bluuebunny/crossref_metadata_2025 huggingface dataset:
Point-contact spectroscopy of heterocontacts in superconducting and normal states
Authors: Tulina N. A. , Kuzemchenko M. A.
Published: January 2025

The point-contact spectra of rhenium–zinc and rhenium–copper heterocontacts were studied (the rhenium contact was in both a normal and superconducting state). It is shown that both metals contribute to the point-contact spectrum of a heterocontact, and in addition the magnitude of the partial contributions is inversely proportional to the Fermi velocities, confirming the results of the theory of the point-contact spectroscopy of heterocontacts. The possibility of point-contact spectroscopy in the superconducting state is demonstrated.
Flicker noise and electron–phonon interaction in metallic point contacts
Authors: Zagoskin A. M. , Kulik I. O. , Omel’yanchuk A. N.
Published: January 2025

Flicker noise in metallic point contacts, due to the scattering of electrons by two-level systems (TLS), was studied. In the diffusion regime le−im ≪ d the intensity of the noise obeys the 1/Ne law, while in the ballistic limit le−im ≫ d it obeys the 1/Ne1/3 law (Ne is the number of charge carriers in the region with a volume of V0 ∼ d3, le−im is the electron-impurity scattering length). When electron–phonon scattering is taken into account the bias-voltage dependence of the spectral intensity of the noise has certain features (of the smoothed step type) with a relative intensity of the order of d/le−ph for biases equal to the characteristic phonon energies. These features are most distinct when the number of TLS in the contact is small, when the important TLS are those which lie at distances from the contact of the order of or greater than the electron–phonon relaxation length le−ph.
Point-contact electron–phonon interaction function in tantalum
Authors: Bobrov N. L. , Rybal’chenko L. F. , Fisun V. V. , Yanson I. K.
Published: January 2025

Tantalum is studied by the method of point-contact (PC) spectroscopy: the parameter λpc and the absolute intensity of the PC EPI function are determined, and the form of the EPI function is determined more accurately. Both homocontacts Ta–Ta and heterocontacts Ta–Cu and Ta-Au were studied. It was found that the contributions of copper and gold to the spectrum of the heterocontact are not noticeable, though the forms of the PC spectra of Ta in homo- and heterocontacts are different. The intensities of the spectra of Ta–Ta homocontacts and Ta–Cu heterocontacts turned out to be close to one another. Simple expressions, enabling numerical calculations of the PC characteristics for geometrically symmetric heterocontacts in the approximation of a spherical Fermi surface, are derived, based on the theory. It is shown that the use of the free-electron approximation in the numerical estimates leads to an error. It is proposed that the effective mass approximation be used for such estimates.
Nonlinear excitations under low-temperature excitation of high-amplitude vibrations in crystals containing dislocations
Authors: Pal’-Val’ P. P. , Kaufmann H. -J.
Published: January 2025

The resonance characteristics of silicon single crystals have been investigated at 5.9° K near the frequency of the main resonance of a quartz-sample system. The asymmetry and hysteresis of the resonance peak, which were observed in the region of high-amplitude vibrations and were accompanied by a substantial decrease in the resonance frequency and an abrupt change in the amplitude of the vibrations, are attributed to the nonlinear nature of the dislocation motion in the internal-stress fields of the crystal.
Thermoelectric processes in superconductors and their contribution to the thermo-emf of SNS systems
Authors: Logvenov G. Yu. , Ryazanov V. V.
Published: January 2025

Thermoelectric phenomena in Josephson SNS Ta–Cu–Ta sandwiches were studied experimentally in the temperature range from 0.8Tc up to the critical temperature Tc of superconducting tantalum. The quantitative characteristics of the thermoelectric analog of the Josephson effect and the peculiarities of its use for studying thermoelectric processes in superconductors were studied. An equivalent circuit is proposed for an SNS junction in the case when heat flows through the junction, which describes the nonequilibrium processes appearing at the NS boundaries. The effect of Andreev reflection on the thermoelectric characteristics of Josephson SNS systems is taken into account.
Superconductivity and thermal anomalies in the properties of the crystal lattice of the metal oxide La1.8Ba0.2CuO4−y
Authors: Gabovich A. M. , Medvedev V. A. , Moiseev D. P. , Motuz A. A. , Prikhot’ko A. F. , Prokopovich L. V. , Solodukhin A. V. , Khirunenko L. I. , Shinkarenko V. K. , Shpigel’ A. S. , Yachmenev V. E.
Published: January 2025

We have measured in the superconductor La1.8Ba0.2CuO4−y, the temperature dependence of the specific heat Cp, the infrared absorption spectrum, and the linear expansion coefficient α. Near the superconducting transition temperature Tc, which was determined by resistance measurements, we observed jumps in the specific heat ΔC and anomalies in α, suggesting that the superconductivity is a bulk effect. We have computed the T dependence of the upper critical field Hc2 when T ≲ Tc in a superconductor with a dielectric gap Σ on parts of the Fermi surface. We show that Hc2(T) can be quite different from the case where Σ = 0, in agreement with experiment.
The role of optical phonons in high-temperature superconductivity
Authors: Verkin B. I. , Dmitriev V. M.
Published: January 2025

