bluuebunny/crossref_metadata_2025 huggingface dataset:
High-performance photothermal effect in MOCVD grown topological insulator Sb2Te3 nanograting
Authors: Li Xin , Wan Zhengfen , Zhang Yinan , Zhang Yachao , Hu Yanlei , Yue Zengji , Kumar Arun , Cecchini Raimondo , Longo Massimo
Published: October 2023

Photothermal energy has been widely used in high-tech applications, such as heating/cooling systems, bio-imaging, bio-sensing, and medical therapies. However, conventional photothermal materials have narrow photo-absorption bandwidth and low photothermal conversion efficiency. Innovative materials that can more efficiently harvest photothermal energy are highly demanded. Topological insulator materials with excellent optical properties hold great potential in photo-absorption and photothermal conversion. This work investigated and engineered photo-absorption and photothermal effect in Sb2Te3 topological insulator nanograting. The TI material was grown by metal-organic chemical vapor deposition to exploit the benefits of the process, yielding high material quality and large deposition areas. Through a meticulous process encompassing material synthesis, engineering, and characterization, highly absorptive Sb2Te3 topological insulator nanograting and efficient photothermal conversion have been achieved. This research contributes to the advancement of the fundamental knowledge of light–matter interaction and photothermal effects in topological insulator materials. The outcomes of this study can benefit the development of efficient photothermal materials for high-performance nano-energy and biomedical technologies.
Molecular dynamics simulation of ultrasound cavitation occurring in copper–water nanofluid
Authors: Zhang Dongwei , Duan Cheng'ao , Guan Jian , Chen Songxuan , Ha Xiaoliang , Liu Tianlu , Liu Deping , Tang Songzhen
Published: October 2023

It is necessary to reveal the impact of nanoparticles on ultrasonic cavitation phenomena in nanofluids, which is conducive to the heterogeneous nucleation applications of ultrasonic cavitation. In this work, the ultrasonic cavitation processes in pure water and nanofluids were simulated by molecular dynamics. Then, the effect of nanoparticles on ultrasonic cavitation was investigated by adding alternate positive and negative pressure waves. After that, the formation of critical bubbles in cavitation and the collapse of nanobubbles by shock waves were studied by using Voronoi mosaic method and rigid body model, respectively. Finally, the regenerated nanobubbles were analyzed after the collapse of nanobubbles. The results show that the nanoparticles could promote the formation of nanobubbles, and consequently, the nano-jets and nanoparticles movement occur during the collapse of nano-bubbles. Additionally, more tiny cavities generated after the collapsing of nanobubbles and the number of nanobubbles during second cycle will be larger than that of the first cycle. As a result, some of these cavities promote the generation of multiple ultrasonic cavitation bubbles in the subsequent ultrasonic cycle. This leads to the chain reaction effect of ultrasonic cavitation phenomenon occurring in nanofluids.
Effect of Robin boundary conditions on the onset of convective torsional flows in rotating fluid spheres
Authors: Sánchez Umbría J. , Net M.
Published: October 2023

Torsional flows are preferred at the onset of thermal convection in fluid spheres with stress-free and perfectly conducting boundary conditions, in a narrow region of the parameter space for Prandtl numbers Pr≲0.9 and ratios Pr/Ek=O(10), with Ek being the Ekman number. In this case, the transport of heat to the exterior is supposed instantaneous. When the thermal conductivity of the internal fluid is large, and the external convective heat transfer or radiative emissivity is low, the heat transmission is less efficient, and the thermal energy retained in the interior increases, enhancing the onset of convection. This study is devoted to analyzing the combined influence of the thermal conductivity and external conditions (temperature and resistance to heat transport) on the onset of the torsional convection by taking a Robin boundary condition for the temperature at the surface of the sphere. It is shown, by means of the numerical computation of the curves of simultaneous transitions to torsional flows and Rossby waves, that when the heat flux through the boundary decreases, the region where the axisymmetric flows are preferred shrinks, but it never strangles to an empty set. It has been found that with adequate scalings the curves delimiting the transition to torsional flows, and those of the critical Rayleigh number, Rac, and the frequencies of the modes vs Ek become almost independent of the parameter of the Robin boundary condition.
Temporal correlation between hard x rays and radio emissions in the MHz and GHz frequency ranges generated by a laboratory high-voltage discharge
Authors: Parkevich E. V. , Khirianova A. I. , Khirianov T. F. , Baidin I. S. , Shpakov K. V. , Rodionov A. A. , Bolotov Ya. K. , Ryabov V. A. , Ambrozevich S. A. , Oginov A. V.
Published: October 2023

