bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical properties of two-dimensional Dirac–Weyl materials with a flatband
Authors: Ye Li-Li , Han Chen-Di , Lai Ying-Cheng
Published: February 2024

The emergence of a flatband in Dirac–Weyl materials offers new possibilities for electronic transitions, leading to stronger interaction with light. As a result, the optical conductivity can be significantly enhanced in these flatband materials as compared with graphene, making them potentially better candidates for optical sensing and modulation. Recently, a comprehensive theory for the optical conductivity of a spectrum of flatband Dirac–Weyl materials has been developed, with explicit formulas for both the real and imaginary parts of the conductivity derived through two independent approaches. This Perspective offers a review of the development. An understanding of the optical properties of the flatband Dirac–Weyl materials paves the way for optical device applications in the terahertz-frequency domain.
Low-dimensional representation of intermittent geophysical turbulence with high-order statistics-informed neural networks (H-SiNN)
Authors: Foldes R. , Camporeale E. , Marino R.
Published: February 2024

We present a novel machine learning approach to reduce the dimensionality of state variables in stratified turbulent flows governed by the Navier–Stokes equations in the Boussinesq approximation. The aim of the new method is to perform an accurate reconstruction of the temperature and the three-dimensional velocity of geophysical turbulent flows developing non-homogeneities, starting from a low-dimensional representation in latent space, yet conserving important information about non-Gaussian structures captured by high-order moments of distributions. To achieve this goal, we modify the standard convolutional autoencoder (CAE) by implementing a customized loss function that enforces the accuracy of the reconstructed high-order statistical moments. We present results for compression coefficients up to 16, demonstrating how the proposed method is more efficient than a standard CAE in performing dimensionality reduction of simulations of stratified geophysical flows characterized by intermittent phenomena, as observed in the atmosphere and the oceans.
Perspective on integrated photonic devices using transparent conductive oxides: Challenges and opportunities
Authors: Wang Alan X. , Hsu Wei-Che
Published: February 2024

Transparent conductive oxides (TCOs) are gaining increasingly high research interest for integrated photonic devices due to the strong plasma dispersion effect and process compatibility with versatile optoelectronic platforms. In this perspective article, the authors gave a brief review of research efforts both on theoretical modeling and experimental demonstration of integrated photonic devices, especially on high-efficiency electro-optic modulators through the integration with plasmonics and silicon photonics. In addition, the authors discussed the challenge and opportunity associated with TCO photonic devices and the application in photonic integrated circuits (PICs) with emphasis on high mobility materials, high-speed E-O modulators, and large-scale integration. Finally, we conclude that collaboration with existing silicon photonics foundry is a necessary route to incorporate TCOs into existing PIC ecosystems.
Hybrid particle-spectral method for kinetic plasma simulations
Authors: Chapurin Oleksandr , Koshkarov Oleksandr , Delzanno Gian Luca , Roytershteyn Vadim , Brady Peter , Chiodi Robert , Harnish Cale , Livescu Daniel
Published: February 2024

A hybrid model for numerical solutions of the Vlasov–Poisson equations is presented, which blends spectral and particle approaches. The model splits the distribution function for plasma species into both spectral and particle representations in the velocity space to combine the advantages of each approach. The spectral representation leverages asymmetrically weighted Hermite basis, whereas the particle representation leverages the particle-in-cell method. Configuration phase space is decomposed with the Fourier method, which is well suited for periodic problems. We derive conservation equations for mass, momentum, and energy for the proposed combined method. It is shown that the coupling error between the two methods is absent in the semi-discrete setting (not taking into account time discretization). Finally, numerical test cases are presented simulating a weak electron beam interaction with plasma, leading to beam–plasma instability. The initially localized electron beam evolved into a highly non-equilibrium distribution function in the velocity space. A small growth rate and the resonance nature of instability make it difficult to obtain accurate solutions for purely particle methods due to noise, which falls as ∼1/Np with a number of particles. At the same time, purely spectral methods may require a large number of modes to capture the highly non-equilibrium state of the evolved beam. We show that the hybrid method is well suited for such problems: it reproduces the linear stage as well as nonlinear dynamics with sufficient accuracy using a highly non-equilibrium distribution function.
Measurement of hydrogen release of cultural heritage materials during ion beam analysis using laser-induced breakdown spectroscopy of gas enhanced by solid initiator (GENS-LIBS)
Authors: Bai Xueshi , Calligaro Thomas , Moignard Brice , Richiero Sarah , Detalle Vincent
Published: February 2024

Gas optical emission enhanced by solid initiator (GENS) is designed to support the laser-induced breakdown spectroscopy (LIBS) technique for studying the impact of intense radiation beams on cultural heritage materials. GENS-LIBS generates plasma in the atmosphere using a metal target, which increases sensitivity while lowering laser irradiance. This method is designed to monitor gas emissions from ancient materials during intense radiation analysis, particularly under ion beam irradiation. The study focused on analyzing hydrogen gas emissions from lead white pigments mixed with linseed oil as a binder in paintings. The results show that the GENS-LIBS method has allowed us to quantify the hydrogen emission of lead white-containing paint layers exposed to 10 to 40 μC/cm2 of 3 MeV protons in a specially designed sealed cell. This technique permits the tracking of hydrogen and other light elements, such as oxygen and nitrogen, thus facilitating the follow-up of changes in the material composition of artworks. GENS-LIBS offers a promising method for safely analyzing and preserving valuable cultural heritage artifacts.
Thermodynamic analysis of anomalous region, critical point, and transition from subcritical to supercritical states: Application to van der Waals and five real fluids
Authors: Wang Guo-Xiang , Almara Laura M. , Prasad Vish
Published: February 2024

