bluuebunny/crossref_metadata_2025 huggingface dataset:
Amplitude and time response characterization of avalanche signals in InGaAs single-photon avalanche diode
Authors: Shi Ming , Zhang Weimin , Zhou Bingyu , Hou Jin , Yang Chunyong , Wang Rui
Published: October 2024

Photon and dark avalanche signals of InGaAs single-photon avalanche diodes (SPAD) are detected and counted indiscriminately, while their specific characteristics are not well understood, which hinders further performance optimization of InGaAs SPAD. Here, we investigate back-incidence InGaAs SPAD operating at room temperature by designing a dual-threshold discriminator and tuning the threshold voltage. The photon count rate and dark count rates (DCR) exhibit different abrupt-voltage variations with the threshold voltage, and the amplitude distribution of dark avalanche signals is more concentrated and slightly larger than that of photon avalanche signals. The smaller photon avalanche signals have a faster time response. It can be inferred that the above characteristics are related to the photon absorption position and carrier transport, depending on physical structure and operating mode, and dark counts are mainly caused by holes drifting from N-type material. We use a dual-threshold discriminator to reduce the time jitter and DCR caused by thermally excited carriers. The experimental results are in good agreement with theoretical analysis, indicating that the insertion of an i-InP layer or the use of a front-incidence technique can further optimize the overall performance and enable InGaAs SPAD with high performance operation at room temperature.
Shrimp-shaped structure and period-bubbling route to chaos in a one-dimensional economic model
Authors: Kumbhakar Ruma , Karmakar Sarbari , Pal Nikhil , Kurths Jürgen
Published: October 2024

A beautiful feature of nature is its complexity. The chaos theory has proved useful in a variety of fields, including physics, chemistry, biology, and economics. In the present article, we explore the complex dynamics of a rather simple one-dimensional economic model in a parameter plane. We find several organized zones of “chaos and non-chaos” and different routes to chaos in this model. The study reveals that even this one-dimensional model can generate intriguing shrimp-shaped structures immersed within the chaotic regime of the parameter plane. We also observe shrimp-induced period-bubbling phenomenon, three times self-similarity of shrimp-shaped structures, and a variety of bistable behaviors. The emergence of shrimp-shaped structures in chaotic regimes can enable us to achieve favorable economic scenarios (periodic) from unfavorable ones (chaotic) by adjusting either one or both of the control parameters over broad regions of these structures. Moreover, our results suggest that depending on the parameters and initial conditions, a company may go bankrupt, or its capital may rise or fall in a regular or irregular manner.
Characterizing firebrands and their kinematics during lofting
Authors: Petersen Alec J. , Banerjee Tirtha
Published: October 2024

Spot fires pose a major risk and add to the already complex physics, which makes fire spread so hard to predict, especially in the wildland urban interface. Firebrands can not only cross fuel breaks and thwart other suppression efforts but also directly damage infrastructure and block evacuation routes. Transport models and computational fluid dynamics tools often make simplifications when predicting spot fire risk, but there is a relative lack of experimental data to validate such parameterizations. To this end, we present a field experiment performed at the University of California Berkeley Blodgett Research Forest in California where we recorded the flame and firebrands emanating from a nighttime hand-drawn pile fire using high-frequency imaging. We used image-processing to characterize the fire intensity and turbulence as well as particle tracking velocimetry to measure ejected firebrand kinematics as they are lofted by the plume. We further collected embers that settled around the fire at varying distances and measured their size, shape, density, and settling distributions. We also examine existing physics-based time-averaged models of firebrand lofting and note discrepancies between such models, often used due to their speed and simplicity, and our experimental observations. Finally, we discuss some implications our observations could have on future modeling efforts by considering the time-dependent fire dynamics, intermittency in the plume turbulence, and in the firebrand generation rate. To the best of our knowledge, these are the first in situ observations of firebrand generation and lofting from representative fuels, addressing a major source of data gap and uncertainty in the wildland fire literature.
Unsteady solute dispersion in large arteries under periodic body acceleration
Authors: Das Santanu , Mahata Kartick , Patne Ramkarn , Kumar Sanjeev , Rana Jyotirmoy
Published: October 2024

The present study investigates the effect of periodic body acceleration on solute dispersion in blood flow through large arteries. Transport coefficients (i.e., exchange, convection, and dispersion coefficients) and mean concentration of the solute are analyzed in the presence of wall absorption. The solute is quickly transported to the wall of arteries with a smaller radius, whereas the opposite is true for arteries with a larger radius. In the presence of body acceleration, the amplitude of fluctuations of the convection coefficient K1(t) increases significantly as the radius of the artery increases. In contrast, an opposite scenario exists for the dispersion coefficient K2(t). The solute dispersion process becomes more effective in arterial blood flow as the radius of the artery decreases. More interestingly, in large arteries with body acceleration, the solute is convected, dispersed, and distributed more toward the upstream direction owing to flow reversal during the diastolic phase of pressure pulsation. Note that this important feature of flow reversal is solely due to periodic body acceleration. For an artery with a small radius, under the influence of periodic body acceleration, the mean concentration of solute Cm is the minimum, and more axial spread is noticed in the axial direction. In contrast, an opposite scenario arises in the artery with a large radius. Additionally, the effect of body acceleration on the shear-induced diffusion of red blood cells is discussed in blood flow.
Modulating local winds and turbulence around a single building obstacle with the obstruction of tall vegetation
Authors: Duan G. , Bi Z. , Zhao L. , Yang T. , Takemi T.
Published: October 2024