We have studied the absorption spectra of the high-temperature superconductors Y(La)Ba(Sr)CuO in the frequency range from 400 to 3600 cm−1 and compared their superconducting properties. In the lanthanum compounds the superconducting mechanism is closely tied to phonons whose energies are approximately 64 meV. In yttrium compounds 140 meV optical phonons are important.
Variable valence and correlation pairing of carriers in Fermi systems with repulsion
Authors: Ukrainskiĭ I. I.
Published: January 2025

Topological pairing of current-confinement carriers is shown to be possible in the two-dimensional lattice Fermi gas with repulsion. This causes a BCS-type state to arise in the absence of phonons. When the theory developed is applied to systems of the LaBaCuO type, an estimate of the order of 200 °K is obtained for the pairing-destruction temperature.
Critical parameters and nonlinear dissipative properties of superconducting films in a strong high-frequency field
Authors: Bezuglyi E. V. , Dmitriev V. M. , Svetlov V. N. , Churilov G. E. , Azovskii A. Yu.
Published: January 2025

We studied, both theoretically and experimentally, the dependence of the critical current in a superconducting film on the frequency and power of electromagnetic waves in the frequency range from 15 MHz to 104 MHz. The good agreement between the theoretical and experimental results enables us to determine the microscopic relaxation times of the order parameter τΔ and the quasiparticle distribution τϵ in the nonlinear regime where the amplitude of the variable current is comparable to the critical current. We find that the observed transition of the superconducting film into the resistive state is due to the dynamical Ginzburg–Landau depairing mechanism and not to either thermal or kinetic effects. We compute the nonlinear high-frequency dissipative conductivity of a superconducting film that has an anomaly in the neighborhood of the superconductor’s relaxation frequencies.
Avalanche (explosive) crystallization of amorphous vanadium and antimony films
Authors: Kuz’menko V. M. , Mel’nikov V. I. , Vladychkin A. N. , Rakhubovskiĭ V. A. , Sudovtsov A. I.
Published: January 2025

The process of avalanche crystallization of vanadium and antimony amorphous films, condensed on liquid-helium-cooled substrates, is studied. We also determine the velocity of the avalanche-crystallization front and the activation energy of the transition. The results are found to be in qualitative agreement with the modem theory.
Quantum oscillations of the contact potential difference
Authors: Semenchinskiĭ S. G. , Édel’man V. S.
Published: January 2025

It is shown that, because of screening, quantum oscillations, owing to the oscillations of the chemical potential in the bulk of the metal, in the contact potential difference in a magnetic field are determined by the factor ∼ exp(− D/H/rs) (DH is the diameter of the electron orbit in a magnetic field and rs is the screening radius).
High sensitivity of the superconducting transition temperature of heterophase titanium alloys to the rate of cooling
Authors: Eremin V. I. , Moskalenko V. A.
Published: January 2025

A strong influence of the cooling rate, T˙, of specimens on the transition temperature Tc and its kinetics has been found in measuring the superconducting transition in two-phase (α + β) titanium alloys of the Ti–Al–V system. Under standard (slow) cooling conditions, Tc in these alloys varies between 5.7 and 7.0 °K depending on the vanadium concentration. The maximum effect was obtained for T˙ about 10 °K-sec−1, when an unstable and irreversible N–S transition was recorded with Tc = 36 °K and a start of the transition at 42 °K. It is proposed that so great a shift in Tc towards higher temperatures for fairly rapid cooling of the specimen is a consequence of thermoelastic strains arising in it, initiating lattice instability in the vicinity of the structural phase transition in the superconducting β phase.
Josephson effects in Y1Ba2Cu3O7−x point contacts
Authors: Verkin B. I. , Bondarenko S. I. , Dmitriev V. M. , Lukashenko A. V. , Seminozhenko V. P. , Shablo A. A.
Published: January 2025

The Josephson properties of pressure point contacts of Y1Ba2Cu3O7−x ceramics are investigated experimentally. It is shown that the Josephson properties of such contacts are preserved up to Tc of the contacts, which is close to liquid nitrogen temperatures for some samples investigated. Examination of the temperature dependence of the critical and excess currents permits a conclusion about the similarity of ceramic–ceramic pressure point contacts with S–N–S junctions.
Reflection of second sound at a bcc 4He–He II interface
Authors: Dyumin N. E. , Grigor’ev V. N. , Svatko S. V.
Published: January 2025

The reflection coefficient for second sound at a bcc 4He–He II interface has been measured. It is shown that such an interface has high mobility and the calculated value of the crystal growth coefficient is given by a temperature dependence close to eΔp/T.
Autocorrelation functions of an isotropic paramagnetic Fermi liquid at Landau attenuation threshold
Authors: Kaganov M. I. , Czerwonko J.
Published: January 2025

The calculation of the autocorrelation functions of density (spin density) and transverse current (spin current) for a degenerate Fermi liquid is reduced to the algebraic problem of inversion of a particular matrix. This approach is used to obtain the autocorrelation function asymptotics at the Landau attenuation threshold, i.e., for ω/kv ≡ μ → l, where ω and k are the frequency and wave vector of the external field, and v is the Fermi velocity. It is proved that the autocorrelation functions of density (spin density) and transverse current (spin current) are linear fractional functions of the variables q = ln[(l − μ/2 + i0] and (1 − μ)q under the assumption that terms of the order of (1 − μ)q and (1 − μ) are neglected in comparison to q and (1 − μ)q, respectively. The particular shape of the asymptotics is calculated for three nonzero Landau parameters. The formulas obtained may be used for studying the nonexponential decay (from the sample boundary) of fields in 3He and alkali metals.
Excitation of nonlinear magnetic waves
Authors: Lyubchanskii I. L. , Sobolev V. L. , Soboleva T. K.
Published: January 2025