All fluids exhibit large property-variations near the critical point in a region identified as the anomalous state. The anomaly starts in the liquid and extends well into the supercritical state, which can be identified thermodynamically using the Gibbs free energy (g). The specific heat, isobaric expansion, and isothermal compressibility parameters governing the transitions are: (cp/T), (vβ), and (vκ), rather cp, β, and κ. They are essentially the second-order derivatives of g and have two extrema (minimum, maximum); only maxima reported ever. When applied to the van der Waals fluid, these extrema exhibit closed loops on the phase-diagram to satisfy d3g = 0 and map the anomalous region. The predicted liquid-like to gas-like transitions are related to the ridges reported earlier, and the Widom delta falls between these loops. Evidently, in the anomalous region, both the liquid and the supercritical fluid need to be treated differently. Beyond the anomalous states, the supercritical fluids show monotonic, gradual changes in their properties. The analysis for argon, methane, nitrogen, carbon dioxide, and water validates the thermodynamic model, supports the stated observations, and identifies their delimiting pressures and temperatures for the anomalous states. It also demonstrates the applicability of the law of corresponding states. Notably, the critical point is a state where d3g = 0, the anomaly in the fluid's properties/behavior is maximal, and the governing parameters approach infinity. Also the following are presented: (a) the trajectory of the liquid–vapor line toward the melt-solid boundary and (b) a modified phase diagram (for water) exhibiting the anomalous region.
Design of the electronic structure and properties of calcium apatites via isomorphic modification of the cation sublattice, and prospects of their application
Authors: Karbivskyy V. , Kurgan N. , Hantusch M. , Romansky A. , Sukhenko I. , Karbivska L.
Published: February 2024

The evolution of the valence band, charge states of atoms, and optical and vibrational spectra in compounds Ca10−xMx(PO4)xY2, M = Fe, Ni, Cu, Mg; Y = OH, Cl, F was studied by using XPS, infrared, and optical spectroscopy, with the addition of quantum mechanics calculations. The changes in the bandgap in these compounds were analyzed. Isomorphic substitution of calcium ions in the cationic sublattice of calcium hydroxyapatite by metal ions changes the shape of the curve that represents the occupied part of the valence band only slightly. It retains a pronounced gapped character with different lengths of individual subbands—the upper and lower parts of the valence band. It is shown that the predominant position of rare earth and uranium atoms in the apatite structure is the Ca(2)-position. Isomorphic substitution of calcium atoms by metal atoms (Fe, Ni, Cu, Mg) in the apatite structure in the range of 1%–2% of atoms leads to the narrowing of the energy gap. The most significant narrowing is observed when calcium is substituted by nickel and copper. The theoretically calculated bandgap width in calcium apatites can be well described in terms of the generalized gradient approximation. The design of the structure of calcium apatites via the method of isomorphic substitutions in the cation sublattice makes it possible to control the bandgap width, thus expanding the field of practical application of these compounds.
Descriptors of water aggregation
Authors: Santis Garrett D. , Herman Kristina M. , Heindel Joseph P. , Xantheas Sotiris S.
Published: February 2024

We rely on a total of 23 (cluster size, 8 structural, and 14 connectivity) descriptors to investigate structural patterns and connectivity motifs associated with water cluster aggregation. In addition to the cluster size n (number of molecules), the 8 structural descriptors can be further categorized into (i) one-body (intramolecular): covalent OH bond length (rOH) and HOH bond angle (θHOH), (ii) two-body: OO distance (rOO), OHO angle (θOHO), and HOOX dihedral angle (ϕHOOX), where X lies on the bisector of the HOH angle, (iii) three-body: OOO angle (θOOO), and (iv) many-body: modified tetrahedral order parameter (q) to account for two-, three-, four-, five-coordinated molecules (qm, m = 2, 3, 4, 5) and radius of gyration (Rg). The 14 connectivity descriptors are all many-body in nature and consist of the AD, AAD, ADD, AADD, AAAD, AAADD adjacencies [number of hydrogen bonds accepted (A) and donated (D) by each water molecule], Wiener index, Average Shortest Path Length, hydrogen bond saturation (% HB), and number of non-short-circuited three-membered cycles, four-membered cycles, five-membered cycles, six-membered cycles, and seven-membered cycles. We mined a previously reported database of 4 948 959 water cluster minima for (H2O)n, n = 3–25 to analyze the evolution and correlation of these descriptors for the clusters within 5 kcal/mol of the putative minima. It was found that rOH and % HB correlated strongly with cluster size n, which was identified as the strongest predictor of energetic stability. Marked changes in the adjacencies and cycle count were observed, lending insight into changes in the hydrogen bond network upon aggregation. A Principal Component Analysis (PCA) was employed to identify descriptor dependencies and group clusters into specific structural patterns across different cluster sizes. The results of this study inform our understanding of how water clusters evolve in size and what appropriate descriptors of their structural and connectivity patterns are with respect to system size, stability, and similarity. The approach described in this study is general and can be easily extended to other hydrogen-bonded systems.
Pressure-dependent flow enhancement in carbon nanotubes
Authors: Li Hangtong , Ge Zhuan , Aminpour Mohammad , Wen Liaoyong , Galindo-Torres Sergio Andres
Published: February 2024

