bluuebunny/crossref_metadata_2025 huggingface dataset:
Low power tactile sensory neuron using nanoparticle-based strain sensor and memristor
Authors: Bousoulas P. , Mantas S. D. , Tsioustas C. , Tsoukalas D.
Published: November 2024

Endowing strain sensors with neuromorphic computing capabilities could permit the efficient processing of tactile information on the edge. The realization of such functionalities from a simple circuit without software processing holds promise for attaining skin-based perception. Here, leveraging the intrinsic neuronal plasticity of memristive neurons, various firing patterns induced by the applied strain were demonstrated. More specifically, tonic, bursting, transition from tonic to bursting, adaptive, and nociceptive activities were captured. The implementation of these patterns permits the facile translation of the analog pressure signals into digital spikes, attaining accurate perception of various tactile characteristics. The tactile sensory neuron consisting of an RC circuit was composed of a SiO2-based conductive bridge memristor exhibiting leaky integrate-and-fire properties and a Pt nanoparticles (NPs)-based strain sensor with a gauge factor of ∼270. A dense layer of Pt NPs was also used as the bottom electrode for the memristive element, yielding the manifestation of a threshold switching mode with a switching voltage of only ∼350 mV and an exceptional switching ratio of 107. Our work provides valuable insights for developing low power neurons with tactile feedback for prosthetics and robotics applications.
Ultrastrong coupling between molecular vibrations in water and surface lattice resonances
Authors: Verdelli Francesco , Wei Yu-Chen , Scheers Joost M. , Abdelkhalik Mohamed S. , Goudarzi Masoumeh , Gómez Rivas Jaime
Published: November 2024

We investigate the vibrational ultrastrong coupling between molecular vibrations of water molecules and surface lattice resonances (SLRs) sustained by extended arrays of plasmonic microparticles. We design and fabricate an array of gold bowties, which sustain a very high field enhancement, with its SLR resonated with the OH stretching modes of water. We measure a Rabi splitting of 567 cm−1 in the strongly coupled system, whose coupling strength is 8% of the OH vibrational energy, at the onset of the ultrastrong coupling regime (10%). These results introduce metallic microparticle arrays as a platform for the investigation of ultrastrong coupling, which could be used in polaritonic chemistry to modify the dynamics of chemical reactions that require high coupling strengths.
Transition from afterglow to streamer discharge in an atmospheric capacitively coupled micro-plasma jet
Authors: Iseni Sylvain , Nishime Thalita M. C. , Gerling Torsten
Published: November 2024

This Letter focuses on the discharge mechanisms of an atmospheric pressure micro-plasma jet optimized for endoscopic applications in biology and medicine. This capacitively coupled plasma (CCP) features a concentric double flow allowing for shielding the Helium or Neon plasma gas with carbon dioxide from the humid ambient air. High-resolution optical emission spectroscopy allows for the analyses of the Stark effect of the He I 492.19 nm and the Hydrogen Hβ lines to determine the electric field (EF) and the electron density spatially resolved along the discharge expansion outside the source. EF in Neon at atmospheric pressure was reliably determined with the Stark shift measurement of the weak Ne I line at 515.196 nm. In both gases, the EF diagnostic revealed a steep transition from CCP afterglow to streamer discharge with a magnitude up to 30 kV/cm. This research is a significant step forward in the field of plasma medicine with a plasma source capable of delivering a reactive chemistry with or without an intense EF to the target.
Advanced piezoelectric fluid energy harvesters by monolithic fluid–structure–piezoelectric coupling: A full-scale finite element model
Authors: Zhang R. Z. , Cong Y. , Sellam M. , Chpoun A. , Gu S. T.
Published: November 2024

A full-scale finite element model is presented for monolithic fluid–structure interaction (FSI) simulations of thin-walled piezoelectric fluid energy harvesters (PFEHs). Unlike widely used beam/plate-based models, our model employs a solid finite element discretization to precisely represent the complex PFEH designs involving microstructured transducers and non-uniform cantilevers. These features, plus the local FSI effects, are often ignored by simplified models. We applied the Galerkin method to formulate the weak form of the mixed equation system, integrating the flow dynamics, the geometrically nonlinear cantilever, the piezoelectric components, the electrode, and the output circuit within a closed-circuit electro-mechanical coupled system. The coupling of the multiple domains is achieved through boundary-fitted discretization within a monolithic scheme, using shifted-Crank–Nicolson temporal integration. This work explored implementing piezoelectric FSI systems within the FEniCS-based TurtleFSI library, and experimented techniques such as employing penalty functions for achieving electrode components with uniform electric potentials. We investigated various advanced PFEH features, including the baseplate design, the arrangement and microstructure of the piezoelectric components, and their influence on the system's dynamic and energy output behavior. The results confirmed the model's key advantages: full-scale modeling allows the integration of complex base structures and transducer microstructures in PFEH design. Combined with monolithic FSI coupling, it offers greater versatility, supporting a wider range of fluid environments and configurations in both wind and hydropower harvesting. Additionally, the modeling strategy can be intended not only to enhance power output, but also to minimize material usage, reduce mechanical fatigue, and extend the operational lifespan of PFEH systems.
Observation of planar Hall effect in the topological insulator NaCd4As3
Authors: Yang Haiyang , Zhou Yonghui , Wang Jing , Zhou Ying , Han Yuyan , Wang Jialu , Li Yuke , Zhang Xuefeng , Yang Zhaorong
Published: November 2024