The relation between the external force and crystal parameters during the excitation of nonlinear magnetization waves is determined. The excitation of solitons by an external, spatially nonuniform magnetic field in easy-plane ferromagnets and by light in rare-earth orthoferrite is considered. Corresponding experimental techniques are proposed.
Rotational diffusion of H2μ+ ions in crystalline hydrogen
Authors: Storchak V. G.
Published: January 2025

The model of below-barrier rotations of H2μ+ ions makes it possible to explain the experimentally observed (Barsov et al.1) temperature dependence of the muon depolarization rate in parahydrogen. An experiment to test the model is suggested.
Measurements of the diamagnetic moment of yttrium-based metal-oxide ceramic
Authors: Grigut’ O. V. , Ivanchenko Yu. M. , Malyshev E. N. , Mikheenko P. N. , Revenko Yu. F.
Published: January 2025

Inductive measurements of the temperature dependence of the diamagnetic moment of the metal oxide ceramic Y1.2Ba0.8CuO4 were performed. The diamagnetic properties of this ceramic were compared with the resistive properties. Their evolution was followed. The percentage content of the superconducting phase was determined. It is concluded that the conductivity has a percolation character and the links between the ceramic granules are Josephson links. It was discovered that a surface superconducting interlayer is formed, and its thickness is determined. The contribution of the paramagnetic phase present in the ceramic to the inductance is discussed.
Experimental observation of the vibration-rotation effect in He II
Authors: Kolesnik V. I. , Mikheev V. A. , Rybalko A. S. , Sokolov S. S.
Published: January 2025

The results of the experimental observation of the vibration-rotation effect in liquid He, predicted by Gurevich, Sonin, and Fomin, are presented. Rotation of the liquid was observed in both the normal and superconducting phases. The behavior of the angular rotational velocity as a function of the temperature was studied in the temperature interval 2.3–1.4 K. The experimental dependences Ω(T) obtained are described satisfactorily by a square root dependence on the viscosity. Analysis of the available data gives a basis for assuming that the superfluid component of He participates in the rotation.
Crystallographic anisotropy of the reflection of conduction electrons from a sample surface in bismuth
Authors: Bozhko S. I. , Tsoĭ V. S.
Published: January 2025

The crystallographic anisotropy of the probability of specular reflection q of conduction electrons from a sample surface in Bi and the effect of chemical and ion etching of the trigonal plane on the character of the electron reflection were studied experimentally with the help of electron focusing with a transverse magnetic field. It was found that q is large (≈ 0.8) for surfaces close to the trigonal plane. Inclination of the sample surface from the trigonal plane by an angle greater than 20° and etching of the surface of the samples suppressed the specularity (q ≈ 0. 1 − 0.2). The results are discussed from the viewpoint of electron scattering by a rough surface and by adsorbed, randomly distributed, charged impurities.
Peculiarities of ferrous fluosilicate magnetization at low temperatures in randomly oriented magnetic fields
Authors: Asadov S. K. , Zavadskii É. A. , Zavorotnev Yu. D. , Todris B. M.
Published: January 2025

The energy spectrum of the Fe2+ ion in ferrous fluosilicate is reconstructed on the basis of measurements in a strong pulsed magnetic field of random orientation. The temperature variation of a single crystal under investigation is studied for the process of adiabatic magnetization.
Anisotropy of Zeeman splitting for conduction electrons in palladium and gold
Authors: Grechnev G. E. , Savchenko N. V. , Svechkarev I. V. , Antonov V. N. , Zhalko-Titarenko A. V. , Li M. J. G. , Perts J. M.
Published: January 2025

The g factors of conduction electrons in palladium and gold are studied theoretically. It is established that for a number of sheets of the Fermi surface of these metals the g factor differs significantly from the free-electron value and exhibits a strong angular dependence for extremal orbits in palladium on the Δ6 sheet and X ellipsoids. The results obtained agree with the data on the de Haas–van Alphen effect and electron paramagnetic resonance.
Dielectric-constant anomalies of liquid ortho/para hydrogen mixtures
Authors: Pashkov V. V. , Marinin V. S.
Published: January 2025

The dielectric properties of liquid ortho/para hydrogen mixtures are considered in terms of the Onsager–Böttcher model, generalized to the case of an ellipsoidal cavity with allowance for the quantum contributions to the polarization. The excess dielectric constant δε (relative to pure p-H2), found as a function of the temperature and the composition, is in good agreement with the experimental data. An analysis is made into the causes of the observed anomalies in the behavior of δε (T, x).
Spectroscopy of phonons in tin and indium superconducting point-contacts
Authors: Kamarchuk G. V. , Khotkevich A. V.
Published: January 2025