It is a known and experimentally verified fact that the flow of pressure-driven nanoconfined fluids cannot be accurately described by the Navier–Stokes (NS) equations with non-slip boundary conditions, and the measured volumetric flow rates are much higher than those predicted by macroscopical continuum models. In particular, the flow enhancement factors (the ratio between the flow rates directly measured by experiments or simulations and those predicted by the non-slip NS equation) reported by previous studies have more than five orders of magnitude differences. We showcased an anomalous phenomenon in which the flow enhancement exhibits a non-monotonic correlation with fluid pressure within the carbon nanotube with a diameter of 2 nm. Molecular dynamics simulations indicate that the inconsistency of flow behaviors is attributed to the phase transition of nanoconfined fluid induced by fluid pressures. The nanomechanical mechanisms are contributed by complex hydrogen-bonding interactions and regulated water orientations. This study suggests a method for explaining the inconsistency of flow enhancements by considering the pressure-dependent molecular structures.
Xenon tracers for cost effective laser induced fluorescence of alternative propellant Hall thrusters
Authors: Simmonds J. B. , Byrne M. P. , Chaplin V. H.
Published: February 2024

One of the limiting factors to developing plasma thrusters on alternative propellants is the cost associated with changing the diagnostic tools, which are often propellant-dependent. For laser induced fluorescence (LIF), which is typically used for ion velocity distribution measurements to determine ion trajectories and potential profiles, either new lasers need to be bought, which are tuned to the wavelength of the new element’s excitation level, or a costly tunable laser is required. A method to use existing LIF setups designed for xenon on any propellant has been demonstrated on a Hall thruster operating on krypton. In the demonstration test, a small amount of xenon (0.01%–4%) was mixed with the main krypton propellant for use as a diagnostic tracer, and xenon ion velocities were measured while also monitoring changes in the mean discharge current and oscillations. High signal-to-noise ratios in LIF data acquired along the channel centerline were obtained with tracer gas fractions ≤1% that negligibly affected the thruster operation. These results and comparison of the emission spectra of xenon and other common propellants suggest that the tracer LIF method should be broadly applicable to LIF measurements in Hall thrusters operating on alternative propellants.
Continuation criterion for solutions to the Einstein equations
Authors: Vazquez Oswaldo , Mondal Puskar
Published: February 2024

We prove a continuation condition in the context of 3 + 1 dimensional vacuum Einstein gravity in Constant Mean extrinsic Curvature (CMC) gauge. More precisely, we obtain quantitative criteria under which the physical spacetime can be extended in the future indefinitely as a solution to the Cauchy problem of the Einstein equations given regular initial data. In particular, we show that a gauge-invariant H2 Sobolev norm of the spacetime Riemann curvature remains bounded in the future time direction provided the so-called deformation tensor of the unit timelike vector field normal to the chosen CMC hypersurfaces verifies a spacetime L∞ bound. To this end, we implement a novel technique to obtain this refined estimate by using Friedlander’s parametrix for tensor wave equations on curved spacetime and Moncrief’s subsequent improvement. We conclude by providing a physical explanation of our result as well as its relation to the issues of determinism and weak cosmic censorship.
Numerical–experimental study on the stability mechanism of tail slapping motion of supercavitation projectile
Authors: Liu Rushi , Guo Zeqing , Feng Wei , Sun Shuai , Zhang Hui
Published: February 2024

Tail slapping is considered to be a prominent mode for facilitating the movement of supercavitating projectiles underwater. Stability mechanism of the tail slapping and stability criterion of projectiles was numerically investigated in this paper. A numerical method was conducted to calculate the free flight of projectiles by combining the finite volume method, the mixture multiphase model, and a dynamic meshing scheme. The accuracy and applicability of the numerical calculation method are verified by experiments. Three typical stability modes of tail slapping motion, namely, stable, conditionally stable, and unstable, were identified through the free flight numerical simulations of projectiles with varying length-to-diameter ratios under different initial angular velocities. The stability criterion of projectiles was proposed, indicating that the tail slapping stability can be determined by analyzing the curve of the moment variation with the angle of attack at any velocity above 200 m/s. Furthermore, it was found that the stable projectiles possess inherent motion states that are exclusively determined by their structural features and are unaffected by the initial motion conditions.
Experimental study on the flow mixing in T-junctions with an impeller
Authors: Yin Yuzhuo , Huang Kexin , Su Bo , Lin Mei , Wang Qiuwang
Published: February 2024