Strategic vegetation placement can significantly alter airflow patterns and turbulence, fostering desired wind environments. By comparing scenarios where vegetation is placed upstream, downstream or absent (treeless) relative to a single building using large-eddy simulation, this study provides detailed insights into the sensitivity of flow dynamics to the positioning of the vegetation. Upstream vegetation more significantly disrupts the flow patterns around the building obstacle, altering vertical wind profiles and modifying wake circulations, compared to downstream vegetation. A small shear layer developed at the plant top for upstream vegetation markedly influences turbulent kinetic energy (TKE) on both the leeward and windward sides of the building, shifting the inflection point in vertical TKE profiles by up to 0.13H. By contrast, smaller tree-building separations lead to an effective merging of their aerodynamic profiles, whereas larger separations confine the streamwise breadth of turbulent fluxes, amplifying flux exchanges in the spanwise direction. Spectral analyses reveal that upstream vegetation consistently results in higher power spectral densities of the streamwise turbulence in the residential area than downstream vegetation. While small-scale spanwise velocity fluctuations are found to be comparably energetic at the building's windward side for upstream vegetation, the power becomes substantially concentrated on large-scale eddies in the building wake region, providing specific insights into modulating turbulent eddy motions within the residential zone.
Improved Gaussian basis sets for norm-conserving 4f-in-core pseudopotentials of trivalent lanthanides (Ln = Ce–Lu)
Authors: Lu Jun-Bo , Zhang Yang-Yang , Jiang Xue-Lian , Ye Lian-Wei , Li Jun
Published: October 2024

The first-principles quantum chemical computations often scale as Nk (N = basis sets; k = 1–4 for linear scaling, Hartree–Fock or density functional theory methods), which makes the development of accurate pseudopotentials and efficient basis sets necessary ingredients in modeling of heavy elements such as lanthanides and actinides. Recently, we have developed 4f-in-core norm-conserving pseudopotentials and associated basis sets for the trivalent lanthanides [Lu et al., J. Chem. Theory Comput. 19, 82–96 (2023)]. In the present paper, we present a unified approach to optimize high-quality Gaussian basis sets for modeling and simulations of condensed-phase systems. The newly generated basis sets not only capture the low total energy and fairly reasonable condition number of overlap matrix of lanthanide-containing systems, but also exhibit good transferability and reproducibility. These advantages ensure the accuracy of the basis sets while avoiding linear dependency concern of atom-centered basis sets. The performance of the basis sets is further illustrated in lanthanide molecular and condensed-phase systems by using Gaussian-plane wave density functional approach of CP2K. These new basis sets can be of particular interest to model structurally complicated lanthanide molecules, clusters, solutions, and solid systems.
Alternative and simple method to determine the refractive index of human dentin
Authors: Márquez-Islas Roberto , Mendiola-Rojas Diego , Pérez-Pacheco Argelia
Published: October 2024

Determining a substance’s refractive index (RI) is of great importance in a wide variety of disciplines, such as chemistry, biomedicine, engineering, and optics, to name just a few. This work utilizes critical-angle reflectometry to measure the refractive index of dentin, a biological tissue characterized by its high RI and complex structure. We fabricated a hollow semicircular prism and filled it with bromonaphthalene (1-B), allowing us to measure RIs up to 1.65. We used 5 tooth samples with exposed dentin and a laser diode beam (λ = 650 nm) incident on interface 1-B/Dentine; the reflectance curve was measured from 60° to 75°. The critical angle is determined, and dentin RI is calculated. The real part of the calculated dentine’s RI coincided well with those determined by other more expensive and specialized techniques with high technical support.
Posterior comparison of model dynamics in several hybrid turbulence model forms
Authors: Towery Colin A. Z. , Sáenz Juan A. , Livescu Daniel
Published: October 2024