Tin and indium point-contacts in the normal and superconducting states were studied. The second derivatives of the current–voltage characteristics and of the voltage dependence of the excess current in the point-contact were measured. The measurements were performed for different fixed values of the temperature and magnetic field intensity. Features due to the electron–phonon interaction were observed in the spectra of clean contacts in the superconducting state. It is shown that as the parity of the metal decreases it becomes more difficult to resolve the features produced by the electron–phonon interaction in the second derivatives of the current–voltage characteristics of superconducting contacts.
Sign-alternating temperature dependence of the thermo-emf of pure silver
Authors: Il’evskiĭ V. I. , Kopeliovich A. I. , Morgun V. N.
Published: January 2025

An explanation is proposed for the sign-alternating temperature dependence of the thermo-emf of pure silver, based on a systematic analysis of small-angle electron–phonon scattering taking into account entrainment and U processes.
Transient transfer processes for large heat pulses from a film heater to superfluid helium
Authors: Danil’chenko B. A. , Lutset M. O. , Poroshin V. N.
Published: January 2025

Measurements that characterize the boiling of superfluid helium are described, from which conclusions are drawn about the formation of a helium layer which, for the transfer of large heat pulses, is strongly out of equilibrium with respect to the normal component adjacent to the heater.
Dynamic scheme for the description of two-band superconductors. Collective modes
Authors: Galaiko V. P. , Shumeiko V. S.
Published: January 2025

Dynamic equation for the density matrix of a two-band superconductor are constructed. For the case of a narrow band, the collective oscillations are analyzed and a weakly damped mode is found which, being the characteristic property of such superconductors, can be used in their experimental identification.
Current algebras from QP-manifolds in general dimensions
Authors: Ikeda Noriaki , Xu Xiaomeng
Published: January 2025

We propose a new unified formulation of the current algebra theory in general dimensions in terms of supergeometry. We take a QP-manifold, i.e., a differential graded symplectic manifold, as a fundamental framework. A Poisson bracket in a current algebra is constructed by the so called derived bracket of the graded Poisson structure induced from the above QP-structure. By taking a canonical transformation on a QP-manifold, correct anomalous terms in physical theories are derived. A large class of current algebras with and without anomalous terms (central extensions) are constructed from the above structure. Moreover, using this formulation, a new class of current algebras related higher structures are systematically obtained.
Study of carrier diffusion in InGaN/GaN quantum wells: Impact of quantum well thickness and substrate type
Authors: Litschgi Simon , Dussaigne Amélie , Barbier Frédéric , Veux Guillaume , Cibié Anthony , Gayral Bruno , Rol Fabian
Published: January 2025

In InGaN/GaN micro-light-emitting diodes (μLEDs), the size-dependent efficiency loss is commonly attributed to carrier diffusion within quantum wells (QWs). When the μLED size is sufficiently small, carriers can diffuse laterally to reach defective sidewalls, leading to non-radiative recombination. This challenges earlier assumptions of short-range carrier diffusion in InGaN/GaN QWs. However, recent studies have demonstrated the potential for long-range diffusion, prompting further investigation into how QW design and growth conditions influence carrier diffusion length and μLED efficiency. This paper contributes to this investigation by examining carrier diffusion in c-plane InGaN/GaN single QW samples using photoluminescence experiments. By varying the QW thickness, we observe an increase in diffusion length with thicker QWs, consistent with the increased radiative recombination lifetime due to the quantum confined Stark effect. This suggests that reducing QW thickness could mitigate the size-dependent efficiency loss in μLEDs. As the substrate type plays a crucial role in advancing the industrialization of μLEDs, we compare carrier diffusion in QWs grown on a substrate of different nature: sapphire, freestanding GaN, and Si (111). Our results demonstrate that the three types of substrates enable long-range diffusion. Finally, analyzing the evolution of carrier diffusion length with carrier density reveals two opposite regimes. In the high-excitation regime, carrier diffusion length decreases by increasing the excitation power, which is in agreement with previous studies and supported by a diffusion–recombination model. However, in the low-excitation regime, carrier diffusion length unexpectedly increases by increasing the excitation power.
State-of-the-art progress on artificial intelligence and machine learning in accessing molecular coordination and adsorption of corrosion inhibitors
Authors: Quadri Taiwo W. , Akpan Ekemini D. , Elugoke Saheed E. , Olasunkanmi Lukman O. , Sheetal  , Singh Ashish Kumar , Pani Balaram , Tuteja Jaya , Shukla Sudhish Kumar , Verma Chandrabhan , Lgaz Hassane , Anadebe Valentine Chikaodili , Barik Rakesh Chandra , Guo Lei , AlFantazi Akram , Mothudi Bakang M. , Ebenso Eno E.
Published: January 2025

Artificial intelligence (AI) and machine learning (ML) have attracted the interest of the research community in recent years. ML has found applications in various areas, especially where relevant data that could be used for algorithm training and retraining are available. In this review article, ML has been discussed in relation to its applications in corrosion science, especially corrosion monitoring and control. ML tools and techniques, ML structure and modeling methods, and ML applications in corrosion monitoring were thoroughly discussed. Furthermore, detailed applications of ML in corrosion inhibitor design/modeling coupled with associated limitations and future perspectives were reported.
Experimental study of laser-induced bubble collapse near a rigid wall based on the double-exposure method
Authors: Wen Haigang , Sun Yurong , Geng Siyuan , Yao Zhifeng , Zhong Qiang
Published: January 2025

