bluuebunny/crossref_metadata_2025 huggingface dataset:
Adaptable reservoir computing: A paradigm for model-free data-driven prediction of critical transitions in nonlinear dynamical systems
Authors: Panahi Shirin , Lai Ying-Cheng
Published: May 2024

A problem in nonlinear and complex dynamical systems with broad applications is forecasting the occurrence of a critical transition based solely on data without knowledge about the system equations. When such a transition leads to system collapse, as often is the case, all the available data are from the pre-critical regime where the system still functions normally, making the prediction problem challenging. In recent years, a machine-learning based approach tailored to solving this difficult prediction problem, adaptable reservoir computing, has been articulated. This Perspective introduces the basics of this machine-learning scheme and describes representative results. The general setting is that the system dynamics live on a normal attractor with oscillatory dynamics at the present time and, as a bifurcation parameter changes into the future, a critical transition can occur after which the system switches to a completely different attractor, signifying system collapse. To predict a critical transition, it is essential that the reservoir computer not only learns the dynamical “climate” of the system of interest at some specific parameter value but, more importantly, discovers how the system dynamics changes with the bifurcation parameter. It is demonstrated that this capability can be endowed into the machine through a training process with time series from a small number of distinct, pre-critical parameter values, thereby enabling accurate and reliable prediction of the catastrophic critical transition. Three applications are presented: predicting crisis, forecasting amplitude death, and creating digital twins of nonlinear dynamical systems. Limitations and future perspectives are discussed.
Unleashing the power of artificial intelligence in phonon thermal transport: Current challenges and prospects
Authors: Hu Ming
Published: May 2024

The discovery of advanced thermal materials with exceptional phonon properties drives technological advancements, impacting innovations from electronics to superconductors. Understanding the intricate relationship between composition, structure, and phonon thermal transport properties is crucial for speeding up such discovery. Exploring innovative materials involves navigating vast design spaces and considering chemical and structural factors on multiple scales and modalities. Artificial intelligence (AI) is transforming science and engineering and poised to transform discovery and innovation. This era offers a unique opportunity to establish a new paradigm for the discovery of advanced materials by leveraging databases, simulations, and accumulated knowledge, venturing into experimental frontiers, and incorporating cutting-edge AI technologies. In this perspective, first, the general approach of density functional theory (DFT) coupled with phonon Boltzmann transport equation (BTE) for predicting comprehensive phonon properties will be reviewed. Then, to circumvent the extremely computationally demanding DFT + BTE approach, some early studies and progress of deploying AI/machine learning (ML) models to phonon thermal transport in the context of structure–phonon property relationship prediction will be presented, and their limitations will also be discussed. Finally, a summary of current challenges and an outlook of future trends will be given. Further development of incorporating AI/ML algorithms for phonon thermal transport could range from phonon database construction to universal machine learning potential training, to inverse design of materials with target phonon properties and to extend ML models beyond traditional phonons.
Interstage transmission and differential analysis of pressure fluctuations in multistage centrifugal pump-as-turbine
Authors: Li Xiaojun , Zhou Houkuo , Wei Zhicong , Zhu Zuchao
Published: May 2024

Pumps as turbines (PATs) are used in petroleum and chemical industries to recover high-pressure residual energy. Multistage PATs allow for a wider energy recovery interval and wider range of applications. However, because multistage centrifugal pumps were not originally designed for turbine conditions, complex pressure fluctuations occur, impacting the stable operation and performance of multistage PAT. Pressure fluctuation is essentially a wave, and by analogy with the wave intensity definition, pressure fluctuations were quantified using the pressure wave energy flow density, and the pressure fluctuation patterns at different stages were investigated. The findings reveal significant differences in the intensity of pressure fluctuations at different locations within the multistage PAT. Specifically, the pressure fluctuation intensity is significantly higher from the second to the final stage, compared to the first stage. The difference in inlet flow conditions is the main reason for this difference in pressure fluctuations between stages. The inlet inflow from the second to the final stage is subject to rotational effects that exacerbate the difference in pressure fluctuation intensity between stages. Pressure fluctuations are found to be negatively related to the distance from the source of fluctuations and positively related to the flow state. Different flow conditions and interaction regions of the impeller affect the distribution of pressure fluctuation intensity and the distribution of pressure fluctuation energy across different frequency domains within the guide vanes. The main source of fluctuations in the shaft frequency and four times the shaft frequency is the impeller inlet interaction region, whereas the fluctuations in the blade passing frequency originate from the impeller outlet interaction region. This paper provides a reference for improving the stable operation of multistage PATs.
Numerical simulations of bio-inspired approaches to enhance underwater swimming efficiency
Authors: Kumar Rahul , Padhee Srikant S. , Samanta Devranjan
Published: May 2024