We investigate the temporal correlation between very-high-frequency (VHF, at frequencies of the order of 10–100 MHz), ultrahigh-frequency (UHF, at frequencies within 1–6 GHz), and x-ray (with photon energies more than 10 keV) emissions, which accompany the development of a high-voltage discharge initiated in a long gap at voltages up to 1 MV. The x-ray and UHF emissions are found to emerge starting approximately from the prepulse current onset observed before the discharge gap breakdown and both gradually decay coming to this instant. The UHF emission spectrum is represented with frequencies up to 6 GHz, with the highest spectral power being achieved within 1–2 GHz. The radio emission power drops sharply at frequencies below 1 GHz and increases closer to 150 MHz with the highest spectral power of VHF radiation being reached within 60–90 MHz. The VHF emission can appear before the discharge current and UHF emission onsets in the form of 100-ns-long prepulses, and its intensity significantly increases as the UHF emission starts. The analysis of the temporal correlation between x rays, VHF, and UHF radiations, discharge current, and voltage waveforms indicates that the generation mechanisms of the discharge electromagnetic radiations are difficult to be interpreted in terms of the developing or colliding streamer concepts.
Experimental investigation of flame state transition in a gas turbine model combustor by analyzing noise characteristics
Authors: Mardani Amir , Bahonar Hosna , Beige Amir A.
Published: October 2023

Hysteresis of flame transition from lifted (V-shaped) to flat form is studied in a gas turbine model combustor by using acoustic measurements in connection with infrared thermometry and visual recordings. The impacts of varying several parameters including the shape of the fuel injector, flow rates, confinement (i.e., combustion chamber), and air preheat on flame shape transition and the corresponding acoustic behavior are studied using experimental measurements. It is shown that the flat flame produces noise at two dominant frequencies (related to the acoustics and hydrodynamic instabilities), and these frequencies could be used for flame shape transition prediction from the V-shaped flame, which produces different frequencies. Time–frequency wavelet analysis of the generated noise shows highly non-stationary behavior with mode hoppings for both flame states. The results show that the flame state transition hysteresis is highly dependent on the parameters that change the details of flow near the baseplate, and in this way, the higher flow rates, air preheat, and round slit injector intensify the transition hysteresis. Also, the presence of the combustion chamber was shown to be very effective in reducing the studied hysteresis.
Excitation of an upper hybrid wave by Laguerre–Gaussian pulse in plasma with a density ramp and electron acceleration
Authors: Kad Proxy , Singh Arvinder
Published: October 2023

In this paper, the excitation of an upper hybrid wave (UHW) by propagation of a Laguerre–Gaussian (LG) laser pulse in an exponential density ramp plasma has been investigated in relativistic regime. A uniform static magnetic field was externally applied perpendicular to the propagation of the laser. The spatiotemporal dynamics of laser pulse have been studied by two coupled differential equations obtained via the moment theory approach. The propagating laser pulse excites an electron plasma wave, which further interacts with the laser pulse in the presence of applied transverse magnetic field and generates an UHW. The excited UHW further traps the plasma electrons and accelerates them. It has been observed that the presence of density ramp affects the laser dynamics, excited UHW, and electron acceleration. The applied magnetic field and modes of LG laser have also shown significant effect on electron acceleration. Energy gain of the order of 400 MeV/mm has been obtained for electrons.
Theoretical and numerical analysis of the flow through a diffuser/nozzle element in pulsatile laminar conditions
Authors: Peruzzo Paolo
Published: October 2023

Diffuser/nozzle pipes produce a directional flow resistance that is often exploited in microcirculation to generate a pumping action. This work presents an approximate time-dependent theoretical solution based on the mechanical energy conservation equation to predict the laminar flow rate through an ideal diffuser/nozzle pump. The theoretical solution is then used to characterize the dimensionless parameters that control the dynamics of the valveless pump in the pulsatile flow regime. A suitable numerical model is also implemented to solve the flow in a parametrized two-dimensional axial-symmetric domain subjected to an oscillating pressure, and its results are used to assess the theoretical solution. The pump dynamics and the main model parameters, such as the energy-loss coefficients, result in the following dependence on the ratios between the viscous force, the advective inertia, and the temporal inertia, i.e., the Reynolds (Red), Womersley (Wod), and Strouhal (St) numbers referred to throat diameter. In particular, The Womersley number plays an essential role in controlling the global energy loss when Red < 100. The flow transition is also investigated and found when Red exceeds a critical value, which increases with Wod. Finally, the pump efficiency is found to reach its maximum when the convective and temporal inertia become comparable, i.e., St=O(1), consistent with the observed range of St in real-world diffuser/nozzle pumps. This optimum range of functioning of the pump is also observed for cerebrospinal pulsatile flow in the Sylvius aqueduct, suggesting that the modeled mechanism is used to promote or enhance cerebrospinal fluid circulation.
Hydrodynamics of turbidity currents evolving over a plane bed
Authors: Mahato Rajesh K. , Dey Subhasish , Ali Sk Zeeshan
Published: October 2023