A good understanding of the mixing mechanism of hot and cold fluids in T-junctions is of great importance in ensuring the safe operation of T-junction piping systems. An impeller is added to T-junction ducts, and experiments are conducted using particle image velocimetry without considering the temperature difference between two fluids. The velocity field, vorticity field, and impeller speed are obtained for blade numbers Np = 3 and 4 at different momentum ratios (MR). When the impeller rotates passively in T-junctions under the impact of a branch jet, the values of MR required to initiate impeller rotation are MR = 0–0.5 for Np = 3 and 0–0.125 for Np = 4. However, an impeller with two blades cannot rotate at any momentum ratio. The relationship between the rotation speed and the flow rates of the main and branch fluids is obtained. An impeller with three blades rotates at a non-uniform speed, while that with four blades rotates uniformly. The jet flow pattern in T-junctions is converted from the impinging jet to the deflecting jet at MR ≥ 0.1. The average and root-mean-square velocity are essentially the same for a given momentum ratio, whereas the impeller speed increases with increasing flow rate for the main and branch ducts. As the momentum ratio decreases, the impeller speed also increases. For an impinging jet, the addition of an impeller effectively reduces the velocity fluctuation area and transfers the zone of the highest velocity fluctuation from the bottom wall to the middle of the main duct.
The influence mechanism of leakage inductance and distributed capacitance on nanosecond pulse transformer-type trigger
Authors: Lu Pengfei , Liu Hongshun , Wang Yifan , Liu Luyao , Yan Kuo , Jia Wei , Ali Abdo Ali Mohammed
Published: February 2024

The pulse trigger generator exerts a significant impact on the Marx generator’s output pulse (OP). In this paper, a pulse transformer (PT)-type trigger device is intended to give a pulse of front steepness below 30 ns, a half-width of more than 300 ns, and a magnitude of 50 kV to a 4 MV Marx generator. A steepening circuit is modeled on the output side of the PT equivalent circuit to reduce the OP front steepness, establishing the model of a closed-core PT-type trigger generator. The influence of distributed capacitance and leakage inductance (parasitic parameters) of the PT winding on the OP magnitude, triggering delay time, and front steepness are analyzed, and the design scheme of the PT is decided accordingly. Then, the pulse trigger generator model is simulated, and the trigger pulses are obtained in accordance with the design index. The OP waveforms are tested using a newly developed pulse trigger device prototype.
All-optical triangular and honeycomb lattices of exciton–polaritons
Authors: Alyatkin Sergey , Sigurðsson Helgi , Kartashov Yaroslav V. , Gnusov Ivan , Sitnik Kirill , Töpfer Julian D. , Lagoudakis Pavlos G.
Published: February 2024

We implement an all-optically reconfigurable triangular lattice of exciton–polariton condensates in a III–V semiconductor microcavity. For this, we utilize a spatial light modulator to structure an incident nonresonant excitation laser beam into a corresponding triangular lattice of Gaussian beams that are focused onto the cavity plane. The optical excitation pattern locally stimulates and blueshifts polaritons due to exciton interactions. At a critical pump power, polaritons condense into a macroscopically coherent Bloch state with sharp Bragg peaks. We reconstruct the full band structure of the system through energy tomography techniques as a function of lattice constant, allowing us to resolve polaritonic Bloch bands from the condensate emission. While for sufficiently large lattice constants, one observes the formation of triangular arrays of condensates, for small lattice constant and pump powers above condensation threshold, one observes the formation of honeycomb, instead of triangular, lattice of condensates, with clear evidence of condensation into the S-band. Our results underpin the quality of all-optically engineered polariton lattices to simulate condensed matter systems in the strong coupling regime.
Reduced dead layers and magnetic anisotropy change in La2/3Sr1/3MnO3 membranes released from an SrTiO3 substrate
Authors: Arai Takuma , Kaneta-Takada Shingo , Anh Le Duc , Kobayashi Masaki , Seki Munetoshi , Tabata Hitoshi , Tanaka Masaaki , Ohya Shinobu
Published: February 2024

We investigate the magnetic properties of La2/3Sr1/3MnO3 (LSMO) membranes released from an SrTiO3 (STO) substrate by selectively etching an Sr4Al2O7 sacrificial buffer layer. The magnetic moment and Curie temperatures (TC) of the released LSMO membranes improve significantly over their substrate-bound counterparts. We attribute these enhancements to suppressing strain and oxygen octahedral rotations that are present in substrate-bound films. Moreover, comparing the magnetic hysteresis loops obtained with magnetic fields applied along several crystallographic orientations demonstrates enhanced (weakened) perpendicular (in-plane) magnetic anisotropy in the released LSMO membranes. Our results contribute to potential applications of released LSMO membranes toward flexible spintronics devices, where high spin polarization and TC are desired.
Confinement enhanced viscosity vs shear thinning in lubricated ice friction
Authors: Baran Łukasz , MacDowell Luis G.
Published: February 2024