The present study discusses the numerical simulation results of swimming similar to manta rays. The complex three-dimensional kinematics of manta rays were implemented to unravel the intricacies of its propulsion mechanisms by using the discrete vortex method (DVM). The DVM replaces the requirement for a structured grid across the computational domain with a collection of vortex elements. This method simplifies grid generation, especially for intricate geometries, resulting in time and effort savings in meshing complex shapes. By modeling the pectoral fins with discrete panels and utilizing vortex rings to represent circulation and wake, the study accurately computes the pressure distribution, circulation distribution, lift coefficient, and thrust coefficient of the manta ray. This study focuses on the modulation of aerodynamic performance by altering the span length and the length change ratio during the downstroke and upstroke motion (SV). The manta ray's three-dimensional vortex configurations comprise a combination of vortex rings, vortex contrails, and horseshoe vortices. Analysis of the three-dimensional vortex structure indicates the presence of multiple vortex rings and horseshoe vortex rings at higher SV values, while adequate formation of horseshoe vortices is not observed at lower SV values. In terms of propulsive performance, both lift and thrust increase with SV, while the propulsive efficiency demonstrates its peak at SV = 1.75. The analysis reveals that at higher SV values, the net thrust generated primarily originates from the tip of the fins. Moreover, the study illustrates a significant enhancement in propulsive efficiency, particularly in association with optimal Strouhal numbers ranging between 0.3 and 0.4. The key findings of this study may be used in efficient design of agile autonomous underwater vehicles for marine exploration and surveillance applications.
Experimental and numerical study of a hollow droplet impacting on inclined solid surfaces
Authors: Nasiri Mohammad Mahdi , Tembely Moussa , Moreau Christian , Dolatabadi Ali
Published: May 2024

This study sheds light on the complex dynamics of hollow droplet impacts and highlights the unique behaviors that differentiate them from their dense counterparts. The impact dynamics of hollow droplets on surfaces at varying angles were investigated through a combination of experimental and numerical methods. Two-view imaging technique is used to capture the droplet flattening during the experimental study. A three-dimensional compressible solver is developed to model the droplet impact using the volume of fluid method to capture the liquid and gas interface. The study revealed two distinct behaviors when comparing the flattening of hollow droplets to that of dense droplets. First, a unique counter-jet formation was observed following the collision of a hollow droplet perpendicular to the surface, indicating an inherent characteristic of hollow droplet flattening. The length of this counter-jet was primarily influenced by the droplet velocity and liquid viscosity, with the perpendicular velocity component playing a key role in its size. Second, unlike dense droplets that recoil and form a dome shape upon impact on hydrophobic surfaces, hollow droplets form a donut shape due to disturbances caused by bubble rupture during spreading. These disturbances fragmented the liquid sheet, preventing the droplet from recoiling and resulting in a distinctive donut shape. On surfaces with different orientations, the hollow droplet exhibited two velocity components, where the normal component controls the counter-jet size while the tangential component induces tangential motion. The donut shape splat was also observed on surfaces with different orientations.
Basin entropy as an indicator of a bifurcation in a time-delayed system
Authors: Tarigo Juan P. , Stari Cecilia , Masoller Cristina , Martí Arturo C.
Published: May 2024

The basin entropy is a measure that quantifies, in a system that has two or more attractors, the predictability of a final state, as a function of the initial conditions. While the basin entropy has been demonstrated on a variety of multistable dynamical systems, to the best of our knowledge, it has not yet been tested in systems with a time delay, whose phase space is infinite dimensional because the initial conditions are functions defined in a time interval [−τ,0], where τ is the delay time. Here, we consider a simple time-delayed system consisting of a bistable system with a linear delayed feedback term. We show that the basin entropy captures relevant properties of the basins of attraction of the two coexisting attractors. Moreover, we show that the basin entropy can give an indication of the proximity of a Hopf bifurcation, but fails to capture the proximity of a pitchfork bifurcation. The Hopf bifurcation is detected because before the fixed points become unstable, a oscillatory, limit-cycle behavior appears that coexists with the fixed points. The new limit cycle modifies the structure of the basins of attraction, and this change is captured by basin entropy that reaches a maximum before the Hopf bifurcation. In contrast, the pitchfork bifurcation is not detected because the basins of attraction do not change as the bifurcation is approached. Our results suggest that the basin entropy can yield useful insights into the long-term predictability of time-delayed systems, which often have coexisting attractors.
The development of W waveband diffraction radiation oscillator
Authors: Xi Hongzhu , Huang Minjian , Wang Pengkang , Shu Jie
Published: May 2024

This study presents the development of a continuous wave diffraction radiation oscillator utilizing a sheet electron beam. The oscillator comprises a slow-wave system formed by double-comb gratings, an open resonant cavity consisting of a spherically curved mirror and a cylindrically curved mirror, and a sheet electron beam generated by a diode gun. A permanent magnetic focusing system stabilizes the transmission of the sheet electron beam within the slow-wave system. Through a combination of mechanical and electronic tuning, the oscillator generates stable signal output in the TEM00q mode. The oscillator's frequency tuning range spans from 87 to 97 GHz, achieving a maximum output power of 13.5 W.
Mean force emission theory for classical bremsstrahlung in strongly coupled plasmas
Authors: Kinney J. P. , LeFevre H. J. , Kuranz C. C. , Baalrud S. D.
Published: May 2024