In this paper, we investigate the hydrodynamics of turbidity currents evolving over a plane bed. The analytical framework encompasses the depth-averaged conservation equations for fluid mass, sediment mass, momentum, and turbulent kinetic energy (TKE). The analysis incorporates self-similar distributions of streamwise velocity, sediment concentration, and TKE. Using the self-similar distributions of streamwise velocity and sediment concentration, the distributions of turbulent diffusivity, Reynolds shear stress, and TKE production rate are determined. The analytical model of turbidity currents enables the prediction of streamwise evolutions of flow depth, depth-averaged velocity, depth-averaged sediment concentration, and depth-averaged TKE. The self-acceleration and subsidence of turbidity currents are found to depend on the initial conditions. Additionally, the model results demonstrate the sensitivity of turbidity current hydrodynamics to grain size and longitudinal bed slope. Importantly, increased grain size and longitudinal bed slope contribute to enhanced self-acceleration, leading to a decrease in the subsidence rate of turbidity currents. The model predictions satisfactorily capture the available experimental data.
Analog programming of CMOS-compatible Al2O3/TiO2−x memristor at 4.2 K after metal-insulator transition suppression by cryogenic reforming
Authors: Mouny Pierre-Antoine , Dawant Raphaël , Galaup Bastien , Ecoffey Serge , Pioro-Ladrière Michel , Beilliard Yann , Drouin Dominique
Published: October 2023

Exploration of memristors' behavior at cryogenic temperatures has become crucial due to the growing interest in quantum computing and cryogenic electronics. In this context, our study focuses on the characterization at cryogenic temperatures (4.2 K) of TiO2−x-based memristors fabricated with a CMOS-compatible etch-back process. We demonstrate a so-called cryogenic reforming (CR) technique performed at 4.2 K to overcome the well-known metal-insulator transition (MIT), which limits the analog behavior of memristors at low temperatures. This cryogenic reforming process was found to be reproducible and led to a durable suppression of the MIT. This process allowed to reduce by ∼20% the voltages required to perform DC resistive switching at 4.2 K. Additionally, conduction mechanism studies of memristors before and after cryogenic reforming from 4.2 to 300 K revealed different behaviors above 100 K, indicating a potential change in the conductive filament stoichiometry. The reformed devices exhibit a conductance level that is 50 times higher than ambient-formed memristor, and the conduction drop between 300 and 4.2 K is 100 times smaller, indicating the effectiveness of the reforming process. More importantly, CR enables analog programming at 4.2 K with typical read voltages allowing to store up to 4 bits of information on a single CR memristor. Suppressing the MIT improved the analog switching dynamics of the memristor leading to ∼250% larger on/off ratios during long-term depression (LTD)/long-term potentiation (LTP) resistance tuning. This enhancement opens up the possibility of using TiO2−x-based memristors to be used as synapses in neuromorphic computing at cryogenic temperatures.
Two surface multipactor with non-sinusoidal RF fields
Authors: Iqbal Asif , Wen De-Qi , Verboncoeur John , Zhang Peng
Published: October 2023

Two-surface multipactor with a Gaussian-type waveform of rf electric fields is investigated by employing Monte Carlo simulations and 3D electromagnetic particle-in-cell simulations. The effects of the full width at half maximum (FWHM) of the Gaussian profile on multipactor susceptibility and the time dependent dynamics are studied. The threshold peak rf voltage, as well as the threshold time-averaged rf power per unit area for multipactor development, increases with a Gaussian-type electric field compared to that with a sinusoidal electric field. The threshold peak rf voltage and rf power for multipactor susceptibility increase as the FWHM of the Gaussian profile decreases. Compared to sinusoidal RF operation, the expansion of multipactor susceptibility bands is observed. In the presence of space charge, a high initial seed current density can shrink the multipactor susceptibility bands. The effect of space charge on multipactor susceptibility decreases as the FWHM of the Gaussian profile decreases. Decreasing the FWHM of the Gaussian electric field can reduce the electron population corresponding to the strength of the multipactor at saturation, at fixed time-averaged input power.
Over-barrier photoelectron emission with Rashba spin–orbit coupling
Authors: Tiang Bi Hong , Ang Yee Sin , Ang L. K.
Published: October 2023

We develop a theoretical model to calculate the quantum efficiency (QE) of photoelectron emission from materials with the Rashba spin–orbit coupling (RSOC) effect. In the low temperature limit, an analytical scaling between QE and the RSOC strength is obtained as QE ∝(ℏω−W)2+2ER(ℏω−W)−ER2/3, where ℏω, W, and ER are the incident photon energy, work function, and the RSOC parameter, respectively. Intriguingly, the RSOC effect substantially improves the QE for strong RSOC materials. For example, the QE of Bi2Se3 and Bi/Si(111) increases, by 149% and 122%, respectively, due to the presence of strong RSOC. By fitting to the photoelectron emission characteristics, the analytical scaling law can be employed to extract the RSOC strength, thus offering a useful tool to characterize the RSOC effect in materials. Importantly, when the traditional Fowler–Dubridge model is considered, the extracted results of the prefactor a1 in QE may substantially deviate from the actual values by ∼90%, thus highlighting the importance of employing our model to analyze the photoelectron emission especially for materials with strong RSOC. These findings provide a theoretical foundation for the design of photoemitters using Rashba spintronic materials.
The sensitivity of PT-symmetric LC wireless sensors around an exceptional point
Authors: Zhou Bin-Bin , Liu Wei-Dong , Dong Lei
Published: October 2023