The ice surface is known for presenting a very small kinetic friction coefficient, but the origin of this property remains highly controversial to date. In this work, we revisit recent computer simulations of ice sliding on atomically smooth substrates, using newly calculated bulk viscosities for the TIP4P/ice water model. The results show that spontaneously formed premelting films in static conditions exhibit an effective viscosity that is about twice the bulk viscosity. However, upon approaching sliding speeds in the order of m/s, the shear rate becomes very large, and the viscosities decrease by several orders of magnitude. This shows that premelting films can act as an efficient lubrication layer despite their small thickness and illustrates an interesting interplay between confinement enhanced viscosities and shear thinning. Our results suggest that the strongly thinned viscosities that operate under the high speed skating regime could largely reduce the amount of frictional heating.
Fault mechanism and dynamic two-phase flow behavior of liquid slugging in reciprocating compressors
Authors: Li Xueying , Guo Yi , Xiong Wei , Chen Xingyu , Jia Xiaohan , Peng Xueyuan , Zhang Shengtao
Published: February 2024

Liquid slugging is a fatal fault for large process compressors, leading to transient overpressure, the deformation and fracture of vital pressure-bearing parts, and even gas leakage or explosion. In the study reported here, to reveal the mechanism of overpressure formation, numerical simulations were conducted by means of the volume-of-fluid method to explore the dynamic evolution characteristics of the two-phase flow pattern. Then, high-speed photography was applied to capture the dynamic changes of the liquid boundary in the modified cylinder from different views, thus realizing the validation of the numerical model. This study reveals the significant influence of increased rotational speed on fluid flow patterns, impeding liquid discharge and exacerbating overpressure events. Additionally, changes in pressure waveform and a distinctive waveform feature were identified as effective diagnostic indicators for detecting fluid slugging. Next, a nondestructive pressure monitoring reconstruction method based on measuring bolt strain was proposed. The strain-based pressure showed good agreement with the simulated results, thereby validating its effectiveness and feasibility as an early warning indicator for liquid slugging. This study offers new perspectives on the failure mechanism of liquid slugging in reciprocating compressors by delving into the behavior of two-phase flow, with the potential to enhance the theoretical foundation of compressor condition monitoring and fault diagnosis.
A multi-mobility model for polymer insulation: Role of high-mobility space charge on breakdown with high dv/dt voltages
Authors: Shang Xingyu , Pang Lei , Bu Qinhao , Zhang Qiaogen
Published: February 2024

The failure of polymeric solid insulation under transient voltages is closely associated with space charge. In this study, DC and AC field dependent conduction characteristics of epoxy resin were investigated using the space charge limited current and high voltage broadband dielectric spectrum methods. The breakdown voltages (BDVs) were examined over a wide range of DC voltage ramp rates. The results reveal a threshold effect of AC conduction loss below 600 Hz with respect to the electric field. By analyzing charge migration laws, a mobility distribution was deduced, with an upper limit of 10−9m2V−1s−1, which is much higher than the measured DC mobility of 10−14m2V−1s−1. A multi-mobility bipolar charge transport model was proposed by introducing the obtained mobility distribution. Compared to the single-mobility model, high-mobility carriers induce larger unblocked space charge currents for high dv/dt voltages, leading to lower values of BDV, which is consistent with experiment results. As the voltage ramp rate decreases, both simulation and experiment demonstrate higher BDVs due to the field shielding effect of homocharges.
Mechanism analysis of secondary flow and mechanical energy loss in toroidal flow field
Authors: Zhang Ke-dong , Wang Wen-hua , Yang Hao , Wang Lin-lin , Du Ya-zhen , Huang Yi
Published: February 2024

The imbalance between the radial pressure gradient and centrifugal force in curved pipe flow produces a secondary flow, resulting in a non-uniform distribution of streamwise velocity across the pipe cross section. These phenomena are believed to exhibit higher fluid resistance than straight pipes with similar flow rates, thereby motivating research into the mechanical energy losses in curved pipes. First, to ensure the accuracy and efficiency of the calculations, the results of various turbulence models were compared with direct numerical simulation to select the most appropriate turbulence model. Based on the momentum conservation equation, the mechanical influencing factors of secondary flow and streamwise velocity stratification in toroidal flow field were theoretically studied. Computational fluid dynamics method was employed to explore the spatiotemporal evolution characteristics of the mechanics and velocity distribution in transient flow fields to explain the formation mechanism of the secondary flow and the coupling relationship between the streamwise and radial directions. Then, the typical energy components of the toroidal flow field were analyzed using the energy equation, and the energy conservation and distribution characteristics were numerically studied. Furthermore, the influence of typical parameters (Reynolds number and curvature ratio) on the velocity distributions and mechanical properties as well as the percentage and distribution of various energy components were analyzed. Finally, the calculation results were statistically presented to quantify the variation of the energy components with typical parameters.
Numerical study of the Marangoni effect induced by soluble surfactants and solute based on rising droplets
Authors: Mao Qi , Yang Qing-Jun , Li Yu-Long , Cao Wang
Published: February 2024