Capturing and studying the process of cavitation bubble collapse can help elucidate the mechanism of cavitation erosion. In this paper, a high-spatiotemporal-resolution double-exposure photographic method is used to investigate the collapse of laser-induced cavitation bubbles at two values of the dimensionless distance from the bubble to the wall, γ = d/Rmax = 0.9 and 1.25 (where d is the vertical distance between the bubble center and the wall and Rmax is the maximum radius of the bubble). Complete high-resolution evolution sequences of bubbles near a rigid wall are captured from optical breakdown to second collapse. The generation and development of microjets and shock waves during cavitation bubble collapse are described in detail. The oscillations of the bubble near the rigid wall and the microjets and shock waves generated by the collapse are analyzed. It is shown that the presence of the rigid wall affects the development of the bubble and microjets. The microjet velocity can reach up to 64 m/s. Multiple shock waves are found to be generated by bubble collapse.
MEMS infrared light source stress optimization and reliable package design
Authors: Teng Xuesong , Yu Shenglin , Fang Cun
Published: January 2025

Aiming at the effects caused by stress and deformation on Micro-Electro-Mechanical System (MEMS) sensors, the stress distribution in the radiation area of the MEMS infrared light source is investigated, and by simulating and optimizing the thickness of the composite support film of the chip structure in COMSOL, a film layer thickness matching with lower stress and deformation for the MEMS infrared light source is derived. The utilization of the particle swarm algorithm and backpropagation neural network model allowed for the optimization of simulation data, enabling regression prediction over a broader range of thicknesses and providing a more precise depiction of the stress distribution trend. In addition, the specifications of the MEMS device help us to analyze the design of the support film thickness in the processing of the residual stress within the controllable range. To ensure the long-term stability and functionality of MEMS infrared light source chips in harsh environments, a comprehensive set of packaging schemes has been devised. Through simulations, it has been demonstrated that these packaging schemes effectively enhance the thermal efficiency of the light source while mitigating thermal stress and deformation that may arise during its operation. Consequently, this packaged configuration proves to be more advantageous for the sensor’s normal operation under challenging conditions such as rain and temperature fluctuations, as compared to utilizing a bare chip. Finally, the manufacturing flow and layout design for the MEMS infrared light source chip are provided to guide the process of chip fabrication.
Ferromagnetic permalloy/p-type boron-doped diamond Schottky barrier diodes
Authors: Kawano Makoto , Cunha Carlos , Hirama Kazuyuki , Kumakura Kazuhide , Taniyasu Yoshitaka
Published: January 2025

Ferromagnetic permalloy/p-type boron (B)-doped diamond Schottky barrier diodes (SBDs) were demonstrated. The SBDs showed a clear rectifying behavior with a high on/off ratio of over 109 and an ideality factor close to unity at 300 K. The Schottky barrier height was 2.07 eV at the permalloy/B-doped diamond interface. The permalloy Schottky electrodes did not intermix with B-doped diamond and had almost the same magnetic properties as bulk permalloy.
A study on flame reconstruction in a supersonic combustor using deep learning
Authors: Xu Wanqian , Liang Chenqiang , Qiu Hongchao , Zhang Junlong , Bao Wen
Published: January 2025

This study investigates the application of a low-order reconstruction method for image reconstruction of a scramjet combustor. In the encoding network, reconstruction performance was assessed by evaluating adjustments to sampling channel count and modifications to neural network architectures. Upsampling methods such as convolutional neural networks (CNNs), interlayer attention mechanisms, and pixel shuffle were tested in the decoder network. Furthermore, a parameter expansion strategy based on the enlargement of convolutional feature map channels was proposed and examined. The results were quantified by morphological and frequency domain analyses under tests with datasets of different equivalence ratios, suggesting the effectiveness of the scheme for flashback prediction. It was found that the reconstruction effect of 6-point sampling is close to that of continuous sampling (68 points), which is the most cost-effective among the tested schemes. By comparing different network structures, the method proposed in this paper achieves better reconstruction results than the large-parameter CNN network with a small-scale network structure.
Joint identification of aeroacoustic noises of supersonic impinging jets using particle image velocimetry and pressure-sensitive paint
Authors: Wei Chunhua , Fan Hongling , Liang Yuxiang , Tu Han , Gao Qi
Published: January 2025

The acoustic, velocity, and surface pressure fields of vertical jet impingement are studied utilizing pressure sensors, particle image velocimetry, and pressure sensitive paint measurements in parallel. Experiments are carried out at Mach numbers of 1.1 and 1.2, with corresponding Reynolds number of 5.8×105 and 6.2×105, respectively. The focus is placed on the understanding of the relationships between noise generation mechanisms within these fields. Features of fluctuation and pulsation of velocity and surface pressure are analyzed using proper orthogonal decomposition and Fourier transformation. Different types of acoustic tones are found corresponding to unique patterns in the decomposition of velocity and pressure fields. Large-scale coherent structures in the velocity field and monopoles in the surface pressure field are correlated with pure tones due to the shedding of coherent structures. Corresponding velocity fluctuations can be detected throughout the jet, reflecting the global effect of aeroacoustic resonance. Near-plate coherent flow structures and dipoles of surface pressure pulsation are associated with impingement tones. These structures account for a smaller portion of the total kinetic energy and act as a local effect near the plate. Additionally, broadband noise is presented as quadrupoles of surface pressure pulsation. The dominant modes of surface pressure exhibit morphological similarity and consistent spectral characteristics with the acoustic poles in the Lighthill analogy.
A multi-domain lattice Boltzmann mesh refinement method for non-Newtonian blood flow modeling
Authors: Daeian Mohammad Ali , Smith W. Spencer , Keshavarz-Motamed Zahra
Published: January 2025