Hybrid turbulence models that can accurately reproduce unsteady three-dimensional flow physics across the entire range of grid scales and turbulence dynamics from Reynolds-averaged Navier–Stokes (RANS), through large-eddy simulation (LES), down to direct numerical simulations (DNS) are of increasing interest to the turbulence modeling community. However, despite decades of research and development, the basic tasks of eliminating poor-performing hybrid RANS-LES models and accelerating adoption of superior models through well-designed validation and verification have yet to occur. As a step in this direction, in this work we evaluate thirteen different hybrid RANS-LES models via systematic grid refinement of decaying homogeneous isotropic turbulence. We further derive a novel mathematical framework for assessing the energy partitioning dynamics of each Hybrid RANS-LES model, wherein model-to-model variations in energy partitioning can be interpreted as different feedback mechanisms operating on a low-dimensional nonlinear dynamical system. We found that model forms similar to the flow simulation methodology—also often termed very-large eddy simulation—are dynamically inconsistent with DNS at all resolutions. Additionally, we found a strong dynamical similarity in the feedback mechanisms of all models related to detached eddy simulation and partially averaged Navier–Stokes that is inherent to their general model forms.
Structure and dynamics of the near-surface water layer under conditions of natural convection
Authors: Kupriyanova A. E. , Gritsenko V. A.
Published: October 2024

A series of laboratory and numerical experiments have been performed to study the process of the surface water cooling. The process of the submergence of an ensemble of jets (a thermal-like structure) or a negative buoyancy flux was recorded using digital cameras (∼2 and 10 Hz). Quantitative estimates of the structure and dynamical features of the initial phase of the submergence of a density front of the ensemble of jets were obtained. These estimates were compared with the previous results of the study of individual thermals. It was found that the deepening velocity is characterized by the nonlinear dependence from the submergence depth in time of both the thermals and the density front of the ensemble. The numerical calculations also showed nonlinearity in this dependence. The process of submergence of the density front was divided into three stages, which were described for the first time. The deepening velocity of the density front of the ensemble of jets was ∼0.15 cm/s. The results are qualitatively consistent with the theoretical estimates of the evolution of the free convection. The observed laboratory flows have the laminar nature of convective movements (Reynolds numbers ranging from 3 to 60). A geometric model was proposed to describe linear quantity of both the thermal and jet. It was shown that the effects of turbulence on the seawater measurements were caused externally and not related to the process of the surface water cooling. Thus, it is assumed that either thermal or saline turbulence dominates over free convection conditions. This conclusion has an important role in the study of the heat exchange process in ocean models.
Study on the secondary flow in T-shaped pipe with different outlet surfaces
Authors: Yang Yuqi , Xu Zhengchao , Chen Siyu , Zhang Haipeng , Fu Yuequn , Liu Siqi , Mei Shuxing , Lv Hang
Published: October 2024

The flow within different cross sections of T-shaped pipes is analyzed using experimental measurements using particle image velocimetry technology and simulation modeling at different fluid velocities and outlet diameters. The study shows that the flow within the pipes predominantly exhibits multiple vortex patterns, with the evolution of the vortex patterns at different cross sections showing similar patterns and some degree of periodicity. It is also found that as the pipe diameter increases, the flow pattern in the main pipeline is relatively stable, although vortices form on the underside of the outlet pipe walls. Conversely, if the pipe diameter is smaller, vortices will not form within the outlet pipe, and the vortex patterns within the blind pipe will be unstable. In particular, as the velocity increases and the diameter of the outlet pipe decreases, the period of the vortex oscillation shortens. The research establishes a numerical equation relating the dominant frequency of vortex oscillations to the velocity and outlet pipe diameter, further demonstrating the mathematical relationship between the three in the outlet pipe.
Wake-induced vibration of ultra-long suspenders adjacent to bridge tower
Authors: Gao Weijie , Tao Tianyou , Wang Hao
Published: October 2024

The tower wake usually induces large-amplitude vibrations in adjacent suspenders of a long-span suspension bridge. In order to interpret the underlying mechanism of the significant wake-induced vibrations of ultra-long suspenders, the wake-induced vibration characteristics of tandem suspenders beside the bridge tower are investigated using computational fluid dynamics based simulation. First, the computational model of the bridge tower and suspenders is established. Subsequently, the effect of tower wake on suspender vibration is analyzed considering the inflow velocity and relative position between the tower and suspenders. Based on the proper orthogonal decomposition (POD), the flow characteristics behind the tower and around the suspenders are investigated, and the governing mechanism of wake-induced vibrations of the suspenders is revealed ultimately. The results indicate that the wake-induced vibration of the suspender exhibits a lock-in phenomenon with large cross-wind amplitudes at specific incoming wind velocities. The wind loads on the suspender in both along-wind and cross-wind directions exhibit components with frequencies that are multiples of the vortex shedding frequency. The flow field can be accurately constructed using the first four POD modes with the largest energy. The symmetric POD modes are the primary components that contribute to the significant wake-induced vibrations of the suspenders.
Low-symmetry layered semiconductor In2Te5 for promising polarization-sensitive photodetector
Authors: Cheng Jiaxin , Yuan Guohao , Wang Weike , Deng Pufan , Zhang Hanyang , Yin Yanling , Zhou Weichang , Peng Yuehua , Liu Ziran , Tang Dongsheng
Published: October 2024