This work presents mean force emission theory, which extends the classical theory of bremsstrahlung emission to strongly coupled plasmas. In the high-frequency limit, the theory reduces to solving for the electron trajectory during a binary collision, but where the electron–ion interactions occur through the potential of mean force. In the low-frequency limit, it uses an autocorrelation formalism that captures effects of multiple collisions and strongly correlated motion. The predictions are benchmarked by comparison with first-principles classical molecular dynamics simulations of a fully ionized hydrogen plasma in which all interactions are repulsive. The comparison shows good agreement up to Coulomb coupling strengths of Γ∼30. The theory improves upon traditional models by including strong coupling effects and systematically including the effect of multiple collisions. Furthermore, mean force emission theory provides evidence that the Drude correction factor commonly used in quantum calculations of optical quantities may not be adequate at strong coupling.
Competing conduction mechanisms for two-dimensional electron gas at LaTiO3/SrTiO3 heterointerfaces
Authors: Leng Huaqian , Xu Kunyao , Tian Hanyue , He Yongheng , Zhao Yan , Xu Minghui , Yu Xiaojiang , Breese Mark B. H. , Zhang Hui , Liu Zhengtai , Shen Dawei , Wu Xiaoqiang , Yi Jiabao , Qiao Liang
Published: May 2024

In pursuit of understanding the mechanism of two-dimensional electron gas (2DEG), artificial heterostructures based on SrTiO3 have sparked a wealth of exciting experimental and theoretical results. However, to date, the physical origin of this phenomenon still remains controversial. In our endeavor to unravel the mystery, we have synthesized a series of LaTiO3+δ/SrTiO3 films by controlling growth temperature and oxygen pressure, respectively. X-ray absorption results identify the transition of Ti ions from Ti3+ to Ti4+. It is proved that electrical transport properties in the LaTiO3/SrTiO3 film are dominated by oxygen vacancies in SrTiO3. In addition, the metallic behavior observed in the amorphous LaTiO3/SrTiO3 film suggests contributions from growth-induced donor defects to 2DEG. Our work presents direct evidence of competing conduction mechanisms for the observed 2DEG at the LaTiO3/SrTiO3 interface and highlights the important role of oxygen diffusion from the substrate SrTiO3. Meanwhile, we emphasize the significance of LaTiO3 as an oxygen scale meter to investigate interfacial properties of oxide heterostructures.
Three-dimensional internal flow evolution of an evaporating droplet and its role in particle deposition pattern
Authors: Li Jiaqi , Hong Jiarong
Published: May 2024

The internal flow within an evaporating sessile droplet is one of the driving mechanisms that lead to various particle deposition patterns seen in applications such as inkjet printing, surface patterning, and blood stain analysis. Despite decades of research, the causal link between droplet internal flow and particle deposition patterns has not been fully established. In this study, we employ a three-dimensional (3D) imaging technique based on digital inline holography to quantitatively assess the evolution of internal flow fields and particle migration in three distinct types of wetting droplets, namely water droplets, sucrose aqueous solution droplets, and sodium dodecylsulfate aqueous solution droplets, throughout their entire evaporation process. Our imaging reveals the three-stage evolution of the 3D internal flow regimes driven by changes in the relative importance of capillary flow, Marangoni flow, and droplet boundary movement during evaporation. Moreover, the migration of individual particles from their initial locations to deposition can be divided into five categories, with some particles depositing at the contact line and others inside the droplet. In particular, we observe the changing migration directions of particles due to competing Marangoni and capillary flows. We further develop an analytical model that predicts the droplet internal flow, deposition patterns, and determines the deposition mechanisms depending on their initial locations and evolving internal flow. The model, validated using different types of droplets from our experiment and the literature, can be further expanded to other Newtonian and non-Newtonian droplets, potentially serving as a real-time assessment tool for particle deposition in various applications.
Cavity-enhanced dual-comb spectroscopy with wide spectral band tuning
Authors: Tang Bocheng , Zhang Weipeng , Lu Minjian , Huang Chao , Li Yan , Wei Haoyun
Published: May 2024

Cavity-enhanced dual-comb spectroscopy holds significant research value by combining the high sensitivity of cavity enhancement and dual-comb high resolution and rapid measurement. However, due to the presence of intracavity dispersion, the insufficient coupling between the enhancement cavity and the optical frequency comb restricts the measurement bandwidth of the system, making it unable to provide abundant spectral information of the sample. To overcome this limitation, we propose a cavity-enhanced dual-comb spectroscopy with wide spectral band tuning by a single-point locking tuning scheme, which achieves a tuning capability of over 9 THz at the central wave number of 6400 cm−1. This represents a significant improvement compared to the untuned cavity-enhanced spectrum, increasing the measurable bandwidth by 2.5 times. We verified the capability of the scheme by measuring the rovibrational spectrum of CO2 in various frequency bands within the 6250–6550 cm−1 range. In each tuned frequency band, we achieved an enhancement factor of ∼950, signal-to-noise ratio (SNR > 600) in 30 s, and resolution of 250 MHz. The cavity-enhanced dual-comb spectroscopy with wide spectral band tuning holds promise for potential applications in fields such as trace gas analysis and respiratory diagnostics.
Semiclassical approaches to perturbative time-convolution and time-convolutionless quantum master equations for electronic transitions in multistate systems
Authors: Sun Xiang , Liu Zengkui
Published: May 2024