Inductor–capacitor (LC) wireless sensors are highly useful in applications that require them to be powered remotely and operated in rotating parts or harsh environments. Recent advances in the fields of parity-time (PT) symmetry proposed in the context of quantum mechanics have revealed that the performance of the LC wireless sensors can be improved. The basic sensing principle is to detect changes of the sensing capacitance, i.e., perturbation in PT- symmetry, through monitoring the frequency shift, i.e., eigenvalues in PT-symmetry. Here, we have analyzed and compared the sensitivity of the LC wireless sensors biased under an exact phase and near an exceptional point (EP). The frequency splitting responses of the PT-symmetric LC wireless sensors with the symmetric gain-loss arrangement are presented under asymmetric and symmetric perturbation, respectively. It shows that the asymmetric perturbation breaks PT-symmetry, leading to complex eigenvalues. In the exact phase, the high frequency response of two normal mode frequencies to symmetric perturbation shows the optimum sensitivity. The resulting eigenvalues splitting is proportional to the square root of perturbation near the EPs for both asymmetric and symmetric perturbation. The sensitivity to asymmetric perturbation is higher than that to symmetric perturbation. Finally, a capacitive humidity sensor was used to demonstrate the analysis.
Gas-particle flows in a microscale shock tube and collection efficiency in the jet impingement on a permeable surface
Authors: Ejtehadi Omid , Mankodi Tapan K. , Sohn Ilyoup , Kim Byoung Jae , Myong R. S.
Published: October 2023

We investigate the flow physics of non-equilibrium gases in interaction with solid particles in a microscale shock tube and the collection efficiency in the jet impingement on a permeable surface. One interesting application of flows in shock tubes at low pressures or micro-shock tubes is needle-free injection technology where drug particles are delivered by shock waves. To investigate such problems, a new two-fluid model system coupled with second-order Boltzmann–Curtiss-based constitutive relationships for modeling a non-equilibrium gas was developed. We were specifically interested in how rarefaction affects the complex wave patterns observed in dusty gas flows and the role of bulk viscosity in diatomic and polyatomic gases exposed to moving shocks. Simulation results demonstrated how significantly the bulk viscosity can affect the topology of the solution in the Sod shock tube problem. Counter-intuitive flow features were noted, resulting from bulk viscosity effects and the incapability of the first-order theory, even when Stokes' hypothesis was abandoned (i.e., the Navier–Fourier model). After detailed analyses in one-, two-, and three-dimensional space for simplified flow problems, a case was designed to represent a needle-free injection device. In addition, a new concept of “collection efficiency” was introduced that quantifies the efficiency of drug delivery in the two-phase jet impingement on the skin. We also derived a new “vorticity transport equation” that takes the bulk viscosity and multiphase effects into account. Based on the new equation, the time evolution of vorticity growth rates was analyzed for all the contributing terms in the equation.
Heterodimensional superlattices based on two-dimensional materials
Authors: Lv Lu , Zhou Jiadong , Gao Yanfeng
Published: October 2023

Two-dimensional (2D) superlattices are promising candidates for future technological applications due to their unique electronic structure and exotic properties. Heterodimensional superlattices, consisting of 2D and other dimensional (0D, 1D, 2D, 3D) structural units, extend the applications of 2D superlattices to spintronics, thermoelectrics, and energy storage. In this perspective, we highlight the recent progress in heterodimensional superlattices based on 2D materials. First, we introduce the classification and properties of heterodimensional superlattices, including 3D/2D, 1D/2D, 2D/0D, and hybrid multidimensional superlattices. Second, the potential applications of 2D heterodimensional superlattices are discussed. Finally, we point out the current challenges and provide an outlook in the field of heterodimensional superlattices.
Screened plasmons of graphene near a perfect electric conductor
Authors: Moradi Afshin , Türker Tokan Nurhan
Published: October 2023

Screened plasmon properties of graphene near a perfect electric conductor (PEC) are investigated taking into account the retardation effects. A detailed discussion of the dispersion relation of the mentioned screened plasmonic waves is presented and illustrated graphically using classical electrodynamics and a linearized hydrodynamic model that includes Fermi correction. The result indicates that for realistic wavenumbers, the dispersion relation of plasmonic waves of isolated graphene is almost unaffected by the Fermi correction, while this correction is an important factor for the screened plasmons of graphene near a PEC, where it increases the frequency of surface waves. The results show that near the graphene neutrality point, the surface wave has linear dispersion with a universal speed close to vF/2. Such linear dispersion for surface waves (also known as energy waves) appears to be a common occurrence when splitting of plasma frequencies occurs, e.g., in the electron–hole plasma of graphene [Zhao et al., Nature 614, 688 (2023)]. Furthermore, analytical expressions for the energy parameters (the power flow, energy density, and energy velocity) of screened plasmons of the system are derived. Also, the analytical expressions are derived and analyzed for the damping function and surface plasmon and electromagnetic field strength functions of surface waves of the system with small intrinsic damping.
Controllable Nernst and Seebeck effects in graphene with O-shaped Kekulé structure
Authors: Zhang Peipei , Wang Chao , Li Yu-Xian , Zhai Lixue , Song Juntao
Published: October 2023