Low-symmetry two-dimensional (2D) materials have attracted significant attention for polarization-sensitive photodetection due to the optoelectronic anisotropy. Here, we demonstrated the strong in-plane anisotropy of In2Te5 through electron density distribution calculations based on density functional theory and developed a polarization-sensitive photodetector. The photodetector shows a responsivity of 171.16 mA/W and a response time of 0.42 s under visible light illumination. Additionally, it presents a polarization-sensitive photoresponse with a dichroic ratio of 1.34. Our work reveals the anisotropic optoelectronic properties of In2Te5, potentially stimulating research interest in Group III-VI 2D materials (Pentatelluride M2Te5, M = Al, Ga, In, etc.).
Nitride spacer aided 0.15 μm AlGaN/GaN HEMT fabrication with optimized gate patterning process
Authors: Lv Beibei , Zhang Lixing , Mo Jiongjiong
Published: October 2024

I-line stepper is widely used in large scale device manufacturing with limited achievable critical dimension by itself. With the aid of the spacer sidewall, the critical dimension can be further shrunk down. Spacer sidewall aided process necessitates an additional deposition-etching process, which inevitably results in process related damage under the gate. This paper proposes an optimized spacer sidewall aided gate patterning procedure for 0.15 μm GaN High Electron Mobility Transistors (HEMTs) fabrication. The process is proved to be effective in improving device performance compared to conventional sidewall process by keeping first Si-rich SiN passivation layer integrity at the gate edge. Interface trap density (Dit) and mobility were extracted for both conventional sidewall process and the optimized one with different passivation layers at the gate edge, demonstrating a lower Dit and higher mobility using the optimized process with enhanced device performances, such as higher current, breakdown voltage, and stress state characteristics, compared to the conventional process, which is promising for mass production of 0.15 μm GaN HEMTs.
Molecular dynamics analysis of the crossover phenomenon in supercritical carbon dioxide
Authors: Li Sina , Deng Wei , He Sihong , Lau Kwun Ting , Ji Dongxu , Zhang Xuan , Zhao Jiyun
Published: October 2024

Supercritical carbon dioxide (SCO2) finds widespread applications but its complex phase behavior near and beyond the critical point remains unclear. In this work, extensive focus has been invested in the thermodynamic transitions of SCO2 from a microscopic perspective. It is revealed that both the radial distribution function and structure factor exhibit apparent crossover phenomena as temperature changes. Remarkably, our findings demonstrate an unprecedented agreement between the predicted crossover points using different functions and the experimental Frenkel Line (FL), with a deviation of merely 5.6%. By applying the same method, the FL crossover region is successfully predicted and extended up to an impressive pressure of 200 MPa. Notably, this prediction is a valuable guide in narrowing down the temperature range for further experimental tests. Concurrently, a correlation between the coordination number and the FL is discovered. Overall, our research provides compelling evidence supporting the FL as thermodynamic transitions between the gas-like and liquid-like regions and presents a novel and reliable approach for identifying the FL, which offers valuable theoretical insights into the phase behavior in the supercritical state.
Surface roughness effects in a transonic axial flow compressor operating at near-stall conditions
Authors: Godse Prashant B. , Akolekar Harshal D. , Pradeep A. M.
Published: October 2024

Surface roughness is a major contributor to performance degradation in gas turbine engines. The fan and the compressor, as the first components in the engine's air path, are especially vulnerable to the effects of surface roughness. Debris ingestion, accumulation of grime, dust, or insect remnants, typically at low atmospheric conditions, over several cycles of operation are some major causes of surface roughness over the blade surfaces. The flow in compressor rotors is inherently highly complex. From the perspective of the component designers, it is, thus, important to study the effect of surface roughness on the performance and flow physics, especially at near-stall conditions. In this study, we examine the effect of surface roughness on flow physics such as shock-boundary layer interactions, tip and hub flow separations, the formation and changes in the critical points, and tip leakage vortices among other phenomena. Steady and unsteady Reynolds Averaged Navier Stokes calculations are conducted at near-stall conditions for smooth and rough National Aeronautics and Space Administration rotor 67 blades. Surface streamlines, Q-criterion, and entropy contours aid in analyzing the flow physics qualitatively and quantitatively. It is observed that from the onset of stall, to fully stalled conditions, the blockage varies from 21.7% to 59.6% from 90% span to the tip in the smooth case, and from 40.5% to 75.2% in the rough case. This significant blockage, caused by vortex breakdown and chaotic flow structures, leads to the onset of full rotor stall.
Transient microstructural behavior of methanol/n-heptane droplets under supercritical conditions
Authors: Wang Zhanyuan , Zhao Wanhui , Wei Haiqiao , Shu Gequn , Zhou Lei
Published: October 2024