The observation of the planar Hall effect (PHE) illuminates the spin textures and topological properties of materials, indicating potential applications in quantum computing and electronic devices. Here, we present a study on the planar Hall transport of topological insulator NaCd4As3 single crystals. When the magnetic field is rotated within the sample plane relative to the current direction, we observe remarkable planar Hall resistivity and giant planar anisotropic magnetoresistance (AMR), both consistent with the theoretical expression of the PHE. Further analysis reveals that the orbital magnetoresistance effect, unrelated to surface electrons from topological surface states or bulk electrons from nontrivial Berry phases, lays a dominant role in the PHE in NaCd4As3. Additionally, the AMR ratio reaches −43% at 3 K under 14 T and remains −9% at room temperature, markedly exceeding that of traditional ferromagnetic metals. These findings provide a platform for understanding the PHE mechanism in topological insulators and highlight the potential of NaCd4As3 for angle and magnetic field detection applications.
High power GaSb-based distributed feedback laser with laterally coupled dielectric gratings at 1.95 µm
Authors: Ding Zhengqing , Cao Juntian , Zhan Kun , Chen Yihang , Zhou Lidan , Wang Weiyuan , Tan Hao , Yang Chengao , Yu Ying , Niu Zhichuan , Yu Siyuan
Published: November 2024

Traditional distributed feedback (DFB) or distributed Bragg reflector (DBR) lasers typically have commonly employed buried gratings as frequency-selective optical feedback mechanisms. However, the fabrication of such gratings often requires regrowth processes, which introduce significant technical challenges, particularly for material systems such as GaAs and GaSb. While metal gratings have been implemented in GaSb-based lasers, they incur additional absorption losses, thereby constraining the device's efficiency and achievable output power. Herein, we introduce a laterally coupled dielectric Bragg grating structure, which enables highly controllable, deterministic, and stable coupling between the grating and the optical mode. Our device demonstrates a continuous-wave output power of 47.02 mW at room temperature, exhibiting stable single-mode operation from 300 to 1000 mA and a maximum side mode suppression ratio of 46.7 dB. These results underscore the innovative lateral coupled dielectric grating as a feasible and technologically superior approach for fabricating DFB and DBR lasers, which hold universal applicability across different material platforms and wavelength bands.
A theoretical study on muoniated N-heterocyclic carbenes using path integral molecular dynamics
Authors: Orikono Satoshi , Kuwahata Kazuaki , Shimazaki Tomomi , Tachikawa Masanori
Published: November 2024

Several N-heterocyclic carbenes (NHCs) are experimentally observed upon the addition of muonium (Mu), and the hyperfine coupling constants (HFCCs) of muon are measured. Theoretical investigation of Mu has been challenging due to significant quantum effects. Herein, we performed an ab initio path integral molecular dynamics (PIMD) simulation, which accurately considers multi-dimensional quantum effects, to theoretically investigate muoniated 1,3-dihydro-2H-imidazole-2-ylidene (Mu-IY). Our findings indicate that quantum effects have two contradictory contributions: the quantum effect of bond vibrations increases the HFCC values, whereas that of out-of-plane angular vibrations decreases the HFCC values. Moreover, we show that the HFCC values of other NHCs can be predicted without the PIMD simulations by applying the structural changes caused by the quantum effect derived from the PIMD simulations of Mu-IY.
Hovering flapping wings with dynamic twist
Authors: Bouard Florian , Jardin Thierry , David Laurent
Published: November 2024

The role of (active) dynamic wing twist on aerodynamic performance of three-dimensional hovering flapping flight is explored using numerical simulations. A variety of cases with different pitch angles and with (flexible wings) or without (rigid wings) dynamic twist are compared. The results show that changes in aerodynamic performance due to dynamic twist are comparable to those obtained without twist (rigid wing cases) by pitching the whole wing and that lift and lift-to-power ratio generally collapse onto a single curve when plotted as a function of the mid-stroke pitch angle at 2/3 wing radius. However, in some cases dynamic twist yields enhanced time-averaged efficiency. Using the force and power partitioning method, it is shown that this enhancement results from the absence of vortical structures near the wing root lower surface and to the presence of an extended leading edge vortex on the wing upper surface, when compared to the most efficient rigid wing case. These differences in flow topology lead to enhanced lift during the early phase of the strokes without changes in power consumption.
Dynamics of an oblate spheroidal particle in a square duct filled with viscoelastic fluids
Authors: Jiang Sen , Ouyang Zhenyu , Lin Jianzhong
Published: November 2024