Understanding the dynamics of photoinduced processes in complex systems is crucial for the development of advanced energy-conversion materials. In this study, we investigate the nonadiabatic dynamics using time-convolution (TC) and time-convolutionless (TCL) quantum master equations (QMEs) based on treating electronic couplings as perturbation within the framework of multistate harmonic (MSH) models. The MSH model Hamiltonians are mapped from all-atom simulations such that all pairwise reorganization energies are consistently incorporated, leading to a heterogeneous environment that couples to the multiple electronic states differently. Our exploration encompasses the photoinduced charge transfer dynamics in organic photovoltaic carotenoid–porphyrin–C60 triad dissolved in liquid solution and the excitation energy transfer (EET) dynamics in photosynthetic Fenna–Matthews–Olson complexes. By systematically comparing the perturbative TC and TCL QME approaches with exact quantum-mechanical and various semiclassical approximate kernels, we demonstrate their efficacy and accuracy in capturing the essential features of photoinduced dynamics. Our calculations show that TC QMEs generally yield more accurate results than TCL QMEs, especially in EET, although both methods offer versatile approaches adaptable across different systems. In addition, we investigate various semiclassical approximations featuring the Wigner-transformed and classical nuclear densities as well as the governing dynamics during the quantum coherence period, highlighting the trade-off between accuracy and computational cost. This work provides valuable insights into the applicability and performance of TC and TCL QME approaches via the MSH model, offering guidance for realistic applications to condensed-phase systems on the atomistic level.
A comprehensive numerical study of the effects of surface roughness on a finite-length cylinder with an aspect ratio of 1.5 for Reynolds numbers ranging from 3.9 × 103 to 4.8 × 105
Authors: Wang Zeyuan , Liu Kan , Liu Fangyuan , Wei Hongwei , Liu Qingkuan
Published: May 2024

The aerodynamic performance of the flow around a cylinder with two free ends, which is also referred to as a finite-length cylinder, continues to be a subject of rigorous academic inquiry. However, limited research has been conducted on finite-length cylinders with rough surfaces. To evaluate the impact of relative roughness on the aerodynamic performance of a finite-length cylinder, we performed numerical simulations on a cylinder model with an aspect ratio of 1.5 with various relative roughness values. These simulations covered a range of Reynolds numbers from 3.9 × 103 to 4.8 × 105. The results indicated that both the relative roughness and Reynolds number could affect the aerodynamic characteristics of the cylinder by altering the flow pattern around the cylinder. As the Reynolds number increased, the four spiral eddies behind the finite-length cylinder gradually lost their symmetry in the axial direction and eventually transformed into a pair of recirculating eddies. Moreover, when the Reynolds number was constant at 2.0 × 104, an increase in the surface roughness of the cylinder triggered the same phenomenon. Additionally, the mechanism by which the surface roughness affected the aerodynamic coefficient of a finite-length cylinder in the current Reynolds number range was revealed. This influence was mainly attributed to the impact of pressure on the backside of the cylinder.
Equilibrium configurations of line arrays with respect to the deviatoric mean drift forces
Authors: Tokić Grgur , Yue Dick K. P.
Published: May 2024

Monochromatic waves incident on an array of structures give rise to nonlinear, time-constant mean drift forces (MDFs). These forces depend on the array's spatial configuration; their magnitude and the direction is, in general, different for every structure in the array. If the spatial configuration of an array is not fixed, as is the case in arrays of individually anchor-moored structures, the time-constant differences in MDF on individual bodies can lead to a change in spatial configuration, which could, in turn, significantly affect both the first-order, time-harmonic response of the array, as well as the downwave component of the MDF. Here, we explore the dependency of these deviatoric forces on array configurations and on the frequency of the incident monochromatic waves. We consider configurations of line arrays (consisting of 2–5 vertical circular cylinders) that are described by 1 or 2 parameters, and we focus on the along-array component of deviatoric forces. Using multiple scattering computational simulations, we identify the array configurations in which the deviatoric drift forces are zero, and we discuss the stability of these equilibrium configurations with respect to class-preserving configuration perturbations. Both stable and unstable equilibria exist, but the relative number of unstable equilibria grows as the number of degrees of freedom of the configuration perturbations increases. Interestingly, the stable configurations experience a generally lower downwave mean drift force on the entire array than the unstable ones. Overall, the variations in the deviatoric and the downwave MDFs between equilibria are significant (on the order of the isolated body MDF).
Spatiotemporal dynamics of prey–predator model incorporating Holling-type II functional response with fear and its carryover effects
Authors: Dubey Balram , Singh Anand , Anshu
Published: May 2024

