bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ship Radiated Noise Signal Denoising Method With SVMD-AAPE-RPE-CC-AWTD
Authors: Lu Binjie , Zhang Xiaobing , DAI Zhonghua , Yuan Peilong 
Published: August 2024

Abstract
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

Abstract
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

Abstract

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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.
A robust color image encryption scheme with complex whirl wind spiral chaotic system and quadrant-wise pixel permutation
Authors: Ponnambalam Maran , Ponnambalam Mathivanan , Jamal Sajjad Shaukat 
Published: August 2024

Abstract
This paper presents a novel encryption technique that uses a unique chaotic circuit design called as 3D Complex Whirl Wind Spiral chaotic system (CWWS). The major goal of this novel approach is to create an efficient 3D chaotic systems with increased randomness and multistability, specifically designed to encrypt multimedia data. The design incorporates the sine function sin(x) to introduce complexity and unpredictability in the chaotic circuit. The dynamic behaviour of the proposed scheme’s chaotic system is thoroughly evaluated using a variety of analyses, including KY dimension, dissipativity, Lyapunov exponent spectra, and bifurcation diagrams. There are two key stages to the encryption process: diffusion and confusion. The diffusion process is strengthened by the smooth integration of quadrant-wise pixel permutation (QWPP) algorithms, which eliminate correlations between neighbouring pixels. Following that, the image components are concealed using the chaotic sequence that was generated from the 3D CWWS chaotic system. The complete encrypted image is then created by combining these encrypted components. The simulation results of the proposed strategy are thoroughly investigated using statistical analysis, differential analysis, and brute force attacks. The system has optimal key space, entropy, UACI, and NPCR metric values of 2400, 7.99, 0.334, and 0.996, respectively. Furthermore, the experimental findings show robust resistance to statistical, differential, and brute force attacks for a single round of iteration.
A Study of the Comets with Large Perihelion Distances C/2019 L3 (ATLAS) and C/2019 O3 (Palomar)
Authors: Betzler Alberto S. 
Published: August 2024

Abstract
This work analyzes the photometric data of the Oort spike comets C/2019 L3 (ATLAS) and C/2019 O3 (Palomar) obtained between 2016 and 2023 by the ATLAS network and the Belgian Olmen Observatory. The comets Palomar and ATLAS have a typical and unusually high activity level, respectively, based on the Afρ parameter corrected to phase angle zero at perihelion. The absolute magnitude of comets ATLAS and Palomar in the o-band is 4.71 ± 0.05 and 4.16 ± 0.02 respectively. The cometary activity of comets ATLAS and Palomar probably began at r > 13 au before perihelion and will end at r >14 au after perihelion, which means that they could remain active until the second half of 2026. The nucleus of comet ATLAS has a minimum radius of 7.9 km, and the nucleus of comet Palomar could be a little larger. The c − o colors of the comets ATLAS and Palomar are redder and bluer, respectively, at perihelion than the solar twin YBP 1194. These comets showed a bluish trend in the coma color with decreasing heliocentric distance. Comet Palomar probably had two outbursts after its perihelion, each releasing about 108 kg of dust. The slopes of the photometric profile of the comae of these comets were between 1 and 1.5, indicating a steady state during the observation campaign.