Herein, we used the fictitious domain method to numerically investigate the lateral migration and rotation of an oblate spheroidal particle in a square duct filled with Oldroyd-B fluids. We adopted Reynolds numbers ranging from 25 to 100 and Weissenberg numbers from 0.01 to 0.50. At low to moderate Weissenberg numbers (Wi ≤ 0.50), viscous forces remain dominant in particle motion. Additionally, we considered the effects of initial lateral position, orientation, and blocking ratio on particle dynamics. The results indicate that for flow in square channels with finite fluid inertia, as Wi increases, the elastic effects gradually strengthen, causing the equilibrium position of the particles to shift from near the centerline of the channel toward the diagonal. Notably, under significant fluid elasticity conditions, additional equilibrium positions emerge in the corners of the channel. When released with their x0–y0 plane (containing the two longest axes of the oblate spheroid) parallel to the x–y plane (duct cross section) of the flow field, particles exhibited three distinct motion modes: tumbling, rolling, and kayaking. Tumbling was influenced by fluid inertia and corner attraction, which exhibited transitions to rolling or kayaking. The study also emphasized that the initial orientation of the particles impacted their sustained tumbling under low inertial flows. In addition, the blockage ratio (the ratio of the equivalent diameter of the particle to the duct height) mainly affected the equilibrium positions, and particles with a blockage ratio β ≤ 0.125 were readily attracted to the corners.
Accurate simulations of moving flexible objects with an improved immersed boundary-lattice Boltzmann method
Authors: Wang Shuangqiang , Yan Haoran , Cai Yunan , Pan Guang , Zhang Guiyong , Song Dong
Published: November 2024

Accurately capturing boundaries is crucial for simulating fluid–structure interaction (FSI) problems involving flexible objects undergoing large deformations. This paper presents a coupling of the immersed boundary-lattice Boltzmann method with a node-based partly smoothed point interpolation method (NPS-PIM) to enhance the accuracy of simulating moving flexible bodies in FSI problems. The proposed method integrates a multiple relaxation time scheme and employs a force correction technique to address boundary capturing inaccuracies. The effect of virtual fluid is accounted for through a Lagrangian point approximation, ensuring precise FSI force calculations for unsteady solid motions. NPS-PIM is utilized as the solid solver, constructing a moderately softened model stiffness by combining the finite element method (FEM) with the node-based smoothed PIM (NS-PIM). Simulations of flow fields near flexible objects with large deformations demonstrate that the proposed approach reduces numerical errors, improves computational efficiency compared to traditional FSI models using FEM and NS-PIM, and accurately captures the behavior of moving flexible bodies and detailed flow fields.
Intrinsic characteristics of three-dimensional flow around a wall-mounted conical cylinder
Authors: Zhu Hongjun , Zhong Jiawen , Zhou Tongming , Alam Md. Mahbub
Published: November 2024

To investigate the flow characteristics around a wall-mounted conical cylinder, three-dimensional direct numerical simulations are carried out for a conical cylinder with an end diameter ratio ranging from 0.5 to 1.5 at three low Reynolds numbers (Re = 100, 150, 200). The flow features are examined in terms of time-mean streamlines, singularity points location, topological structure, time-mean streamwise vortices, and instantaneous spanwise vortices denoted with different vortex identification methods. The downwash effect also happens even without a free end. The upwash streamlines clash with the downwash streamlines and then coalesce to the saddle (impingement) point P2. The occurrence of the symmetry plane belongs to a new topology, where the saddle point on the bottom wall is an attachment point (NA), instead of the separation point (SS). The singular point verifies the topological existence of the attachment–attachment combination of the horseshoe vortex system. The “Quadrupole Type,” “Sextupole Type,” and “Octupole Type” are identified. The “Octupole Type” is reported first, consisting of a pair of “time-mean streamwise tip vortices,” two pairs of “time-mean streamwise base vortices” and a pair of “time-mean streamwise bottom vortices.” Moreover, the vorticity magnitude cannot represent the occurrence of vortices. The instantaneous iso-surfaces of Q = 0.2 and λ2 = –0.2 in the wake are similar to the threshold of Ω = 0.52. In contrast, the Liutex/Rortex method is easier to identify the streamwise bottom vortices than the former two methods.
A simulation study on the influence of marginal pinching upon liquid film dynamics
Authors: Lian Tongda , Matsushita Shintaro , Aoki Takayuki
Published: November 2024

In fluid dynamics, the generation and bursting of surface bubble liquid films in surfactant-laden environments involve complex phenomena, one of which is marginal pinching at the film's foot—a crucial yet inadequately understood aspect due to experimental limitations. Considering its profound impact on liquid film drainage and lifetime, we utilize high-resolution numerical simulations incorporating a weakly compressible scheme and adaptive mesh refinement to dissect the marginal pinching dynamics with unprecedented detail. Our approach elucidates the pinching dynamics and tracks the evolution of film thickness during the critical late-stage drainage process. By leveraging detailed geometric data from pinched regions, we significantly refine existing drainage models, enhancing their predictive accuracy regarding rupture thickness and film lifetime across various viscosities, surfactant concentrations, and bubble sizes. This refined model demonstrates robust alignment with our simulation results. Furthermore, we establish a quantifiable relationship between the prefactor governing reverse flow induced by the Marangoni effect and surfactant concentration. The methodologies and findings of this study provide foundational knowledge that paves the way for optimized industrial processes and an enhanced understanding of natural phenomena.
Mechanism of airfoil stall flutter: New insights from global linear stability analysis
Authors: Li Xintao , Cui Yonghe , Li Baoliang , Ge Mingwei
Published: November 2024