Multi-domain grid refinement is a well-established technique in lattice Boltzmann methods. However, the method is currently limited to the Newtonian flow and no established method exists for lattice Boltzmann mesh refinement in non-Newtonian fluids. This study introduces a new method for lattice Boltzmann multi-domain mesh refinement in non-Newtonian fluids, by employing rescaling, transition, and interpolation of the relaxation frequencies across the domains interface. The method also involves a correction scheme to resolve shear rate inequality across the interface, particularly in low shear rate regions of a shear-thinning flow. To adapt the method for blood flow simulations in vascular systems, it was further extended to address three dimensional (3D) cases with curved boundary interfaces, using a ghost node technique. The method was verified in two dimensions, through Hagen–Poiseuille and lid-driven cavity flows, as well as in 3D, with steady flow in an idealized stenosis, and pulsatile flow in a patient-specific aneurysm. Results were compared with fine single-resolution simulations and existing literature, showing strong agreement. The aneurysm simulation showed good agreement with wall shear stress predictions from the fine single-resolution simulation. The relative L2 norm of wall shear stress difference between the multi-domain and fine-grid simulation were 0.006 and 0.009 at end-diastole and peak-systole, respectively. Overall, the proposed method facilitates the efficient use of computational resources through mesh refinement. Combined with the high scalability of the lattice Boltzmann method for parallel simulations—attributable to the locality of computations, including shear rate calculations—this approach is well-suited for high-fidelity investigations of blood flow in arteries.
Telecom source of tunable polarization-entanglement distribution up to 100-km for multi-user QKD over metro-area fiber-optic networks
Authors: Yadav Vikash Kumar , Venkataraman Vivek , Ghosh Joyee
Published: January 2025

The scalability of quantum communication networks requires compact, fiber-integrated, easy-to-deploy, and efficient wavelength-division-multiplexed (WDM) sources for multi-user secure key distribution. Here, we demonstrate such a multi-channel source of polarization-entangled photon pairs in the low-loss telecom C-band based on type-0 spontaneous parametric downconversion in a fiber-coupled Zn-indiffused MgO-doped periodically poled lithium-niobate (MgO:PPLN) ridge waveguide in the Sagnac configuration. The source can be easily tuned to generate the |Φ+⟩ or |Φ−⟩ Bell state in 14 channel pairs of the International Telecommunication Union dense WDM (100-GHz spacing) grid around 1550-nm with a raw fidelity of ≳89%, with a maximum value of ≳94%. The raw concurrence is ≳0.8 for both Bell states in all channel pairs, and the observed S-parameter (>2.56 ± 0.04 in all 14-channel pairs) shows a strong violation of CHSH-Bell’s inequality. The source’s suitability for long-distance entanglement transmission is also demonstrated by the successful transfer of entangled photons up to 100 km while maintaining fidelity >85% and quantum bit error rate <9%. The effect of polarization mode dispersion on entanglement distribution among remote users is also studied in detail. All these performance metrics are measured using conventional room-temperature semiconductor-based single-photon avalanche detectors, and these are the best reported with these detectors. Our highly flexible source can support up to ∼40 user pairs to communicate simultaneously, and it can be easily deployed into the current metro-area fiber-optic telecom infrastructure to form a complete WDM-based quantum communication network.
High-performance mid-infrared plasmonic bispectral routers by inverse design
Authors: Li Xuanxuan , Liu Huayou , Yang Shiyu , He Li , Su Zhijuan , Dan Yaping
Published: January 2025

In modern imaging systems, the application of multispectral imaging technologies is pervasive, furnishing an enhanced spectrum of information. Multispectral methods typically employ arrays of filters to selectively exclude light from undesired spectral bands, thus facilitating the capture of discrete narrowband data. However, the inherent multi-channel filtering process limits their energy utilization efficiency, a constraint that is magnified by the current trend of miniaturization in imaging devices. In this work, we have developed a pixel-level, metal-based, mid-infrared router by employing an inverse design method. This design achieved peak spectral efficiencies of 58.61% and 67.35% within the operational bands of 3.5–4.2 and 4.4–5 μm, respectively, and an average energy utilization efficiency across the entire operational range of 3.5–5 μm was elevated to 72%, which is 1.44 times higher than that of conventional filter-based systems. The designed routers were realized by standard nanofabrication processes that transfer the designed patterns into a gold film on a ZnS substrate. The spectral measurements show that the fabricated routers have a routing performance close to the simulation results.
Modal analysis of blood flows in saccular aneurysms
Authors: Nguyen Thien-Tam , Kasperski Davina , Huynh Phat Kim , Le Trung Quoc , Le Trung Bao
Published: January 2025