The recent focus in the fields of biology and ecology has centered on the significant attention given to the mathematical modeling and analyzing the spatiotemporal population distribution among species engaged in interactions. This paper explores the dynamics of the temporal and spatiotemporal delayed Bazykin-type prey–predator model, incorporating fear and its carryover effect. In our model, we incorporated a functional response of the Holling-type II. In the temporal model, a detailed dynamic analysis was carried out, investigating the positivity and boundedness of solutions, establishing the uniqueness and existence of positive interior equilibria, and examining both local and global stability. Additionally, we explored the presence of saddle-node, transcritical, and Hopf bifurcations varying attack rate parameter. The delayed system shows highly periodic behavior. Additionally, for the spatiotemporal model, we provide a complete analysis of local and global stability, and we derive the conditions for the existence of Turing instability for both self-diffusion and cross-diffusion, respectively. The two-dimensional diffusive model is further discussed, highlighting various Turing patterns, including holes, stripes, and hot and cold spots, along with their biological significance. Numerical simulations are executed to validate the analytical findings in both temporal and spatiotemporal models.
Nano-structuring of all-d-metal NiCoMnTi-based Heusler compounds
Authors: Zhang Fengqi , van Dijk Niels , Brück Ekkes , Ren Yang
Published: May 2024

The emerging all-d-metal Ni(Co)MnTi-based Heusler compounds attract extensive attention because it can potentially be employed for solid-state refrigeration. However, in comparison to the abundant physical functionalities in bulk conditions, the hidden properties related to the NiCoMnTi-based Heusler nanoparticles (NPs) have not yet been investigated experimentally. Here, we present NiCoMnTi Heusler NPs that have been manufactured by spark ablation under Ar gas flow, and the related magnetic and microstructural properties have been studied. Compared with the bulk sample, it is found that the magneto-structurally coupled transition in the bulk sample has collapsed into a magnetic transition for the NPs sample. Superparamagnetic NPs with widely distributed dislocations have directly been observed by high-resolution transmission electron microscopy. For the NPs, the magnetocrystalline anisotropy constant is 3.54 × 104 J/m3, while the saturation magnetization after post-treatment has been estimated to be around 26 Am2 kg−1. Our current research reveals that Ni-Co-Mn-Ti-based quaternary NPs could show interesting properties for future nano-application, and the produced NPs will further expand the functionalities of this material family.
Measuring friction from simulations of folded graphene sheets
Authors: Rawlins Charlie M. , Tribello Gareth A.
Published: May 2024

We ran molecular dynamics simulations of folded graphene sheets and present a procedure to measure the sliding friction in these systems based on the rate of decay of a damped harmonic oscillator. This procedure allowed us to study the effect that the size, geometry, and the temperature of the graphene sheet had on the ability to propagate the initial fold and the rate at which it settles to a final “fully folded” equilibrium state. We offer simple rationalizations for the relationships between the initial geometries of our simulations and the friction values that emerge.
In situ electric field-dependent structural changes in (Ba,Ca)(Zr,Ti)O3 with varying grain size
Authors: Kuhfuß Michel , Maier Juliana G. , Hall David A. , Xie Bingying , Kleppe Annette K. , Martin Alexander , Kakimoto Ken-ichi , Khansur Neamul H. , Webber Kyle G.
Published: May 2024

The functional properties of piezoelectric ceramic materials, such as barium titanate, are highly dependent on grain size. Lead-free polycrystalline Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) samples were prepared with a combination of the hydrothermal method and spark plasma sintering to achieve grain sizes from 100 nm to 10 μm by varying the maximum sintering temperature. In this range, a transition from a nearly linear dielectric to a ferroelectric response can be seen in macroscopic electromechanical measurements, demonstrating the importance of grain size on functional properties in BCZT. Furthermore, in situ electric field-dependent synchrotron x-ray diffraction measurements were performed to quantify the intrinsic and extrinsic strain contributions and their variations with grain size. At lower grain sizes, the data revealed a significant loss of extrinsic contributions in the piezoelectric behavior, limiting the response to intrinsic contribution associated with lattice strain. For BCZT, a critical grain size between approximately 0.08 and 0.18 μm is proposed, below which no piezoelectric response was observed.
A MASH simulation of the photoexcited dynamics of cyclobutanone
Authors: Lawrence Joseph E. , Ansari Imaad M. , Mannouch Jonathan R. , Manae Meghna A. , Asnaashari Kasra , Kelly Aaron , Richardson Jeremy O.
Published: May 2024