Stall flutter is a self-excited aeroelastic vibration phenomenon that occurs in lifting systems near the stall angle of attack, characterized by the distinct single-degree-of-freedom behavior. Despite its significance, this phenomenon remains not fully understood and is often vaguely attributed to nonlinear effects. To address this gap, the present study aims to reveal the underlying fluid–structure interaction mechanisms of stall flutter through global linear stability analysis (LSA). For this purpose, a reduced-order model (ROM)-based aeroelastic stability analysis framework is established using the autoregressive with exogenous input method. The ROM-based aeroelastic model provides a low-order representation of the coupled dynamics near the equilibrium steady state and can accurately capture the stability characteristics of the fluid-elastic system. It is found that as the angle of attack approaches the static stall angle, a low-frequency weakly stable fluid mode emerges, whose frequency is sufficiently lower than that of the von Kármán vortex shedding. The interaction between this fluid mode and the structure mode ultimately leads to the instability of the aeroelastic system at high reduced velocities, which is the fundamental cause of stall flutter. Moreover, dynamic mode decomposition is employed to successfully extract the spatial coherent structures and frequency characteristics of this low-frequency fluid mode, thereby confirming the validity of the LSA results. Further analysis indicates that, as the angle of attack decreases, this low-frequency fluid mode gradually weakens and eventually degenerates into more stable non-oscillatory fluid modes, resulting in structural stabilization and the cessation of stall flutter. Overall, the linear dynamic model accurately predicts the onset of instability and the vibration frequency of the airfoil, which challenges the traditional nonlinear perspectives and supports the feasibility of using linear control theory for stall flutter suppression in future research.
Broadband cavity-enhanced optical flux monitoring
Authors: Rousseau Roman , Botella Claude , Morville Jérôme , Bounab Mohamed , Berguiga Lotfi , Furgeaud Clarisse , Bachelet Romain , Saint-Girons Guillaume
Published: November 2024

This work describes a new type of sensor for growth process monitoring named broadband cavity-enhanced optical flux monitoring sensor (BBCE-OFM). Like existing optical flux monitoring (OFM) solutions, it relies on absorption spectroscopy. However, the implementation of an optical cavity reduces the measurement uncertainty, enabling efficient operation even at very low growth rates. Using the BBCE-OFM sensor mounted in our solid-source oxide molecular beam epitaxy reactor, we achieved an uncertainty of ±2% on the measurement of Sr and Ti growth rates in SrTiO3 at around 1 Ml/min, to be compared to the ±16% obtained in the same conditions using a conventional OFM setup. Furthermore, our sensor architecture, based on an echelle monochromator and LEDs replacing the hollow cathode lamps used in standard OFM sensors, is more robust against drift.
Coherent flow structures and magnetic field patterns in rotating spherical shell convective dynamos: A data-driven approach
Authors: Mukherjee Priyabrata , Sahoo Swarandeep
Published: November 2024

The Earth's outer core dynamics involve convective fluid motion generating an observable geomagnetic field. The velocity and magnetic fields exhibit characteristic spatiotemporal features possessing geophysical significance for which extensive datasets are available from direct observations and computational simulations. This study demonstrates the robustness of proper orthogonal decomposition (POD), a data-driven technique, in detecting prominent and relevant features in these datasets. Improvising on previous practices, the POD efficiently detects infinitesimal instabilities at the onset of convection, providing an accurate and objective methodology to determine the convective threshold, even for heterogeneous buoyancy forcing. Time evolution of paired, phase-shifted modes efficiently reconstructs the azimuthally drifting of traveling wave instabilities. Simultaneously reduced order modeling of velocity components clearly distinguish the equatorial and polar coherent flow structures. Supercritical convection-driven magnetic field data over long periods, generated using numerical simulations, produce dominant modes that are more accurately representative of time-averaged patterns than geocentric axial dipole patterns. Moreover, the quantitative significance of the dominant modes determines the extent of dimensional reduction complementing established diagnostics for dipolarity. Finally, analysis of observational geomagnetic field data reveals long-lived dominant patterns influenced by thermal core–mantle interaction consistent with numerical models employing tomographic heat flux boundary conditions in present as well as previous studies.
Assessing many-body methods on the potential energy surface of the (H2)2 hydrogen dimer
Authors: Contant Damian , Casula Michele , Hellgren Maria
Published: November 2024