Supercritical fluids exist widely in nature and have enduringly attracted scientific and industrial interest. In power systems like liquid rocket engines, fluids undergo the trans-critical process transferred from the subcritical state to the supercritical state, and the phase change process exhibits different features distinguished from subcritical evaporation. In this work, we conducted a series of molecular dynamics studies on the behavior of methanol (MeOH), n-heptane (C7), and binary C7/MeOH droplets under supercritical nitrogen environments. The emphasis is on clarifying the transient characteristics and physical origins of the trans-critical evolution of droplets. During the trans-critical process, droplets are found to experience an unstable period without a spherical shape, where the droplet diameter no longer decreases, violating the traditional d2-law rule. The occurrence of nonspherical droplets is related to the microstructural behavior of trans-critical droplets. Two types of microscopic structures within the droplet are identified: large-scale thermally induced clusters for long-chain C7 and hydrogen-bond connected network-like structures for MeOH, which contains hydroxyl (–OH) groups. Based on these findings, the mechanism behind the evolution of trans-critical droplets is illustrated. Finally, we determine the boundary of ambient conditions in the form of dimensionless expressions Tr−1=a(pr−1)−b, which dictate whether droplets can maintain a spherical shape during the trans-critical process.
Interaction behavior between hydraulic fractures and interface in coal-rock complex rock layer: Experimental study and application exploration
Authors: Li Bo , Shi Zhen , Zhang Junxiang , Wang Nannan , Li Qinghai , Li Feng
Published: October 2024

To achieve long-term and efficient gas extraction in soft, low-permeability coal seams, this study conducted hydraulic fracturing experiments on coal-rock complexes under true triaxial conditions. The pattern of hydraulic fractures (HFs) was reconstructed based on the fractal dimension concept. The results indicate that the tendency of the complex rock layers to initiate fractures toward the coal weakens the trend of increasing fracture initiation pressure with rising geostress. When HFs interact with the interface, the extension pressure significantly decreases. With the lateral pressure coefficient decreasing, HFs tend to extend toward the coal and be captured by the interface, transitioning from a single-wing to a double-wing shape and approaching a symmetrical conjugate state. Only when the vertical principal stress is sufficiently large can HFs separate from the interface. Based on the derived distribution function of induced stress in the coal-rock matrix around the HFs, the displacement conditions of the coal, rock, and interface were examined. The interaction process of rock layer HFs and the interface was divided into three stages: deflection, capture, and separation. The applicability of this study to high-gas soft coal seams was discussed, and a gas management plan involving roof fracturing and full-period extraction was proposed, with the aim of providing a theoretical foundation for the co-extraction and efficient utilization of coal and gas in mines.
Influence of back pressure adjustment of porous media on cavity flow noise control
Authors: Li Bo , Zhou Qingqing , Yuan Xianxu , Su Hongmin , Guo Qilong
Published: October 2024

Control of self-sustained oscillation and noise reduction poses a significant challenge. The present study employs Implicit Large Eddy Simulation at a Mach number of 0.85 to investigate the influence of a porous cavity floor on flow dynamics. By substituting the solid floor with porous media, the fundamental pressure–velocity relationship within the medium is established according to Darcy's law. Findings reveal marked suppression of wall pulsations, accompanied by a 10 dB decrease in sound pressure levels. The porous medium induces blowing and suction effects, effectively modulating large-scale re-circulation and mitigating shear layer instability, thereby approximating free mixing layer characteristics and suppressing cavity flow oscillations. At an optimized porosity for maximum noise reduction, altering back pressure at the cavity floor induces a transition in the local flow regime from suction-dominated to blowing-dominated state. Excessive reduction of back pressure promotes suction; conversely, increased pressure intensifies blowing, further attenuating feedback mechanisms and enhancing noise reduction. To explore noise reduction mechanisms, mode decomposition analyses demonstrate the efficacy of porous media in disrupting large-scale coherence structures within shear layer and redistributing energy from dominant modes to a broader frequency spectrum that engages smaller flow structures. This energy reallocation mechanism contributes to the mitigation of cavity flow noise and deepens insights into the role of porous media in flow modulation and noise control.
Surface plasmon resonance enhanced terahertz spin current emission in Au nanoparticles/ferromagnet thin film heterostructure
Authors: Zhang Lei , Zeng Xiaoxue , Zhang Dainan , Wen Tianlong , Zhong Zhiyong , Zhang Huaiwu , Jin Lichuan
Published: October 2024

We present a design of an ultrafast spin current emitter utilizing the Au nanoparticles/Co/Pt heterostructures, which facilitate significant enhancement in terahertz radiation. Using Au nanoparticles synthesized by thermal annealing and embedded in Co/Pt bilayers, we show that the Au nanoparticles fulfill surface plasmon resonance conditions under the illumination of femtosecond laser pulses, and enhanced terahertz spin currents are generated in the Co thin film. The terahertz signal amplitude of Au nanoparticles/Co/Pt sample exhibits an enhancement of 70% and 45% compared to that observed in Au thin film/Co/Pt and Co/Pt samples, respectively. By integrating experimental analysis and numerical calculations, we ascribe the enhancement of terahertz emission amplitude to the contribution of spin current generated by surface plasmon resonance in the Co thin film, which may result from the magnetization enhancement induced by surface plasmon-excited electromagnetic fields at the Au nanoparticles/Co interface, and the plasmon-induced spin current density is approximately 1 × 1029 electrons s−1 m−2. This plasmon-induced spin current establishes a connection between the fields of plasmonic and spintronic physics, thereby promoting the development of spintronic terahertz emitters.
Scalar mixing and entrainment in an axisymmetric jet subjected to external turbulence
Authors: Kohan Khashayar F. , Gaskin Susan J.
Published: October 2024