In response to a community prediction challenge, we simulate the nonadiabatic dynamics of cyclobutanone using the mapping approach to surface hopping (MASH). We consider the first 500 fs of relaxation following photoexcitation to the S2 state and predict the corresponding time-resolved electron-diffraction signal that will be measured by the planned experiment. 397 ab initio trajectories were obtained on the fly with state-averaged complete active space self-consistent field using a (12,11) active space. To obtain an estimate of the potential systematic error, 198 of the trajectories were calculated using an aug-cc-pVDZ basis set and 199 with a 6-31+G* basis set. MASH is a recently proposed independent trajectory method for simulating nonadiabatic dynamics, originally derived for two-state problems. As there are three relevant electronic states in this system, we used a newly developed multi-state generalization of MASH for the simulation: the uncoupled spheres multi-state MASH method (unSMASH). This study, therefore, serves both as an investigation of the photodissociation dynamics of cyclobutanone, and also as a demonstration of the applicability of unSMASH to ab initio simulations. In line with previous experimental studies, we observe that the simulated dynamics is dominated by three sets of dissociation products, C3H6 + CO, C2H4 + C2H2O, and C2H4 + CH2 + CO, and we interpret our predicted electron-diffraction signal in terms of the key features of the associated dissociation pathways.
Thin-airfoil aerodynamics in a rarefied gas wind tunnel: A theoretical study
Authors: Shapiro R. , Manela A.
Published: May 2024

We study the steady aerodynamic field and loadings about a thin flat plate placed in a wind tunnel under non-continuum conditions. Considering a two-dimensional straight tunnel configuration, the flow is driven by either density or temperature differences between the inlet and outlet tunnel reservoirs, producing a pressure gradient across the channel. Focusing on highly rarefied conditions, we derive a semi-analytic description for the gas flow field in the free-molecular limit for diffuse- and specular-wall configurations. The solution is valid at arbitrary differences between the inlet and outlet reservoirs as well as plate angles of attack α. The results are compared with direct simulation Monte Carlo calculations, indicating that the free-molecular description is valid through O(1) plate-size-based Knudsen numbers. The aerodynamic lift and drag forces are evaluated and their variations with α, reservoir conditions, and tunnel size are analyzed. At a fixed pressure ratio between the outlet and inlet reservoirs, the density-driven flow generates higher aerodynamic loads compared with its counterpart temperature-driven configuration, in line with the associated larger mass flow rate in the former. The results are discussed in light of the existing rarefied-gas description of the free-stream (non-confined) problem.
Structural, morphological, optical, electrical, and magnetic properties of aluminum-doped CoxCa(0.90−x)Ni0.10Fe2O4 flexible substrate for visible to NIR spectra applications
Authors: Billa Md. Bakey , Islam Mohammad Tariqul , Alam Touhidul , Islam Md. Shabiul , Moubark Asraf Mohamed , Alsaif Haitham , Albadran Saleh , Alzamil Ahmed , Alshammari Ahmed S.
Published: May 2024

This paper presents a conductive component tailored to a flexible substrate using Al-doped CoxCa(0.90−x)Ni0.10Fe2O4 (x = 0.25, 0.50, and 0.75) for visible to near-infrared (NIR) spectra in magneto-optical applications. The developed nanoparticles show uniformity, nanosized grains, and capillary nanopore fusion characteristics, which are confirmed by x-ray diffraction (XRD), field emission scanning electron microscopy, and energy-dispersive x-ray spectroscopy analyses, respectively. The XRD analysis revealed crystallite sizes of 33.36, 37.08, and 44.25 nm and particle sizes of 45.6, 34.6, and 31.5 nm for the compositions x = 0.25, 0.50, and 0.75, respectively. The Al-doped nanoparticles are converted to a flexible solid substrate utilizing a polyvinyl alcohol matrix, facilitating conformality to build complex shapes and broadening their application scope. The structure shows higher absorption across 450–720 nm, 480–720 nm, and 200–850 nm spectra for x = 0.25, 0.50, and 0.75, respectively. The distinctive magnetic and electrical properties are also evaluated through magnetic force microscopy and conductive atomic force microscopy, culminating in a substrate with exceptional control over light–matter interactions with smooth surfaces with lower surface roughness. The vibrating sample magnetometer analysis of the substrate shows how varying cobalt content affects magnetic properties relevant for visible to near-infrared (NIR) applications, offering insights into coercivity, magnetization, and retentivity changes at different x values. The perceptible novelties of this work are advancements in material sciences aimed at enhancing light manipulation and flexibility for electronic devices.
Jets from shocked metal surfaces with grooves: Missing experiments
Authors: Kaiser B. E. , Tregillis I. L. , Cherne F. J. , Koskelo A. C.
Published: May 2024

Many studies have investigated the mass outflows generated when a planar shock transits an imperfect (“defected”) metal surface, where the defects are symmetric triangular or sinusoidal grooves. Yet a fundamental question remains unanswered: how does the quantity of outflow mass and its maximum velocity vary as a function of the groove cross-sectional aspect ratio? We identify two sets of missing experiments that must be addressed to answer the question. The aspect ratio (groove depth over width) is equivalently represented by θ, the cross-sectional half angle, or by η0k, the amplitude multiplied by an effective wavenumber. Low θ (high η0k) grooves comprise the first set of missing experiments, which are necessary to determine the validity of theoretical predictions of the nonlinear regime (η0k≥1, θ<57.5°). The second set of missing experiments are those in which the volume of the groove (or equivalently, the axial cross-sectional area) has been held constant as θ or η0k are varied. Such experiments are necessary to independently measure the effects of variations in groove volume and groove aspect ratio on the resulting jets.
Custom-made tubular Tesla valves for laboratory lessons in classroom
Authors: Kolesov Herman N. , Dubinov Alexander E.
Published: May 2024