The anisotropic potential energy surface of the (H2)2 dimer represents a challenging problem for many-body methods. Here, we determine the potential energy curves of five different dimer configurations (T, Z, X, H, and L) using the lattice regularized diffusion Monte Carlo method and a number of approximate functionals within density functional theory (DFT), including advanced orbital-dependent functionals based on the random phase approximation (RPA). We assess their performance in describing the potential wells, bond distances, and relative energies. The repulsive potential wall is studied by looking at the relative stability of the different dimer configurations as a function of an applied force acting along the intermolecular axis. It is shown that most functionals within DFT break down at finite compression, even those that give an accurate description around the potential well minima. Only by including exchange within RPA, a qualitatively correct description along the entire potential energy curve is obtained. Finally, we discuss these results in the context of solid molecular hydrogen at finite pressures.
First-principles study on a new 2D carbon allotrope with an intrinsic wide bandgap: A comparison with α-graphyne
Authors: Li Wentao
Published: November 2024

Nanocarbon materials with intrinsic electronic bandgaps are highly desirable for next-generation carbon-based nanoelectronics. Herein, a new two-dimensional (2D) carbon allotrope with structural similarities to α-graphyne has been proposed theoretically, which exhibits intrinsic semiconducting behavior with a wide direct bandgap significantly larger than that reported in other 2D carbon allotropes. Based on first-principles calculations, the structural and electronic properties of the new 2D carbon allotrope, as well as its lattice stability, have been systematically investigated by adopting a comparative study with α-graphyne. Moreover, the effects of vertical stacking and in-plane biaxial strain on the new 2D carbon allotrope have also been clarified in this work, providing robust approaches for the effective modulation of electronic properties in the new 2D carbon allotrope. Thus, the intrinsic wide bandgap, along with effective modulations, suggests great advantages and potentials of the new 2D carbon allotrope in carbon-based electronic devices and light-emitting applications.
Slow global motions in biosolids studied by the deuteron stimulated echo NMR experiment
Authors: Krushelnitsky Alexey , Shahsavan Farhad , Hempel Günter , Fatkullin Nail
Published: November 2024

Recent 15N R1ρ-relaxation studies have shown that proteins in the solid state undergo slow, low amplitude global motion in the sub-millisecond time range. This range is at the edge of the time window for R1ρ experiments and, therefore, the motional parameters obtained by this method are not precise or reliable. In this paper, we present a 2H stimulated echo study of this type of molecular dynamics. The 2H stimulated echo experiments on a static sample allow for direct measurement of the correlation function in the time range of 10−6–10−1 s, making them well suited to study this type of molecular mobility. We have conducted a detailed analytical and numerical comparison of the correlation functions obtained from the relaxation and stimulated echo experiments, which are generally different. We have identified conditions and algorithms that enable a direct comparison of the relaxation and stimulated echo experimental results. Using the protein GB1 in the form of a lyophilized powder, we have demonstrated that 15N R1ρ-relaxation and 2H stimulated echo experiments yield essentially the same slow-motion correlation function. Surprisingly, this type of motion is observed not only in the protein sample but also in the tripeptide and single amino acid solid samples. The comparison of data measured in these three samples at different temperatures led us to conclude that this slow motion is, in fact, ultrasonic phonons, which seem to be inherent to all rigid biological solids.
Programmable orientation of blue phase soft photonic crystal
Authors: Zhang Yuxian , Zheng Zhi-Gang
Published: November 2024

Understanding the structure formation and its underlying physical mechanism is a fundamental topic in condensed matter systems, with both academic and practical implications. Soft matter is playing a remarkable role in current era of information explosion, demonstrating enormous potential in integrated functional photonics. As unique soft photonic crystals with cubic symmetries, not only liquid crystalline blue phases (BPs) have circularly polarized selective reflection and ultra-fast electro-optical response, but also their three-dimensional photonic structures increase degrees-of-freedom for multiplexed optical modulation. In the thriving field of soft-matter-based photonics, precise and programmable engineering of BP crystal orientation is of vital importance for planar optical elements, which remains a challenging task due to the complexity of the nucleation process as well as the interaction between the BP building blocks and the boundary conditions. Aiming to gain a comprehensive understanding of how to tailor the orientation of BP crystals for the photonic applications of next generation, here we discuss the solutions for uniformity improvement and orientation control of BP crystals, about which a few of examples in combination with the underlying mechanisms are explained. In addition, the remaining challenges and the efforts that are expected are also reviewed. We expect this work provides a deeper understanding of phase transitions and resulting structures in soft crystals, which may open encouraging perspectives for their applications in photonics, biosensing, interfacial, and chemical engineering.
Influence of temperature and crack-tip speed on crack propagation in elastic solids
Authors: Persson B. N. J.
Published: November 2024

I study the influence of temperature and the crack-tip velocity of bond breaking at the crack tip in rubber-like materials. Bond breaking is considered as a stress-aided thermally activated process and results in an effective crack propagation energy, which increases strongly with decreasing temperature or increasing crack-tip speed. This effect is particularly important for adhesive (interfacial) crack propagation but less important for cohesive (bulk) crack propagation owing to the much larger bond-breaking energies in the latter case. For adhesive cracks, the theory results are consistent with adhesion measurements for silicone rubber polydimethylsiloxane (PDMS) in contact with silica glass surfaces. For cohesive cracks, the theory agrees well with experimental results PDMS films chemically bound to silanized glass.
The durability of viscosity reduction of magnetically treated waxy crude oil
Authors: Su Yang , Li Hongying , Li Quande , Xie Yiwei , Liang Bing , Zhang Chaoyue , Kang Jiabao , Yang Zhaoming , Su Huai , Zhang Jinjun
Published: November 2024