The present study aims to understand the process of turbulent entrainment into a jet, as affected by background turbulence, using scalar statistics. Planar laser-induced fluorescence was employed to capture the orthogonal cross sections of the jet at a fixed downstream station with varying background turbulence intensities and length scales. The conditional scalar profiles revealed that the thickness of the scalar turbulent/turbulent interface is greater than that of the traditional turbulent/non-turbulent interface, and the interfacial thickness is an increasing function of the background turbulence intensity. Although nibbling remains the primary entrainment mechanism in the far field, increased occurrence of concentration “holes” within the interfacial layer in the presence of ambient turbulence suggests a more significant role of large-scale engulfment in the turbulent/turbulent entrainment process (although still below 1% of the total mass flux). Enhanced contribution of the area of detached jet patches (i.e., “islands”) to that of the main jet is hypothesized to be evidence of intense detrainment events in the background turbulence. This can potentially contribute to a reduced net entrainment into the jet, which manifests as less negative values of scalar skewness within the jet core.
Visualizing liquid distribution across hyphal networks with cellular resolution
Authors: Clark Amelia J. , Masters-Clark Emily , Moratto Eleonora , Junier Pilar , Stanley Claire E.
Published: October 2024

Filamentous fungi and fungal-like organisms contribute to a wide range of important ecosystem functions. Evidence has shown the movement of liquid across mycelial networks in unsaturated environments, such as soil. However, tools to investigate liquid movement along hyphae at the level of the single cell are still lacking. Microfluidic devices permit the study of fungal and fungal-like organisms with cellular resolution as they can confine hyphae to a single optical plane, which is compatible with microscopy imaging over longer timescales and allows for precise control of the microchannel environment. The aim of this study was to develop a method that enables the visualization and quantification of liquid movement on hyphae of fungal and fungal-like microorganisms. For this, the fungal–fungal interaction microfluidic device was modified to allow for the maintenance of unsaturated microchannel conditions. Fluorescein-containing growth medium solidified with agar was used to track liquid transported by hyphae via fluorescence microscopy. Our key findings highlight the suitability of this novel methodology for the visualization of liquid movement by hyphae over varying time scales and the ability to quantify the movement of liquid along hyphae. Furthermore, we showed that at the cellular level, extracellular movement of liquid along hyphae can be bidirectional and highly dynamic, uncovering a possible link between liquid movement and hyphal growth characteristics. We envisage that this method can be applied to facilitate future research probing the parameters contributing to hyphal liquid movement and is an essential step for studying the phenomenon of fungal highways.
A data-driven approach to analyze bubble deformation in turbulence
Authors: Calado Andre , Capuano Francesco , Balaras Elias
Published: October 2024

Bubble deformation and breakup from turbulence is present in many engineering applications and in nature, yet the physical mechanisms still remain poorly understood. Depending on the local turbulence intensity or Weber number, a bubble may either deform without breakup, suffer a violent breakup, or exhibit a resonant behavior, where the turbulent eddies excite the bubble's natural frequencies. Recent studies have used spherical harmonic decomposition to analyze bubble interaction with turbulence, quantifying the deformation energy of each eigenmode. However, this approach is only applicable for small levels of deformation (linear regime), while the bubble shape remains close to a sphere. In the present work, we present a novel data-driven approach combining large deformation diffeomorphic metric mapping and proper orthogonal decomposition, which is more robust for large deformations. The method is tested on a set of validation cases and applied to turbulent bubble deformation cases obtained from direct numerical simulations data.
Third party interventions promote cooperation on the interdependent networks: A perspective based on prospect theory
Authors: Wu Yu’e , Li Zhiqiang , Liu Zeyun , Cui Bowei , Yin An’ran
Published: October 2024

Third-party intervention is a beneficial means to alleviate conflicts and promote cooperation among disputants. The decision-making of disputants is closely related to the intensity of the impact of third-party intervention on their profits. Actually, disputants often decide whether to adopt cooperative strategies based on their own perceived rather than actual gains or losses brought about by third-party intervention. We, therefore, introduce prospect theory to explore the formation and maintenance of cooperation in a system composed of third parties and disputants, which, respectively, constitute two sub-networks of the interdependent networks. Both interveners and disputants participate in a prisoner’s dilemma game, and the third-party intervener will pay a certain price to impose certain punishments on the defectors of the disputed layer. The simulation results show that the introduction of third-party intervention based on the prospect theory alleviates the conflicts in the dispute layer and promotes cooperation among disputants, which indicates that third parties such as governments or organizations should appropriately consider the risk attitudes of disputants when mediating their conflicts. The level of cooperation at the dispute layer is inversely proportional to the intervention cost and directly proportional to the intervention intensity. Our research may shed some new light on the study of the evolution of cooperation under third-party intervention.
A data-driven method for fast predicting the long-term hydrodynamics of gas–solid flows: Optimized dynamic mode decomposition with control
Authors: Li Dandan , Zhao Bidan , Lu Shuai , Wang Junwu
Published: October 2024