In this study, we present a numerical investigation into the phenomenon of rising droplets in immiscible fluids, focusing on the Marangoni effect induced by both solute and a combination of solute and soluble surfactants. We meticulously examine the interfacial behaviors of pure solute droplets and mixed droplets, with a particular interest on the intricate interplay among interfacial concentration, interfacial tension, Marangoni stress, and Marangoni convection. Our investigation provides insight into the influence of key physicochemical parameters, such as viscosity, diffusion coefficient, partition coefficient, and interfacial tension gradient, on the Marangoni instability. Furthermore, we conduct a comprehensive parametric exploration of the impact of dimensionless numbers such as the Langmuir number (La), the Damkohler number (Da), the Peclet number (Pe), and the elasticity number β on the stabilizing efficacy of surfactants. The research findings underscore the effectiveness of our numerical method in capturing the distinctive two-step acceleration characteristics of pure solute droplets and the stabilizing effect of surfactants on mixed droplets. Notably, our study reveals that the Marangoni instability may manifest even when the viscosity and diffusivity ratios of the two-phase fluids are closely matched. Partition coefficients below unity exhibit only a marginal influence on the re-acceleration time of the droplets. Systems characterized by extremely low interfacial tension gradients tend to exhibit no Marangoni instability. Moreover, an increase in La enhances the stability of mixed droplets, while a significant threshold is identified for Da to affect the stability of mixed droplets. The ascent speed of mixed droplets displays pronounced variation across varying Pe magnitudes. Finally, in scenarios involving a wide-ranging variation in β, mixed droplets transition between the states of pure solute droplets and rigid spheres, revealing a distinct-state transition point.
Experimental demonstration of intracavity multiaxial geometric mode structure manipulation
Authors: An Jiashuo , Bai Zhenxu , Zhu Zhihan , Wang Yulei , Lu Zhiwei
Published: February 2024

Coherent wave multiaxial geometric modes (MAGMs) are a type of complex structured light characterized by ray-wave duality. Multiple spatial degrees-of-freedom of MAGMs are attractive for some advanced areas such as high-capacity optical communications. Conventionally, transverse light field coupled to ray-trajectories of geometric mode from lasers is hard to be tailored. Here, intracavity manipulation of the transverse structure of MAGMs is experimentally demonstrated. A spot-defect was employed to realize loss control and couple various structured transverse modes including Hermite–Gaussian modes and Laguerre–Gaussian modes to rays of MAGMs. More interestingly, we experimentally demonstrate that sub-MAGMs can also be coupled to ray-trajectories of MAGMs, and multi-ray geometric modes twisted light can be obtained. This work reveals that the dimension of light field can be further expanded and open perspectives on high-dimensional structured light physics and applications.
Long-term day-by-day tracking of microvascular networks sprouting in fibrin gels: From detailed morphological analyses to general growth rules
Authors: Rojek Katarzyna O. , Wrzos Antoni , Żukowski Stanisław , Bogdan Michał , Lisicki Maciej , Szymczak Piotr , Guzowski Jan
Published: February 2024

Understanding and controlling of the evolution of sprouting vascular networks remains one of the basic challenges in tissue engineering. Previous studies on the vascularization dynamics have typically focused only on the phase of intense growth and often lacked spatial control over the initial cell arrangement. Here, we perform long-term day-by-day analysis of tens of isolated microvasculatures sprouting from endothelial cell-coated spherical beads embedded in an external fibrin gel. We systematically study the topological evolution of the sprouting networks over their whole lifespan, i.e., for at least 14 days. We develop a custom image analysis toolkit and quantify (i) the overall length and area of the sprouts, (ii) the distributions of segment lengths and branching angles, and (iii) the average number of branch generations—a measure of network complexity. We show that higher concentrations of vascular endothelial growth factor (VEGF) lead to earlier sprouting and more branched networks, yet without significantly affecting the speed of growth of individual sprouts. We find that the mean branching angle is weakly dependent on VEGF and typically in the range of 60°–75°, suggesting that, by comparison with the available diffusion-limited growth models, the bifurcating tips tend to follow local VEGF gradients. At high VEGF concentrations, we observe exponential distributions of segment lengths, which signify purely stochastic branching. Our results—due to their high statistical relevance—may serve as a benchmark for predictive models, while our new image analysis toolkit, offering unique features and high speed of operation, could be exploited in future angiogenic drug tests.
Droplet impacting dynamics on a thin liquid film on the rice-leaf microstructured surface
Authors: An Yongze , Hao Yiyao , Wang Chaoxi , Xue Jinlin , Qiu Wei , Chen Yunfu
Published: February 2024

Although spraying pesticides onto stems and leaves is the most effective method to prevent plant pests and diseases, the splashing of the droplets upon impact with the leaf surface is one of the main ways that the liquid agent is lost during the application process. Moreover, the collision and impact of flowing droplets with the liquid film are complex owing to the presence of microstructures on the leaf surface. Therefore, understanding the droplet impact dynamics is crucial for improving the pesticide application process. In this paper, a simulated rice leaf with a microstructured surface was established, and the impacting dynamics of a liquid droplet on this surface with thin liquid film were investigated using numerical methods. Specifically, the influences of different droplet diameters, droplet velocities, liquid film thicknesses, and leaf surface microstructure dimensions on the impacting dynamics were analyzed. The results showed that the behavior of spreading, jetting, rebound, and splashing occurred upon when droplets impact the simulated surface of rice leaves with thin liquid film. Moreover, a larger droplet diameter and a higher velocity lead to an increase in both the maximum height and diameter of the formed crown. Additionally, the thicker liquid films result in crowns with a smaller base radius. When the jetting angle increases, the crown height increases while its base radius decreases. With the increase in the rib spacing of microstructure, the maximum crown height initially increases and then decreases, while the crown base radius decreases. However, the rib depth has no significant influence on the base radius of the crown. Equations for the quantitative expression of the transition relationships between the deposition, jetting, and splashing phenomena were established on the basis of the Reynolds number, Ohnesorge number, and Weber number as well as the dimensionless liquid film thickness.
A molecular density functional theory for associating fluids in 3D geometries
Authors: Barthes Antoine , Bernet Thomas , Grégoire David , Miqueu Christelle
Published: February 2024