Currently, it is challenging to investigate aneurismal hemodynamics based on current in vivo data such as Magnetic Resonance Imaging or Computed Tomography due to the limitations in both spatial and temporal resolutions. In this work, we investigate the use of modal analysis at various resolutions to examine its usefulness for analyzing blood flows in brain aneurysms. Two variants of Dynamic Mode Decomposition (DMD): (i) Hankel-DMD; and (ii) Optimized-DMD, are used to extract the time-dependent dynamics of blood flows during one cardiac cycle. First, high-resolution hemodynamic data in patient-specific aneurysms are obtained using Computational Fluid Dynamics. Second, the dynamics modes, along with their spatial amplitudes and temporal magnitudes are calculated using the DMD analysis. Third, an examination of DMD analyses using a range of spatial and temporal resolutions of hemodynamic data to validate the applicability of DMD for low-resolution data, similar to ones in clinical practices. Our results show that DMD is able to characterize the inflow jet dynamics by separating large-scale structures and flow instabilities even at low spatial and temporal resolutions. Its robustness in quantifying the flow dynamics using the energy spectrum is demonstrated across different resolutions in all aneurysms in our study population. Our work indicates that DMD can be used for analyzing blood flow patterns of brain aneurysms and is a promising tool to be explored in in vivo.
Spatial arrangement of near-wall bursting process and large scales in turbulent boundary layer flows
Authors: Shi Lijuan , Zhang Jinhao , Wang Meng , Tang Zhanqi , Jiang Nan
Published: January 2025

This study explored the spatial arrangement of near-wall bursts and large-scale motions in turbulent boundary layer flows. The near-wall velocity fields were predicted and reconstructed using machine learning techniques, based on the combination dataset of inner and outer flow fields by particle image velocimetry measurements. The natural visibility graph method was then employed to map the streamwise velocity into a visibility network, generating a spatial series of network degrees. It was observed that the degree signals correspond closely with the Taylor microscale. A method for detecting bursting events was proposed based on these degree values. The relationship between small-scale bursting processes and large-scales was subsequently examined through conditional averaging, focusing on large-scale positive-to-negative and negative-to-positive zero-crossings. The findings revealed that, in the near-wall region, small-scale bursts are more intense within large-scale high-speed zones. Additionally, a spatial shift between large-scale motions and near-wall small-scale bursts was identified: small-scale bursts were displaced toward the edges of large-scale high-speed regions in the near-wall region. Furthermore, the structural organization of the outer zone was also analyzed and discussed.
Numerical study on the performance of an interventional microaxial blood pump with superhydrophobic surface
Authors: Geng Xuesong , Li Chengcheng , Ma Jianying , Qiu Huihe , Cui Guomin , Wang Ying
Published: January 2025

Unlike traditional blood pumps, interventional microaxial blood pumps are characterized by their small size, high rotational speed, and narrow gap between the impeller rim and pump housing. These features result in an unstable flow field within the pump, leading to high shear stress regions that can cause hemolysis. To improve the hydraulic efficiency of the blood pump and mitigate blood damage, this paper proposes an interventional microaxial blood pump with a superhydrophobic surface. The finite element method was used to model the axial blood pump and arterial flow field, with Navier slip boundary conditions applied to the impeller and outflow structure walls, simulating a slip length of 50 μm to represent the superhydrophobic surface characteristics. A combination of numerical simulations and hydraulic experiments was employed to evaluate the effects of the superhydrophobic surface on the pump's hydraulic performance and hemolysis characteristics. The results indicated that the designed interventional microaxial blood pump model demonstrated good blood compatibility. The superhydrophobic surface significantly reduced shear stress at the design point, with wall shear stress in the impeller and outflow structure regions decreasing by approximately 8.09%. Hydraulic efficiency increased by approximately 12.16%, and the hemolysis index decreased by about 12.60%. These findings provide valuable support for further optimization of microaxial blood pumps.
Effective and efficient modeling of the hydrodynamics for bacterial flagella
Authors: Liu Baopi , Chen Lu , Zhang Ji
Published: January 2025

The hydrodynamic interactions among bacterial cell bodies, flagella, and surrounding boundaries are crucial for understanding bacterial motility in complex environments. In this study, we demonstrate that each slender flagellum can be modeled as a series of spheres and the interactions between these spheres can be accurately characterized using a resistance matrix. This approach allows us to effectively and efficiently evaluate the propulsive effects of the flagella. Notably, our investigation into bacterial motility near a colloidal sphere reveals significant discrepancies between results derived from the twin multipole moment and those obtained through resistive force theory. Consequently, neglecting the hydrodynamic interactions among cell bodies, flagella, and colloidal spheres may lead to substantial inaccuracies. Our model simplifies bacteria into a series of spheres, making it well-suited for examining bacterial motility near spherical boundaries and the nonlinear deformation dynamics of elastic flagella.
Nonlinear hydroelastic responses of a submerged horizontal plate under focused wave conditions: A cumulative fatigue perspective
Authors: Ding Haoyu , Huang Luofeng , Zang Jun
Published: January 2025