Magnetic treatment is a method for improving the cold flowability of waxy oils. Previous studies have predominantly focused on the viscosity reduction resulted from the treatment, with the durability of the magnetic effect neglected, which is crucial for pipeline transportation of the treated crude oil. Therefore, this study focuses on the durability and its mechanism of the magnetic effect of a waxy crude oil under static, low shear, and high shear conditions. A viscosity reduction of 15.7% was achieved under the magnetic treatment condition of the magnetic treatment temperature at 52 °C, magnetic field strength at 0.1 T, and a duration of 1 min. However, the magnetic effect gradually diminished with time elapsing and disappeared in 9 h under static conditions. Shear was found to be beneficial to the preservation of the effect, and a correlation between the viscosity of the sheared treated-oil and the energy dissipation of the shear was found. Microscopic observations, impedance measurements, and x-ray diffraction analysis revealed that exposure to a magnetic field might disperse the charged particles, i.e., resins and asphaltenes, in the crude oil, facilitating their adsorption on the wax particle surfaces, thus enhancing electrostatic repulsion among wax particles and resulting in viscosity reduction. The desorption of the adsorbed resins and asphaltenes from the wax particles and reaggregation lead to the gradual diminishment of the viscosity reduction. Shear might inhibit this reaggregation and thus contribute to the durability of the viscosity reduction.
An experimental investigation of boundary layer over permeable interfaces in Hele-Shaw micromodels
Authors: Del Mastro Mario , Terzis Alexandros
Published: November 2024

This study experimentally investigates boundary layer development over permeable interfaces using Hele-Shaw micromodels and high-resolution micro-particle image velocimetry (micro-PIV). Velocity vectors, captured at a 5 μm scale, reveal the flow behavior at the interface between free-flow and porous media with ordered structures and porosities ranging from 50% to 85%. The results show that the boundary layer streamline alignment decreases with increasing porosity, while lower permeability fosters more uniform and parallel flow near the interface. Flow channeling occurs along paths of the least resistance, with more flow directed through the Hele-Shaw free-flow region as the solid fraction of the porous material increases. The Reynolds number (0.14–0.94), based on the Hele-Shaw hydraulic diameter, has a minimal effect on the normalized velocity distribution. Furthermore, an analytical solution for the external boundary layer thickness exhibited good agreement with experimental data, confirming a thickness of 2–4 times the square root of the free-flow Hele-Shaw permeability. Additionally, a Q-criterion analysis identified, for the first time, distinct zones within the external boundary layer, capturing the balance between rotational and deformation components as a function of permeability. These findings offer insight into flow dynamics in porous media systems, with implications for both natural and industrial applications, and contribute to the improved modeling of fluid dynamics and momentum transport in coupled free-flow and porous media environments.
Manipulating crack formation in air-dried clay suspensions with tunable elasticity
Authors: Parmar Vaibhav Raj Singh , Bandyopadhyay Ranjini
Published: November 2024

Clay, the major ingredient of natural soils, is used as a rheological modifier while formulating paints and coatings. When subjected to desiccation, colloidal clay suspensions and clayey soils crack due to the accumulation of drying-induced stresses. Even when desiccation is suppressed, aqueous clay suspensions exhibit physical aging, with their elastic and viscous moduli increasing over time as the clay particles self-assemble into gel-like networks due to time-dependent inter-particle screened electrostatic interactions. The rate of evolution of the suspension structures and therefore of the mechanical moduli can be controlled by changing clay concentration or by incorporating additives. Since physical aging and desiccation should both contribute to the consolidation of drying clay suspensions, we manipulate the desiccation process via alterations of clay and additive concentrations. For a desiccating sample with an accelerated rate of aging, we observe faster consolidation into a semi-solid state and earlier onset of cracks. We estimate the crack onset time, tc, in direct visualization experiments and the elasticity of the drying sample layer, E, using microindentation in an atomic force microscope. We demonstrate that tc∝GcE, where Gc, the fracture energy, is estimated by fitting our experimental data to a linear poroelastic model that incorporates the Griffith's criterion for crack formation. Our work demonstrates that early crack onset is associated with lower sample ductility. The correlation between crack onset in a sample and its mechanical properties as uncovered here is potentially useful in preparing crack-resistant coatings and diverse clay structures.
Insight into the impact of fixed transition on the aerodynamic performance and noise of airfoils with varying airfoil thicknesses
Authors: Lv Changrui , Ye Xuemin , Wu Yingming , Li Chunxi
Published: November 2024