The Nernst and Seebeck effects in graphene with uniform Kekulé lattice distortion have been studied using the tight-binding model combined with the nonequilibrium Green's function method. Numerical results of this work showed that due to the electron–hole symmetry, the Nernst coefficient is an even function of the Fermi energy, while the Seebeck coefficient is an odd function regardless of the magnetic field. The Nernst and Seebeck coefficients show peaks when the Fermi energy crosses the Landau levels at high magnetic fields or crosses the transverse subbands at the zero magnetic fields. The peak height can be very large when the Fermi energy approaches the Dirac point, the Seebeck coefficient can reach about 0.78 mV/K, and the Nernst coefficient can reach about 0.95 mV/K at the corresponding hopping energy modification parameter δ=0.03 and T=0.009t/kB≈288 K. When δ=0.08 and T=0.024t/kB≈766 K, the Seebeck coefficient (or Nernst coefficient) is still up to about 0.78 mV/K (or 0.95 mV/K). This suggests that tunable Seebeck and Nernst coefficients can be achieved because the bandgap is a function of the corresponding hopping energy modification parameter δ. Experimentally, δ can be modulated by changing the type and amount of atoms adsorbed on graphene. In strong magnetic fields, the Nernst coefficient does not depend on the chirality of the nanoribbon.
High-speed shock–boundary-layer interaction over deformed surfaces
Authors: Kokkinakis Ioannis W. , Drikakis Dimitris , Spottswood S. Michael , Brouwer Kirk R , Riley Zachary B.
Published: October 2023

This paper concerns the interaction of an oblique shock wave with a supersonic turbulent boundary layer over a thin panel surface, leading to shock–boundary layer interaction and panel buckling. We have performed high-order numerical simulations featuring various static two-dimensional surface deformations typically encountered in experiments. The deformation amplitudes we examined were at least half the height of the incoming turbulent boundary layer thickness. The results show that along the panel midspan, where the maximum deformation amplitude is located, the mean and root mean square pressure are affected by about 10%. Cases for which the pressure at the shock–boundary layer interaction was increased relative to the planar case showed to decrease downstream, and vice versa. Despite the weak response to the mean pressure amplitude, the mean pressure surface contour plots reveal that the streamwise, particularly the spanwise distribution, is affected more noticeably. For example, the surface deformation modes are shown to disrupt the spanwise constant mean pressure, forming higher (or lower) values at either the panel's midspan or edges, depending on the mode. Moreover, the surface curvature leads to a characteristic bending of the spanwise distribution, which can be concave or convex depending on the deformation mode. Analysis of the Reynolds stress anisotropy componentality at different heights from the buckled surface reveals a similar spanwise response of the turbulent velocity fluctuations. The results suggest that the deformation rate plays an important role alongside the deformation amplitude in the turbulent layer and shock–boundary layer interaction.
Allelopathic effect of phenolic acids in various extracts of wheat against Fusarium wilt in faba bean
Authors: Yang Siyin , Zheng Yiran , Guo Yuting , Cen Zixuan , Dong Yan
Published: October 2023

Allelopathy is the main reason for disease control in intercropping systems. The effects of different extracts, root secretions and phenolic acids of wheat and faba bean on Fusarium oxysporum f. fabae (FOF) growth were studied to explore the allelopathy mechanism of wheat in disease control of faba bean. Various extracts and root exudate of faba bean were promoted but those of wheat inhibited the growth and reproduction of FOF. High-performance liquid chromatography revealed significant differences in the contents of phenolic acids in the various extracts and root exudate of wheat and faba bean. The total content of syringic acid (SA) was much higher, but that of other five phenolic acids were lower in wheat than in faba bean. The in vitro addition of these phenolic acids revealed that cinnamic acid (CA), p-hydroxybenzoic acid (PHBA), benzoic acid (BA), vanillic acid (VA) and ferulic acid (FA) exhibited significant promoting effects and SA exhibited strong inhibitory effects on the growth of FOF. These results suggest that the inhibitory effect of various extracts and root exudates from wheat on FOF growth may be due to differences in phenolic acid content and high levels of SA.
Comment on ‘Horizon-scale tests of gravity theories and fundamental physics from the Event Horizon Telescope image of Sagittarius A*’
Authors: Tsukamoto Naoki
Published: October 2023

Vagnozzi et al constrained the additional parameter of spacetimes with a photon sphere from the observation of the shadow of Sagittarius A* under the assumption that a distance to the Sagittarius A* and its mass parameter was estimated from other observations. They claimed that a Damour–Solodukhin wormhole with an additional parameter λ is not an asymptotically-flat spacetime and that they gave the first robust observational constraint on the parameter λ of the Damour–Solodukhin wormhole. However, they overlooked the fact that: (A) the Damour–Solodukhin wormhole spacetime is asymptotically flat, (B) the throat of the Damour–Solodukhin wormhole works as an effective photon sphere for