Data-driven methods are of great interest in studying the hydrodynamics of gas–solid flows. In this paper, we developed an optimized dynamic mode decomposition with control (DMDc) method for long-term and fast prediction of one physical field with the aid of another physical field. Using the computational fluid dynamics-discrete element method (CFD-DEM) simulation results as the benchmark, the prediction ability of the standard DMDc method and the optimized DMDc method is evaluated. It was shown that the optimized DMDc method is superior when the order of magnitude of the predicted data is much larger than that of the auxiliary data, which cannot be addressed by using scaled or dimensionless data, for instance, the prediction of gas pressure with the aid of solid volume fraction; on the other hand, both DMDc and optimized DMDc methods can reasonably predict the long-term behavior of gas–solid flows, when the magnitude of the elements of the predicted field is comparative to that of the auxiliary field. This study proposes a fast and relatively accurate method for predicting the hydrodynamics of gas–solid flows with the aid of a known field.
Electron-acoustic solitary waves via suprathermal populations in Saturn's magnetosphere: Bifurcation, sensitivity, and stability analysis
Authors: Ibrahim I. E. , Abdel-Gawad H. I. , Al-Dossari M. , EL-Gawaad N. S. Abd
Published: October 2024

Cassini and Voyager space missions observed non-thermal electron populations (with varying characteristics) in Saturn's magnetosphere, which can be correctly described using kappa distributions. Based on these observations, our objective is to inspect the evolution of electron-acoustic solitary waves (EASWs) within Saturn's magnetosphere. The propagation of weakly nonlinear (EASWs) in a collisional plasma system comprising a cold electron fluid, hot electrons following a kappa distribution, and stationary ions is investigated. By employing the reductive perturbation technique, the Korteweg–de Vries Burgers (KdV–B) equation is derived. An exact solution of the KdV–B equation, with a conformable time-derivative, is found using the unified method. It is observed that plasma current-induced collision between electrons and ions leads to remarkable dissipation, generating EASWs. Furthermore, when studying the sensitivity of the system, the appearance of a positive potential is depicted as external forces vanish, which may be due to stationary ions. Additionally, bifurcation, stability, and significant influence of plasma characteristics are considered.
Integration of deep learning and computational fluid dynamics for rapid aerodynamic force prediction of compressor blades
Authors: Niu Yan , Zhao Kainuo , Yang Yuejuan , Yao Minghui , Wu Qiliang , Bai Bin , Ma Li
Published: October 2024

The distribution of flow fields around compressor blades is crucial for the performance and reliability of aircraft engines. To effectively obtain aerodynamic loads, this study combines deep learning with computational fluid dynamics (CFD) to develop an efficient aerodynamic prediction model. Initially, CFD is used to acquire detailed flow field data for the blade surface and its surrounding environment. Subsequently, a distance field parameterization method is applied to process the blade geometry, and deep learning models are used to capture the complex relationship between blade geometry and aerodynamic parameters with high precision. The results indicate that the proposed model can predict aerodynamic loads within seconds with a mean squared error of less than 2%. Compared to traditional parameterization methods and other deep learning approaches, this model exhibits higher accuracy. The findings highlight the effectiveness of integrating deep learning with CFD to enhance aerodynamic predictions and provide a promising approach for future aerodynamic modeling research.
Multi-region coupling computational fluid dynamics simulation of the underground compressed air energy storage process
Authors: Huang Yuhui , Chen Xiaoguo , She Xiao , Zhao Jian , Dong Weijian
Published: October 2024

Compressed air energy storage (CAES) in underground spaces is a common method for addressing the instability of renewable energy generation. As the construction and testing of CAES systems are often of high cost, the numerical simulation which offers a more efficient and low-cost research method can provide a better alternative to research the process. In this study, a numerical simulation model has been developed to describe the air movement within the CAES process. Specifically, the study focuses on two different types of motion: air compressible flow within the cavern and air porous flow in the surrounding rock. Using OpenFOAM, a multi-region coupling solver has been developed to address the different governing equations for these two types of motion, and couples pressure, velocity, and temperature at the boundaries. The developed solver is used to simulate a field test of a CAES system. The numerical simulation results closely match the experimental data, verifying the reliability of the solver. Moreover, the solver can achieve multi-region flow simulations that are previously unattainable, resulting in more accurate simulations. Simulations have also been conducted to analyze various working conditions, including different rock permeability, porosity, and air injection mass rates. The results show that different conditions significantly affect air pressure, leakage rate, temperature, and flow field changes within the cavern. These simulation results and the underlying mechanisms have been analyzed to provide reference and technical support for site selection, construction, and operational strategies of CAES systems in underground spaces.
Three-dimensional particulate volume fraction reconstruction in the fluid based on the Lambert–Beer physics information neural network
Authors: Wang Qianlong , Qian Yingyu
Published: October 2024