The article proposes new, easy-to-manufacture multivariate tubular Tesla valves that can be used in the educational process at universities and colleges. Detailed instructions for making Tesla valves from available materials using simple tools are provided. The advantages of the proposed Tesla valves over the conventional ones, described in the literature, such as manufacture ease, availability of materials and accessories, mechanical flexibility, and the ability to quickly change the number of links and change the link connection pattern, are indicated. A simple method is proposed for conducting hydrodynamic studies of liquid flow from a vessel through Tesla valves, based on measuring the water level dynamics in the vessel and, in particular, measuring the vessel's complete emptying time. Some simple experiments to demonstrate the diodicity of the valves are carried out. The repeatability and measurement errors are assessed. Parallel and series connections of valve sections are studied. The prospects for Tesla valves' use in various fields of science and technology are considered. The advantages of the proposed valves for laboratory teaching experiments in the classroom are indicated.
Photoluminescence study of anatase TiO2 photocatalysts at the pico- and nanosecond timescales
Authors: Katoh Ryuzi , Seki Kazuhiko
Published: May 2024

We studied the photoluminescence decay kinetics of three nanosized anatase TiO2 photocatalysts (particle diameter: 7, 25, or 200 nm) at the pico- and nanosecond timescales for elucidating the origin of the luminescence. Luminescence spectra from these photocatalysts obtained under steady-state excitation conditions comprised green luminescence that decayed on the picosecond timescale and red luminescence that persisted at the nanosecond timescale. Among the photocatalysts with different sizes, there were marked differences in the rate of luminescence decay at the picosecond timescale (<600 ps), although the spectral shapes were comparable. The similarity in the spectral shape indicated that self-trapped excitons (STEs) directly populated in the bulk of the particle by light excitation emit the luminescence in a picosecond timescale, and the difference in the rate of luminescence decay originated from the quenching at the particle surface. Furthermore, we theoretically considered excitation light intensity dependence on the quantum yield of the luminescence and found that the quenching reaction was not limited by the diffusion of the STEs but by the reaction at the particle surface. Both the spectral shape and time-evolution of the red luminescence from the deep trapped excitons in the nanosecond timescale varied among the photocatalysts, suggesting that the trap sites in different photocatalysts have different characteristics with respect to luminescence. Therefore, the relation between trap states and photocatalytic activity will be elucidated from the red luminescence study.
Effect of near-wall distance on velocity slip and temperature jump conditions in hypersonic rarefied gas flows
Authors: Le Nam T. P. , Dang Quang Le , Nguyen Duc-Nam , Van Dang Anh
Published: May 2024

In nonequilibrium slip and jump conditions, normal gas velocity and temperature gradients are used to calculate the gas slip velocity and temperature at the surface, respectively. Gökçen et al. (Computational fluid dynamics near the continuum limit, AIAA Paper No. 87-1115, 1987, and Gökçen and MacCormack, Nonequilibrium effects for hypersonic transitional flows using continuum approach, AIAA Paper No. 89-0461, 1989) stated that the tangential velocity and temperature of the gas molecules before a collision with the surface could be interpreted as the macroscopic tangential velocity and temperature of the gas molecules at the so-called near-wall distances auλ and aTλT away from the surface, respectively. The coefficients au and aT are the order of unity. In the present work, new forms of the slip and jump conditions are proposed by modifying the Gökçen slip and jump conditions to include the coefficients (au, aT). Numerical investigations are comprehensively conducted to determine the numerically proper values (au, aT) for the hypersonic rarefied gas flows. Cases such as the circular cylinder in cross-flow and sharp and blunted leading edge wedge are considered in the present work, with nitrogen as the working gas. The simulation results show the significant effects of the coefficients (au, aT) on the accuracy of the slip velocity and surface gas temperature predictions, and the values of au = 1.2 and aT = 1.1 show good agreement with the direct simulation Monte Carlo data.
Thermal conductivity reduction due to phonon geometrical scattering in nano-engineered epitaxial germanium
Authors: Paterson Jessy , Mitra Sunanda , Liu Yanqing , Boukhari Mustapha , Singhal Dhruv , Lacroix David , Hadji Emmanuel , Barski André , Tainoff Dimitri , Bourgeois Olivier
Published: May 2024