λ
>

2

/

2

, and (C) not only a usual mass parameter but also the parameter λ contributes the mass of the Damour–Solodukhin wormhole. Because of the overlook (C), we realize that their constraint on the parameter λ is invalid. This is because their method corresponds to the following way: They estimated the mass parameter from the other observations under the assumption λ = 0 even though the value of the parameter λ strongly affects the determination of the mass parameter, and then, they used the value of the mass parameter to constrain λ from the observation of the shadow. We conclude that we should constrain the mass parameter and λ from the shadow observation and other observations without the assumption λ = 0.
Optical dipole micro-trap for atoms based on crossed planar photonic waveguides
Authors: Ovchinnikov Yuri B , Ayi-Yovo Folly Eli , Spampinato Alessio
Published: October 2023

Optical dipole micro-traps for atoms based on constructive superposition of two-colour evanescent light waves, formed by corresponding optical modes of two crossed suspended photonic rib waveguides, are modelled. The main parameters of the traps for rubidium atoms, such as potential depth, tunnelling rates of atoms from the trap and coherence time of the trapped atoms are estimated.
Influence of operating conditions on electron density in atmospheric pressure helium plasma jets
Authors: Xu Wenwen , Lu Yonghang , Yue Xiaofeng , Liu Xiaoping , Wu Zhengwei
Published: October 2023

In recent years, atmospheric-pressure plasma jets have emerged as valuable tools in many application areas, including material modification, environmental remediation and biomedicine. Understanding the discharge characteristics of these plasma jets under various operating conditions is crucial for optimizing process outcomes. This paper presents a two-dimensional fluid model for numerical simulation to study the variation in electron density within an atmospheric-pressure helium plasma jet under different operating conditions. The investigated parameters include helium gas flow rate, voltage amplitude, needle-to-ring discharge gap, and relative permittivity of the dielectric tube. The results reveal that the peak electric field and electron density initially occur at the wall of the dielectric tube and subsequently shift towards the head of the propagating jet. Gas flow rate has minimal impact on the electron density throughout the plasma jet, whereas increasing the needle-to-ring discharge gap significantly decreases the average electron density within the jet. In addition, an increase in the voltage amplitude and the relative permittivity of the dielectric tube enhances the electric field within the discharge space, thereby increasing the electron density in the plasma jet. These findings underscore the importance of understanding the correlation between electron density and operating conditions to precisely control plasma jets and enhance material treatment effectiveness for specific applications.
Thermal transport and phonon localization in periodic h-GaN/h-AlN superlattices
Authors: Chen Jiao , Chen Guofu , Wang Zhaoliang
Published: October 2023

The widely observed non-diffusive phonon thermal transport phenomenon in nanostructures is largely attributed to classical size effects, which ignore the characteristic of phonon wave. In this context, the crossover transition process from incoherent to coherent phonon transport in two-dimensional heterogeneous periodic h-GaN/h-AlN superlattices is demonstrated using a non-equilibrium molecular dynamics approach, where the localization behavior of thermal phonons is particularly significant. The results show that the thermal transport of the superlattice structure is affected by a combination of structural parameters and temperature. The thermal conductivity (TC) of the superlattice decreases and then increases as the interface density increases. Phonon-interface scattering dominates the incoherent phonon transport, while local phonons modulate the transport in the coherent region. Thus, the competition between phonon wave and particle properties causes the transition from incoherent to coherent phonon transport. In addition, as the TC valley depth slows down with increasing system temperature, the scattering of medium and high frequency phonons is enhanced and the phonon lifetime decreases. Research on localized phonons in superlattices provides theoretical support for thermal transport regulation in basal low-dimensional materials.
Thickness detection of anisotropic variable cross-section bone based on ultrasonic guided waves
Authors: Liu Pingxin , Zhang Zhiyuan , Xu Juan , Xue Chaolong , Li Bing
Published: October 2023

We measured cortical bone thickness of long bones by ultrasonic guided waves for diagnosis of osteoporosis. Current studies were limited to the detection of isotropic cortical bone with uniform thickness, which did not reflect the actual situation. This paper considered the anisotropic cortical bone and proposed an inversion method for measuring the thickness of variable cross-section cortical bone. Firstly, the propagation characteristics of guided waves in cortical bone could be verified by experimentally measuring the guided wave velocity. Then, the inversion method used the A0 mode wavenumber distribution to characterize the thickness of bone plates. Through error analysis, when the signal frequency remains constant, the thinner the cortical bone thickness to be measured, the more accurate the measurement results are. For the thickness inversion of the quantitative experiments in vitro bovine tibia, the error was within 1.1 mm for the oblique bone plate and within 0.9 mm for the concave bone plate. The thickness inversion error of the transverse isotropic assumption decreased by 7.8% compared to the isotropic assumption, which is more realistic for the cortical bone. The method can effectively invert the local thickness of cortical bone, thus providing a reliable basis for evaluating bone health status.
Hyperthermic triggers for drug delivery platforms
Authors: Alarcón-Segovia Lilian C , Morel Maria R , Daza-Agudelo Jorge I , Ilardo Juan C , Rintoul Ignacio
Published: October 2023