Most current analytical research on the hydroelastic interaction between water waves and submerged horizontal elastic plates remains within the scope of linear theory due to the underdevelopment of mathematical methods for solving nonlinear problems. To address this gap, this work employs an approach that combines computational fluid dynamics (CFD) with computational solid mechanics (CSM) to dynamically simulate the fully coupled nonlinear hydroelastic interactions between ocean waves and a submerged horizontal plate. This research highlights the significance of nonlinear point responses of a submerged horizontal plate under focused wave conditions. A phase-based harmonic separation method (i.e., phase-decomposition method) is used to isolate wave amplitude and force harmonic components in complex wave scenarios. This approach allows for the clean delineation of individual harmonics from the total wave force by controlling the phase of incident focused waves and is for the first time applied to the response analysis of elastic structures. This paper successfully used the phase-decomposition method to separate the individual harmonics of the point displacement of a horizontal elastic plate, directly demonstrating the significance of nonlinear responses. Additionally, the impact of plate rigidity, which relates to natural frequency, on nonlinear responses is investigated. The results indicate that plates with a certain dimensionless plate rigidity will exhibit more significant nonlinear responses. By cleanly separating each individual harmonic response, this study provides new insights into the nonlinear hydroelastic responses of a horizontal plate interacting with water waves and offers a new perspective on fatigue analysis, underscoring the importance of nonlinearity for future engineering designs.
A new transient optimally higher-order compact scheme for computation of flow and heat transfer in nonuniform polar grids
Authors: Deka Dharmaraj , Sen Shuvam
Published: January 2025

In this work, a higher-order compact discretization is developed on the nonuniform polar grid. The discretization carries theoretically optimal third-order convergence in space and second order in time on a (5, 5) stencil. Conceptualized using the unsteady convection-diffusion equation, it is further extended to flow problems governed by the Navier–Stokes equations as well as the Boussinesq equations. The scheme developed here combines the advantages of body-fitted mesh with grid clustering, thereby making it efficient to capture flow gradients on polar grids. The scheme carries a spatial convergence of order three with temporal order of convergence being almost two. Diverse flow problems are being investigated using the scheme. Apart from a verification study, we validate the scheme by time marching simulation for the benchmark problem of a driven polar cavity and the problem of natural convection in the horizontal concentric annulus. In the process, a one-sided approximation for the Neumann boundary condition for vorticity is also presented. Finally, the benchmark problem of forced convection around a circular cylinder is tackled. The results obtained in this study are analyzed and compared with the well-established numerical and experimental data wherever available in the literature. The newly developed scheme is found to generate accurate solutions in each case.
Thermodynamic model to investigate the dielectric characteristics of phase B1 of banana-shaped liquid crystals
Authors: Singh Shubha , Singh Rajendra Kumar
Published: January 2025

In the present work, a phenomenological thermodynamic model is used to examine the dielectric properties of the B1 phase close to the I–B1 phase transition in banana-shaped liquid crystals. In this model, system's free-energy density is expanded in terms of three order parameters (OPs): the vector polarization OP (P0), scalar smectic OPs (ψ1 and ψ2), tensor orientational OP (Qij), and their coupling expressions. The core concept of the work is to elucidate the phase transition behavior of a system by considering that specific Landau coefficients, which are linked to the coupling terms of the free-energy density expansion, are influenced by changes in pressure. The variations in frequency, pressure, and temperature, which affect the intricate dielectric permittivity in the phase B1, are determined and compared to the experimental results obtained from mesogens DDB (3′−{4−[4−((S)−3,7− Dimethyloctyloxy)benzoyloxy]benzoyloxy }-4-{ 4-[4-(Decyloxy)benzoyloxy]benzoyloxy} biphenyl), DOB (3′−{4−[4−((S)−3,7− Dimethyloctyloxy)benzoyloxy]benzoyloxy }-4-{ 4-[4-(Octyloxy)benzoyloxy]benzoyloxy} biphenyl), and Compound I (3−(4′-n-octyloxybenzoyloxyphenyliminomethyl) phenyl −4″−n-octyloxy biphenylcarboxylate). In addition, we found that OP coupling terms have a significant impact on the transition parameters and have to be included while expanding the free-energy density. The suggested model adequately explains the isotropic–B1 phase interface and the characteristics of permittivity within the B1 phase. We note a very good agreement between the experimental and theoretical data for the mesogens DDB, DOB, and Compound I.
Impinging jet ventilation: Mitigating influenza transmission through partition and exhaust layout optimization
Authors: Zhang Puyang , Su Xinchao , Lu Weizhen , He Kan , Gao Guangjun , Wu Fan
Published: January 2025

This paper investigates the transmission characteristics of cough droplets from infected individuals in office environments under the influence of an impinging jet ventilation (IJV) system based on the Eulerian–Lagrangian model. The accuracy of the dispersed phase model and the IJV system simulation was validated by analyzing a single droplet evaporation model, publicly available jet experimental results, and previously simulated results. The effects of different exhaust locations, the relative positioning of the IJV system to the infected individual, and the application of partitions on the spatial propagation characteristics of droplets are explored. The results indicate that partitions exhibit a significant ability to obstruct and capture droplets. Under static conditions, they are capable of capturing over 36% of droplets generated by coughing, although this efficiency may be slightly influenced by the ventilation system. The IJV system notably affects droplet movement, with droplets progressively converging toward the upper-left corner of the room as the airflow develops. The positioning of the exhausts, in combination with the IJV system, is crucial in impeding and removing droplets. Taking into account variations in the infected individual's position, a centrally located exhaust arrangement might provide the more effective inhibition of virus droplet dispersion.