Nano-engineering crystalline materials can be used to tailor their thermal properties. By adding new nanoscale phonon scattering centers and controlling their size, one can effectively decrease the phonon mean free path, hence the thermal conductivity of a fully crystalline material. In this Letter, we use the 3ω method in the temperature range of 100–300 K to experimentally report on the more than threefold reduction of the thermal conductivity of an epitaxially grown crystalline germanium thin film with embedded polydispersed crystalline Ge3Mn5 nano-inclusions with diameters ranging from 5 to 25 nm. A detailed analysis of the structure of the thin film coupled with Monte Carlo simulations of phonon transport highlights the role of the nano-inclusions volume fraction in the reduction of the phononic contribution to the thermal conductivity, in particular its temperature dependence, leading to a phonon mean free path that is set by geometrical constraints.
Numerical study of wave run-up on sea dikes with vegetated foreshores
Authors: Wang Yanxu , Yin Zegao , Qiu Quanlin , Yang Guilin , Yin Dapeng
Published: May 2024

Integrating coastal vegetation into sea dikes is a nature-based approach aimed at combining disaster prevention with ecological sustainability in coastal areas. This study investigates the impact of vegetation on the wave run-up on dikes through numerical analysis. The numerical model used in the study solves the Reynolds-averaged Navier–Stokes equations by adding a vegetation resistance force to account for momentum loss. A stabilized k–ω shear stress transport model considering the vegetation effect was adopted for turbulence closure. A series of numerical simulations was carried out on the wave run-up (Ru) on dikes, focusing on the effects of different vegetation heights, densities, zone lengths, and dike slopes under various wave conditions. The results indicate that vegetation can significantly decrease Ru and may cause the wave to change from breaking to nonbreaking on dikes. The Ru behaviors depend on whether waves break and can be well characterized by the Iribarren number and dimensionless wave momentum flux parameter under breaking and nonbreaking conditions, respectively. Finally, the multivariate non-linear regression (MNLR) and artificial neural network (ANN) methods were adopted to explore a prediction model for evaluating Ru. Comparisons showed that the prediction performance of the ANN model is superior to that of the MNLR model. The ANN model has the potential as a promising predictive tool for obtaining wave run-up on dikes with vegetated foreshores under breaking and nonbreaking conditions.
Experimental realization of three types of acoustic localized states at topological interface
Authors: Ye Cheng , Chen Zhaojiang , Geng Zhi-Guo , Shen Ya-Xi , Zhu Xue-Feng
Published: May 2024

Wave localization has been the subject of extensive investigation due to its crucial importance in both applied and fundamental research. In particular, the focus has shifted to topologically protected states and flatband states. Here, we develop an acoustic topological heterostructure with one dispersive band and one flatband. In the bandgap, there is one topological state and two defect states. Drawing on this topological heterostructure, we combine three different types of wave localization and realize the flatband bound states, topological interface state, and defect states in both theory and experiment. Then, we examine how the localization of these three types of localized states varies with respect to the local coupling coefficient κBI. Our findings indicate that the topological interface state is robust in relationship to local parameter κBI, while two defect states are strongly influenced by this parameter. As for the flatband states, their eigenfrequencies are unaffected by parameter κBI, but the flatband bound state around the topological interface is dependent on this parameter. Additionally, by modifying the excitation conditions, three types of localized states can be transformed into each other. Leveraging the advantages of the localization of different types of localized states, our proposal represents a significant advancement in the potential applications of acoustic sensors and filters.
Autonomous micro-focus angle-resolved photoemission spectroscopy
Authors: Ágústsson Steinn Ýmir , Jones Alfred J. H. , Curcio Davide , Ulstrup Søren , Miwa Jill , Mottin Davide , Karras Panagiotis , Hofmann Philip
Published: May 2024

Angle-resolved photoemission spectroscopy (ARPES) is a technique used to map the occupied electronic structure of solids. Recent progress in x-ray focusing optics has led to the development of ARPES into a microscopic tool, permitting the electronic structure to be spatially mapped across the surface of a sample. This comes at the expense of a time-consuming scanning process to cover not only a three-dimensional energy-momentum (E, kx, ky) space but also the two-dimensional surface area. Here, we implement a protocol to autonomously search both k- and real-space in order to find positions of particular interest, either because of their high photoemission intensity or because of sharp spectral features. The search is based on the use of Gaussian process regression and can easily be expanded to include additional parameters or optimization criteria. This autonomous experimental control is implemented on the SGM4 micro-focus beamline of the synchrotron radiation source ASTRID2.
State-selective dissociative double ionization of CH3I and CH2I2 via I 4d core-hole states studied by multi-electron–ion coincidence spectroscopy
Authors: Fushitani Mizuho , Hikosaka Yasumasa , Tashiro Motomichi , Hishikawa Akiyoshi
Published: May 2024

The dissociative double ionization of CH3I and CH2I2 irradiated with extreme ultraviolet light at hv = 100 eV is investigated by multi-electron–ion coincidence spectroscopy using a magnetic bottle type electron spectrometer. The spin–orbit state-resolved Auger electron spectra for the I 4d core-hole states, (I 4d3/2)−1 and (I 4d5/2)−1, provide clear identifications of electronic states of CH3I2+ and CH2I22+. The dominant ion species produced after the double ionization correlate with the Auger electron energy, showing that different fragmentation pathways are open depending on the electronic states populated by the Auger decay. Theoretical calculations are performed to understand the fragmentation from the doubly charged states and the observed spin–orbit specificity in the Auger decay.