A new free-energy functional is proposed for inhomogeneous associating fluids. The general formulation of Wertheim’s thermodynamic perturbation theory is considered as the starting point of the derivation. We apply the hypotheses of the statistical associating fluid theory in the classical density functional theory (DFT) framework to obtain a tractable expression of the free-energy functional for inhomogeneous associating fluids. Specific weighted functions are introduced in our framework to describe association interactions for a fluid under confinement. These weighted functions have a mathematical structure similar to the weighted densities of the fundamental-measure theory (i.e., they can be expressed as convolution products) such that they can be efficiently evaluated with Fourier transforms in a 3D space. The resulting free-energy functional can be employed to determine the microscopic structure of inhomogeneous associating fluids of arbitrary 3D geometry. The new model is first compared with Monte Carlo simulations and previous versions of DFT for a planar hard wall system in order to check its consistency in a 1D case. As an example of application in a 3D configuration, we then investigate the extreme confinement of an associating hard-sphere fluid inside an anisotropic open cavity with a shape that mimics a simplified model of zeolite. Both the density distribution and the corresponding molecular bonding profile are given, revealing complementary information to understand the structure of the associating fluid inside the cavity network. The impact of the degree of association on the preferential positions of the molecules inside the cavity is investigated as well as the competition between association and steric effect on adsorption.
Near room-temperature ferromagnetism in BixCr1−xTe2 epitaxial thin films grown on GaAs(111)B by molecular beam epitaxy
Authors: Yan Pengfei , Xu Yongkang , Wang Jin , Zhang Xiaolong , Dai Xingze , Wang Chao , He Liang
Published: February 2024

Two-dimensional (2D) ferromagnetic materials (FMs) are potentially the material foundation for future spintronics devices. However, at present, the Curie temperature (TC) of most 2D FM is relatively low and cannot meet the need for practical applications. Nowadays, CrTe2 thin films grown by molecular beam epitaxy (MBE) are reported to be room-temperature ferromagnetic only on graphene substrate instead of 3D substrates. In this work, we report high-quality Bi-doped CrTe2 (BixCr1−xTe2) thin films grown on conventional substrates of GaAs(111)B by MBE. Magnetotransport measurements reveal strong ferromagnetism of all the films, with out-of-plane magnetic anisotropy. More importantly, as more Bi atoms are doped into the film, the Curie temperature increases and reaches 305 K at x = 0.1. This improvement is a step forward for its application in spintronics and other fields.
Experimental evidence of enhanced radial transport in small ELM regimes at DIII-D
Authors: Perillo R. , Boedo J. A. , Lasnier C. J. , McLean A. , Bykov I. , Marini C. , Rudakov D. L. , Watkins J. G. ,   DIII-D Team
Published: February 2024

Small/type-II edge-localized-modes (ELMs), carrying 1% of the plasma stored energy, are found to deposit only 45 ± 5% of the ELM power near the strike point, and the remaining 55 ± 5% to the far scrape-off-layer (SOL). Small ELMs spread their power over a larger area compared to type-I ELMs, where such a ratio is about 60% and 40% for near- and far-SOL regions, respectively. The larger spread is reflected in the heat flux width (λq) in the SOL for the intra-small ELMs profile of 6.0 mm, almost a factor 2 larger than that of type-I ELMs of 3.15 mm, for similar plasma conditions and magnetic configuration. At the ELM peak, the small ELMs λq is found to be up to 4 times larger than for the type-I ELMs, going from 2 to 7.9 mm, indicating enhanced radial transport in the neon-seeded small ELM scenario. Inter-ELM λqs have been also calculated at the secondary outer divertor in quasi-double-null (QDN) discharges. It is found that, on average, λq is 2.2 times larger in the high-separatrix-density small ELM regime, compared to a reference type-I ELM one. These findings are supported by small ELMs radial velocity profiles, measured at the outer midplane with a fast reciprocating probe, showing a decay length (λvr) in the SOL of 12.8 cm, which is 3.3 times larger than that for the type-I ELMs of 3.9 cm. This analysis shows that small ELMs, although attractive for future machines due to low peak heat flux and large λq, might be of concern for the larger flux to the outer wall.
Comparing first-principles density functionals plus corrections for the lattice dynamics of YBa2Cu3O6
Authors: Ning Jinliang , Lane Christopher , Barbiellini Bernardo , Markiewicz Robert S. , Bansil Arun , Ruzsinszky Adrienn , Perdew John P. , Sun Jianwei
Published: February 2024