Electromagnetic fields can penetrate aqueous media in a homogeneous and instantaneous way, without physical contact, independently of its temperature, pressure, agitation degree and without modifying their chemical compositions nor heat and mass transfer conditions. In addition, superparamagnetic biomaterials can interact with electromagnetic fields by absorbing electromagnetic energy and transforming it in localized heat with further diffusion to surrounding media. This paper is devoted to the exploration of the potential use of hyperthermic effects resulting from the interaction between externally applied electromagnetic fields and superparamagnetic nanoparticles as a trigger for controlled drug release in soft tissue simulating materials. Gelatin based soft tissue simulating materials were prepared and doped with superparamagnetic nanoparticles. The materials were irradiated with externally applied electromagnetic fields. The effects on temperature and diffusion of a drug model in water and phosphate buffer were investigated. Significant hyperthermic effects were observed. The temperature of the soft tissue simulating material resulted increased from 35 °C to 45 °C at 2.5 °C min−1. Moreover, the release of an entrapped model drug reached 89%. The intensity of the hyperthermic effects was found to have a strong dependency on the concentration of superparamagnetic nanoparticles and the power and the pulse frequency of the electromagnetic field.
Nonlinearity induced negative Poisson’s ratio of two-dimensional nanomaterials
Authors: Wei Peng , Yang Dong-Jian , Xue Yixuan , Jiang Jin-Wu
Published: October 2023

Materials exhibiting a negative Poisson’s ratio have garnered considerable attention due to the improved toughness, shear resistance, and vibration absorption properties commonly found in auxetic materials. In this work, the nonlinear effect on the Poisson’s ratio was derived theoretically and verified by first-principle calculations and molecular dynamics simulations of two-dimensional nanomaterials including graphene and hexagonal boron nitride. The analytic formula explicitly shows that the Poisson’s ratio depends on the applied strain and can be negative for large applied strains, owing to the nonlinear interaction. Both first-principle calculations and molecular dynamics simulations show that the nonlinear effect is highly anisotropic for graphene, where the nonlinearity-induced negative Poisson’s ratio is much stronger for the strain applied along the armchair direction. These findings provide valuable insights into the behavior of materials with negative Poisson’s ratios and emphasize the importance of considering nonlinear effects in the study of the Poisson’s ratio of two-dimensional materials.
TMB+-mediated etching of urchin-like gold nanostructures for colorimetric sensing
Authors: Huang Zhicheng , Krishnakumar Harish , Denomme Ryan , Liu Juewen
Published: October 2023

The morphology-dependent localized surface plasmon resonance of gold nanostructures has been widely utilized for designing sensors. One method relies on the color change of gold nanoparticles upon etching. In previous work, TMB2+ oxidized from 3,3′,5,5′-tetramethylbenzidine (TMB) was found to etch gold nanorods (AuNRs), leading to a spectrum of different colors. However, the preparation of TMB2+ needs the addition of a strong acid and other harsh conditions. Herein, a new colorimetric biosensing platform was developed using urchin-like gold nanoparticles (AuNUs). Compared with AuNRs, the etching of AuNUs can happen under mild conditions by TMB+ at pH 6, protecting enzymes and proteins from denaturation. The role of CTAB surfactant was dissected, and its bromide ions were found to be involved in the etching process. Based on these observations, a one-step colorimetric detection of H2O2 was realized by using horseradish peroxidase and H2O2 to oxidize TMB. Within 30 min, this system achieved a detection limit of 80 nM H2O2. This work offered fundamental insights into the etching of anisotropic gold nanostructures and optimized the etching conditions. These advancements hold promise for broader applications in biosensing and analytical chemistry.
Assessment of dosimetric sensitivity enhancement of xylenol orange Fricke gel by AuNPs: optical and MR imaging investigation
Authors: Lima I S , Silveira M A , Pavoni J , Guidelli J E , Garrido E C S , Baffa O
Published: October 2023

Metallic nanoparticles, such as gold (Au, Z = 79) and silver (Ag, Z = 47) nanoparticles (AuNPs and AgNPs, respectively), possess strong surface plasmonic resonance (SPR) and high atomic number, which makes them ideal candidates for enhancing dosimeter sensitivity. In this study, we have inserted different mass percentages (from 0 to 0.015 wt%) of AuNPs into a gelatinous Fricke-xylenol-orange (FXO-f) gel matrix and irradiated it with doses ranging from 2 to 32 Gy, using a source of x-ray of low energy with an effective energy of 42 keV. Optical absorption increased significantly; sensitivity gains of up to 50% were achieved for the FXO-f gel matrix containing 0.011 wt% AuNPs. To elucidate the mechanism underlying this increased sensitivity, we also evaluated FXO-f gel matrixes containing AgNPs. AgNPs insertion into the FXO-f gel matrix did not enhance sensitivity, which suggested that the AgNPs plasmonic absorption band and the FXO-f gel matrix absorption band at 441 nm overlapped, to increase absorption even after the gel matrix was irradiated. To visualize the dose distribution, we recorded optical tomography and acquired 3D reconstruction maps. In addition, we analyzed the dose enhancement factor (DEF) by using magnetic resonance images. AuNPs insertion into the FXO-f gel matrix resulted in a DEF gain of 1.37, associated with the photoelectric effect originating from the increased number of free radicals.
Dispersion of an inhomogeneous sandwich plate having imperfect interfaces and supported by the Pasternak foundation
Authors: Asif Muhammad , Nawaz Rab , Ibrahim Nuruddeen Rahmatullah
Published: October 2023

