35 dBi, with a −3 dB bandwidth of 120 MHz and a fractional bandwidth of up to 11.4%. Finally, a comparison of the radiation characteristics of the HBAR piezoelectric antenna without the magnetic film demonstrates that the broadband radiation of the HBAR ME antenna originates from dynamic magnetic flux driven by high-overtone bulk acoustic waves.
Optical, AC conductivity and antibacterial activity enhancement of chitosan-silver nanocomposites for optoelectronic and biomedical applications
Authors: Sarhan A , Fahmy T , Habib A
Published: August 2024

This study is aimed to prepare and investigate the optical, electrical and antibacterial activity of the environmentally friendly (green) chitosan (Cs)/silver nanocomposites. TEM demonstrated that AgNPs have a spherical shape with particle size ranged from 3 nm to 25 nm. UV analysis spectra of Cs and Cs/Ag nanocomposites showed that, increasing the content of AgNPs led to a noticeable increase in the values of Urbach energy (E

U
) and a dramatic decrease in both the indirect (E

ig
) and direct (E

dg
) optical bandgap energies. It is found that (E

ig
) and (E

dg
) are decreased from (4.72/5.31 eV) to (2.47/4.19 eV). The formation of the AgNPs is verified by the existence of surface plasmon resonance (SPR) peak at ∼ (421–450) nm. Wemple-DiDomenico and Sellmeier oscillator models are employed and displayed a clear enrichment in the dispersion energy (E

d
) and oscillator energy (E
0) as well as the linear and nonlinear optical parameters of Cs. It is observed that the linear (χ(1)) and nonlinear (χ(3) and n2) parameters are enhanced from 0.083, 0.868 × 10−14 and 1.584 × 10−12 to 0.153, 9.762 × 10−14 and 4.088 × 10−12. The novel results in our study nominate Cs/Ag nanocomposites for applications in linear/nonlinear optical devices. AC conductivity behavior of Cs and Cs/Ag nanocomposites is analyzed based on Jonscher’s law and the analysis showed that the overlapping large polaron tunneling (OLPT) is the dominant conduction mechanism for our samples. It is clear that the values of dielectric constant (ε′) of Cs and Cs/Ag nanocomposites are higher confirming the presence of interface polarization (IP) relaxation. Moreover, it is found that the antibacterial activity of Cs against Gram-negative (P. aeruginosa) and Gram-positive (B. thuringiensis) bacteria is found to be enhanced with increasing the content of Ag NPs. These results suggested that Cs/Ag nanocomposites will be good source for preparing bio-nanocomposites for use in many biomedical and industrial applications.