The enigmatic mechanism underlying unconventional high-temperature superconductivity, especially the role of lattice dynamics, has remained a subject of debate. Theoretical insights have long been hindered due to the lack of an accurate first-principles description of the lattice dynamics of cuprates. Recently, using the r2SCAN meta-generalized gradient approximation (meta-GGA) functional, we have been able to achieve accurate phonon spectra of an insulating cuprate YBa2Cu3O6 and discover significant magnetoelastic coupling in experimentally interesting Cu–O bond stretching optical modes [Ning et al., Phys. Rev. B 107, 045126 (2023)]. We extend this work by comparing Perdew–Burke–Ernzerhof and r2SCAN performances with corrections from the on-site Hubbard U and the D4 van der Waals (vdW) methods, aiming at further understanding on both the materials science side and the density functional side. We demonstrate the importance of vdW and self-interaction corrections for accurate first-principles YBa2Cu3O6 lattice dynamics. Since r2SCAN by itself partially accounts for these effects, the good performance of r2SCAN is now more fully explained. In addition, the performances of the Tao–Mo series of meta-GGAs, which are constructed in a different way from the strongly constrained and appropriately normed (SCAN) meta-GGA and its revised version r2SCAN, are also compared and discussed.
Development of a gas jet coupled electron cyclotron resonance ion source for radioactive ion beam
Authors: Bhattacharjee Mahuwa , Giri Chinmay , Masum Syed , Hansda Sunita , Mitra Sulagna , Haque Sanket , Chakraborty Pratanu , Dechoudhury Siddhartha , Ray Ayan , Mondal Manas , Nayan Balram Kumar , Shukla Vinay , Sanyal Dirtha , Bandyopadhyay Arup , Naik Vaishali
Published: February 2024

A 2.45 GHz electron cyclotron resonance (ECR) ion source coupled to a gas-jet skimmer system has been developed for the online production of radioactive ion beams (RIBs). Using radial injection of gas jet in the ion source, RIBs of 11C1+, 11CO21+, and 11CO1+ have been produced online with beam intensity up to about 9 × 103 particles per second for a 1 µA primary proton beam bombarding a nitrogen gas target. The details of the gas jet coupled ECR ion source and the results for stable isotope beams and RIBs are reported.
Theoretical basis for interpreting heterodyne chirality-selective sum frequency generation spectra of water
Authors: Konstantinovsky Daniel , Santiago Ty , Tremblay Matthew , Simpson Garth J. , Hammes-Schiffer Sharon , Yan Elsa C. Y.
Published: February 2024

Chirality-selective vibrational sum frequency generation (chiral SFG) spectroscopy has emerged as a powerful technique for the study of biomolecular hydration water due to its sensitivity to the induced chirality of the first hydration shell. Thus far, water O–H vibrational bands in phase-resolved heterodyne chiral SFG spectra have been fit using one Lorentzian function per vibrational band, and the resulting fit has been used to infer the underlying frequency distribution. Here, we show that this approach may not correctly reveal the structure and dynamics of hydration water. Our analysis illustrates that the chiral SFG responses of symmetric and asymmetric O–H stretch modes of water have opposite phase and equal magnitude and are separated in energy by intramolecular vibrational coupling and a heterogeneous environment. The sum of the symmetric and asymmetric responses implies that an O–H stretch in a heterodyne chiral SFG spectrum should appear as two peaks with opposite phase and equal amplitude. Using pairs of Lorentzian functions to fit water O–H stretch vibrational bands, we improve spectral fitting of previously acquired experimental spectra of model β-sheet proteins and reduce the number of free parameters. The fitting allows us to estimate the vibrational frequency distribution and thus reveals the molecular interactions of water in hydration shells of biomolecules directly from chiral SFG spectra.
Optimizing electron injection barriers and hole-trapping ability for high-performance photomultiplication-type ternary organic photodetectors
Authors: Huang Jiang , Fan Qingshan , Jin Ziheng , Zhang Hanqing , Dou Zifan , Wang Meiling , Li Jian , Xu Lin , Zhou Guanrui , Zhang Ting , Chen Shi
Published: February 2024

Photomultiplication-type organic photodetectors (PM-OPDs) have been stimulating more and more researchers' interest owing to their extremely high external quantum efficiency (EQE). To prepare high-performance PM-OPDs with a broadband spectral response range from visible to near-infrared and investigate the role of energy levels of the donor and acceptor on its responsiveness, the non-fullerene acceptor Y6 was added into the P3HT:PC71BM system in this work. The photomultiplication phenomenon with the highest EQE has been achieved under both forward and reverse bias when the ratio of Y6 in two acceptors approaches 80 wt. %. The introduction of Y6 not only promotes the formation of moderate hole traps in the active layer but also results in an appropriate amount of low injection barriers to allow more electron injection from the external circuit. Therefore, the spectral response of the device with 80 wt. % Y6 has been broadened from 750 to 950 nm, and the champion EQE of 15 691% at 10 V and 7639% at −20 V at 850 nm was achieved. This work reveals the importance of hole-trapping ability determined by the energy level difference between the donor and the acceptor for the selection of the multiplication system and provides a scheme for the design of high-performance broadband PM-OPDs.