To explore the effect of surface pollution on the aerodynamics and acoustics of airfoils, the aerodynamic performance and noise of Delft University of Technology (DU) airfoils with different relative thicknesses are simulated using the shear-stress transport k-ω model and large Eddy simulation. The sensitive positions of fixed transition for DU airfoils are examined in terms of aerodynamic performance and noise, and the variations in aerodynamic performance, noise, and internal flow are analyzed. The results show that the sensitive position of fixed transition is almost unaffected by the relative thickness of airfoils. In terms of aerodynamic performance and noise, the sensitive transition positions on the suction surface are located at 1%c and 5%c, respectively. Fixed transition leads to a reduction in the aerodynamic efficiency and an elevation in noise. The impact of fixed transition on the airfoil's trailing-edge noise far exceeds its effect on radiated noise. The original airfoil's noise exhibits a typical dipole-like directional distribution. However, after the fixed transition, the dipole distribution gradually blurs, and this trend becomes more pronounced with increasing relative thickness. Fixed transition reduces the stability of wake vortex shedding and increases the energy loss, and an increase in relative thickness enlarges the high vortex region and vortex size near the fixed transition.
Orientation-dependent strain and dislocation in HVPE-grown
α
-Ga2O3 epilayers on sapphire substrates
Authors: Zhang Yijun , Shen Yang , Cui Mei , Liu Jing , Xie Dabao , Ren Fangfang , Gu Shulin , Zheng Youdou , Zhang Rong , Ye Jiandong
Published: November 2024

Orientation-dependent substrates provide effective platforms for achieving α-Ga2O3 with low dislocation densities, whereas the associated strain and dislocation dynamics have not been fully explored. Herein, we investigated the evolution of growth mode, interfacial strain, and dislocation propagation in the α-Ga2O3 epitaxial layer with various orientations, grown by the halide vapor-phase epitaxy. Strain tensor theory and geometric phase analysis indicate that the m-plane α-Ga2O3 epitaxial layer exhibits the lowest misfit tensile strain, measured at εxx = 1.46% and εyy = 1.81%, resulting in the lowest edge dislocation density. The m-plane lattice exhibits an inclination of 33.60°, while the c-plane lattice is horizontally aligned and the a-plane lattice oriented perpendicularly. The orientation-dependent growth significantly influences stress relaxation through the generation of misfit dislocations, originating from either basal or prismatic slip. Edge dislocations, induced by misfit dislocations, favor the c-axis, remaining well confined within the in-plane interfacial layer of the m-plane α-Ga2O3, leading to reduced low edge dislocation density in the subsequent thick epitaxial layer. These findings shed light on the epitaxial dynamics of α-Ga2O3 heteroepitaxy, paving the way for the development of high-performance power devices.
Spatiotemporal structure of flow field by a dielectric-barrier-discharge plasma actuator using phase-resolved particle image velocimetry
Authors: Mishra Bal Krishan , Panigrahi P. K.
Published: November 2024

A typical dielectric-barrier-discharge plasma actuator (DBD-PA) operating in continuous mode generates a self-similar starting vortex followed by a quasi-steady wall jet. In the burst mode, it generates periodic vortices, leading to a spatially wider mean flow field. The characteristics of periodic vortices can be controlled by adjusting the duty cycle α and burst frequency fb of the actuation signal. In the present study, the flow field generated by the actuator in burst mode is studied for 50%≥α≤90%, and 10 Hz ≥fb≤90 Hz. The Reynolds number of mean flow based on the maximum induced velocity and jet half-width ranges from 171 to 524. High-speed laser-sheet visualization and time-resolved particle image velocimetry are used for flow field measurements. The flow field generated during burst mode operation shows the strong influence of the burst frequency. Periodic vortices with comparable size and convection speed of starting vortex are generated at low fb. Dipoles and small-scale vortices are formed at moderate fb similar to the behavior of a transitional wall jet. Kelvin–Helmholtz instability is observed at higher burst frequency. An ornamental vortex consisting of several small periodic vortices is formed at high values of fb during the starting period. Based on the temporal evolution of momentum, the flow field generated by the DBD-PA can be classified into (i) starting flow regime, (ii) transitional flow regime, and (iii) periodic flow regime. The self-similarity of the mean flow field generated by the DBD-PA is verified by comparing the mean velocity profile at multiple downstream locations with the self-similar solutions of laminar and turbulent wall jets. The entrainment coefficient of the mean flow field is similar to that of an axisymmetric turbulent wall jet. The bi-orthogonal analysis shows that both coherent mode energy content and the entropy are minimum (about 5% only) for the continuous mode actuation. For the burst mode actuation, both the coherent mode energy content and the entropy are higher in magnitude compared to that of continuous mode and decrease with increasing burst frequency. The vortices in the periodic flow regime are locked in with fb. The distance between subsequent vortices, λx and flow frequency, f follow a power-law relationship, λx=cf−n, where c is a constant and n can be approximated as 2/3.
Effect of gap width on flow structure and reattaching characteristic of two tandem 5:1 rectangular cylinders: Experimental and numerical studies
Authors: Wang Peiyuan , Li Jingyang , Zhao Yongfei , Wang Shaowei , Li Shaopeng
Published: November 2024