The measurement of particle volume fraction in flow fields is of great significance in scientific research and engineering applications. As one of the particle detection techniques, the light extinction method is widely used in measuring nano-particles volume fraction in flow fields due to its simplicity and non-contact nature. In particular, in complex reactive flow fields like combustion reactions, the volume fraction of soot particulate and other particles can be accurately measured and reconstructed via the light extinction method that based on the Beer–Lambert law. This is crucial for exploring combustion phenomena, understanding their internal mechanisms, and reducing pollutant emissions. However, due to the enormous computational burden, current algebra reconstruction techniques struggle to achieve high-precision three-dimensional (3D) reconstruction of particles. Therefore, this paper originally proposes a 3D reconstruction algorithm based on the Beer–Lambert law physical information neural networks (LB-PINNs). By incorporating physical information as constraints into the particle reconstruction process, it is possible to achieve high-precision 3D reconstruction of particles in complex flow field environments with low computational cost. Meanwhile, to address the trade-off issues of reconstruction accuracy and smooth noise resistance in previous reconstruction algorithms, i.e., Tikhonov regularization, this paper employs dynamically adjusted regularization parameters in the LB-PINN algorithm. This approach ensures smooth noise-resistant processing while maintaining reconstruction accuracy, significantly reducing computation time and resource consumption. According to the experimental results, LB-PINNs demonstrate superior performance compared to previous reconstruction algorithms when reconstructing the soot volume fraction in complex reacting flow fields, i.e., combustion flame scenarios.
Eddy viscosity enhanced temporal direct deconvolution model for temporal large-eddy simulation of turbulent channel flow
Authors: Fan Boyu , Wang Yunpeng , Yuan Zelong , Wang Jianchun
Published: October 2024

In this work, a novel eddy viscosity enhanced temporal direct deconvolution model (TDDM) is proposed for temporal large-eddy simulation (TLES) of turbulent channel flow at large filter widths. To improve the accuracy of the constant eddy viscosity (CEV) model, particularly in the near-wall region, a damping function is incorporated to refine its performance. Moreover, a spatial filtering strategy is introduced to reduce the aliasing errors associated with the computation of subfilter-scale (SFS) stress, thereby enhancing numerical stability. In the a posteriori study, the accuracy of the CEV model is assessed comprehensively by comparing the TLES results with corresponding temporally filtered direct numerical simulation data. The results demonstrate that the CEV-enhanced TDDM provides accurate predictions across various statistical properties of velocity, instantaneous flow structures, kinetic energy spectra, and SFS energy fluxes. The coefficient sensitivity analysis of the CEV model reveals that the model coefficient significantly influences low Reynolds number flows, while its impact on high Reynolds number flows is relatively small. TLES on coarse grids demonstrate that the CEV-enhanced TDDM exhibits strong robustness and accuracy at different grid resolutions. Additionally, the CEV-enhanced TDDM in high Reynolds number flows is stable and accurate at remarkably large filter widths.
Erosion assessment and anti-erosion optimization design for Francis turbine
Authors: Sun Longgang , Zhang Qian , An Dongdong , Xu Zhuofei , Sun Shuaihui , Guo Pengcheng
Published: October 2024

Sediment erosion poses a significant challenge for hydraulic turbines in sediment-laden rivers. This paper investigates the erosion patterns in high-head Francis turbines using numerical simulations. It analyzes how sediment concentration, particle size, and operating conditions affect wear on turbine components. The results identify the trailing edges of the guide vanes, the intersection of runner blade trailing edge, and runner band as primary erosion zones. Higher sediment concentrations increase erosion intensity and extend the erosion range upstream. Small particles uniformly affect both pressure and suction sides of the blades, while larger particles concentrate erosion near the runner band trailing edges. The flow rate has a greater impact on runner blade erosion than water head, with lower flow rates reducing pressure side erosion but initially increasing, then decreasing suction side erosion. Additionally, the study proposes a multi-objective, multi-condition optimization design method that balances erosion resistance and energy efficiency. The optimized runner reduces the maximum erosion rate by 23.91% while limiting the weighted efficiency loss to under 0.1%. The improved runner design reduces high erosion areas on both blade sides, particularly decreasing particle impact speeds near the trailing edges. Sensitivity analysis reveals a trade-off between minimizing erosion and maintaining hydraulic efficiency, highlighting the importance of span height at 75% for controlling erosion. Changes in blade circumference angle generally reduce erosion but may also lower efficiency. Overall, this research demonstrates a successful reduction in Francis turbine erosion while preserving hydraulic efficiency, offering valuable guidance for anti-erosion turbine design in sediment-heavy environments.