The flow structure and reattaching characteristic of two tandem rectangular cylinders with aspect ratio being 5:1 have been investigated through wind tunnel experiments and three-dimensional large eddy simulation (LES) methods. The gap width G between the two cylinders varies from 2 times of D to 20 times of D, where D represents the depth of the two cylinders. The surface pressure distribution and aerodynamic forces of each cylinder are obtained via wind tunnel experiments. Two distinct flow patterns are identified with the increasing G through three-dimensional LES methods, and the aerodynamic results are presented in good agreement with the experiments as well. The experimental and numerical results indicate that the flow structure is highly sensitive to the variation in G, leading to alterations in the aerodynamics and vortex-shedding characteristic of two cylinders. Furthermore, the simulation results also capture the shift in the reattaching points as G increases. Additionally, following the simulation findings, a proposed criterion based on the wind tunnel experimental data is presented for predicting the boundary layer reattachment points on two tandem 5:1 rectangular cylinders.
Micromechanical properties and fractal homogenization of coal based on nanoindentation
Authors: Zhu Yongjian , Lin Qiangwei , Luo Yafei , Li Wenbin , Huang Fei , Zhang Zizheng , Wu Qiuhong
Published: November 2024

Distinct from hard rock, coal is relatively soft and fragmented. It is not only challenging to prepare test coal samples that meet the requirements of standard mechanical experiments but also impossible to recycle them for repeated testing. There is an urgent need to explore new mechanical testing methods to enhance the study of the mechanical properties of coal. In this study, the micromechanical parameters of the coal matrix solid phase were acquired through targeted nanoindentation technology. The elemental composition, surface morphology, and pore structure characteristics of each indentation point were determined by energy dispersive spectrometer, optical microscope observation, and high-pressure mercury injection experiments. The fractal homogenization equation is deduced based on fractal geometry and the Mori–Tanaka method. The validity of the fractal homogenization approach is verified by integrating the micromechanical parameters and pore structure characteristics of coal, and the impact of the microstructural parameters on the macroscopic mechanical properties of coal is discussed. The results show that the proportion of clay minerals in the solid phase of the coal is the greatest (81.18%), with the main mineral components being kaolinite and illite. The elastic modulus is 1.974 ± 1.036 GPa, the hardness is 0.131 ± 0.108 GPa, and the ratio of upper and lower pore scales conforms to the fractal calibration rate. The macroscopic equivalent elastic modulus rises along with the increase in the fractal dimension. When the fractal dimension is constant, the macroscopic equivalent elastic modulus decreases with the increase in λmin/λmax and increases with the increase in solid phase elastic modulus.
Visualization experiments and numerical simulation on the growth of fracture height in bedding-rich reservoirs
Authors: Huang Guopeng , Li Minghui , Zhou Fujian , Chu Jinqi , Xiong Zhuang
Published: November 2024

The development of shale bedding and differences in properties have significant effects on the growth of the fracture height. To investigate the impact mechanism of bedding on the fracture growth height, the visualization fracturing experiments based on polymethylmethacrylate (PMMA) samples were performed to investigate the impact of the injection rates, viscosity and temporary plugging parameters on the growth pattern of hydraulic fractures. Furthermore, the solid–fluid-damage fracturing coupled model considering the vertical distribution of bedding was constructed by the continuous-discontinuous element method, and the impact of key formation parameters and treatment parameters were investigated. The results show that the height growth pattern of PMMA samples was affected by the flow rate and fluid viscosity. The fracture can cross the bedding at high-viscosity fluid. But in low-viscosity fluid the fracture tends to be arrested by the bedding. And the fracture cannot cross the bedding again after In-fracture temporary plugging. The fractures vertical growth pattern mainly includes three types at various stratigraphic parameters and treatment parameters, “工” type fracture, “丰” type fracture, and “I” type fracture, respectively. For vertical stress differentials below 3 MPa or Young's modulus below 20 GPa or injection rates below 1.8 m3/min or the fluid viscosity below 5 mPa·s, the fracture will be limited within the bedding.
Overexpression of HvVDE gene improved light protection in transgenic tobacco (Nicotiana tabacum)
Authors: Qu Xiaojie , Che Deyu , Qin Fangting , Huang Guang , Liu Hongzhang
Published: November 2024

Hosta is commonly acknowledged as a popular and preferred plant for landscaping and gardening. The ‘sunburn’ caused by prolonged exposure to strong sunlight is reducing the ornamental values of Hosta plants. However, there is a scarcity of research focusing on the genetic components linked to light-induced harm in Hosta. Here, the violaxanthin de-epoxidase (VDE) homolog from Hosta ventricosa was isolated and functionally identified through conducting HvVDE-overexpression tobacco (Nicotiana tabacum) lines. The results showed that HvVDE encodes a putative protein comprising 481 amino acids with a molecular weight of 54.304 kDa. The phylogenetic analysis found that HvVDE exhibited close similarity to JcVDE. Besides, the expression patterns of HvVDE found that HvVDE was expressed differently across tissues, withexpression induced by high light intensities. And overexpression of HvVDE led to the restoration of non-photochemical quenching in tobacco, suggesting that HvVDE plays a role in dissipating excess light energy as thermal energy in H. ventricosa. These findings underscore the significance of HvVDE in mitigating photoinhibition and enhancing photoprotection mechanisms in H. ventricosa.