The purpose of this investigation is to see the dispersion of an inhomogeneous sandwich plate with imperfect interfaces between the layers and supported by the two parameters Pasternak foundation under long-wave low-frequency conditions. The governing equation of motion has been considered from the perspective of an anti-plane shear propagation to achieve simplicity. The overall cut-off frequency and the exact dispersion relation (EDR) are computed. In the context of the structure under investigation, one material contrast setup has been considered. The shortened polynomial dispersion relation, which corresponds to the EDR under material contrast setup, has been reported and investigated further. Additionally, the variational effects of the Pasternak foundation parameters as well as the interface imperfect parameter on the lowest dispersion curve subject to the long-wave low-frequency domain have been investigated using numerical simulations and graphical representations. This study is noteworthy because it sheds light on the behavior of elastic waves in multilayered structures and may be utilized to enhance the layout of three-layered structures used in a variety of industrial fields. Furthermore, we have provided the optimum values of the involved parameters to control and confine the sandwich plate’s vibration within the long-wave low-frequency regime.
Tunability of Andreev levels in a spin-active Ising superconductor/half-metal Josephson junction
Authors: Acharjee Saumen , Boruah Arindam , Dutta Nimisha , Devi Reeta
Published: October 2023

We study the Andreev levels, supercurrent and tunnelling conductance in a clean Ising superconductor (ISC)/half-metal (HM)/ISC Josephson junction (JJ) with spin-active interfaces using Bogoliubov–de Gennes equations. We theoretically demonstrate the effect of spin mixing, spin flipping processes and spin–orbit coupling (SOC) of the ISC on Andreev bound states spectra, the current phase relation and tunnelling conductance in a transparent and opaque barrier limit. We witness an additional splitting of the Andreev levels due to the SOC of the ISC and

0
−
π

transition for different barrier magnetic moments. Also, different φ-junctions can be achieved by tuning the strength of the barrier magnetic moment and spin mismatch angle. Moreover, a possible

0
−
π

transition can also be achieved for a SOC stronger than the chemical potential of the ISC using suitable control parameters. The tunnelling conductance is found to be dependent on the spin mismatch angle. A finite subgap conductance is also observed, indicating different probabilities of Andreev reflected electrons and holes in the presence of SOC. Furthermore, anomalous Andreev levels are observed for different HM length scales, signifying their role in the tunability of the φ-phase JJ.
Optical N-plasmon: topological hydrodynamic excitations in graphene from repulsive Hall viscosity
Authors: Sun Wenbo , Van Mechelen Todd , Bharadwaj Sathwik , Boddeti Ashwin K , Jacob Zubin
Published: October 2023

Edge states occurring in Chern and quantum spin-Hall phases are signatures of the topological electronic band structure in two-dimensional (2D) materials. Recently, a new topological electromagnetic phase of graphene characterized by the optical N-invariant was proposed. Optical N-invariant arises from repulsive Hall viscosity in hydrodynamic many-body electron systems, distinct from the Chern and Z
2 invariants. In this paper, we introduce the topologically protected edge excitation—optical N-plasmon of interacting many-body electron systems in the topological optical N-phase. These optical N-plasmons are signatures of the topological plasmonic band structure in 2D materials. We demonstrate that optical N-plasmons exhibit unique dispersion relations, stability against various boundary conditions, and edge profiles when compared with the topologically trivial edge magneto plasmons. Based on the optical N-plasmon, we design an ultra sub-wavelength broadband topological hydrodynamic circulator, which is a chiral quantum radio-frequency circuit component crucial for information routing and interfacing quantum–classical computing systems. Furthermore, we reveal that optical N-plasmons can be effectively tuned by the neighboring dielectric environment without breaking the topological properties. Our work provides a smoking gun signature of topological electromagnetic phases occurring in 2D materials arising from repulsive Hall viscosity.
Understanding the Predication Mechanism of Deep Learning through Error Propagation among Parameters in Strong Lensing Case
Authors: Fan Xilong , Wang Peizheng , Li Jin , Yang Nan
Published: October 2023

The error propagation among estimated parameters reflects the correlation among the parameters. We study the capability of machine learning of “learning” the correlation of estimated parameters. We show that machine learning can recover the relation between the uncertainties of different parameters, especially, as predicted by the error propagation formula. Gravitational lensing can be used to probe both astrophysics and cosmology. As a practical application, we show that the machine learning is able to intelligently find the error propagation among the gravitational lens parameters (effective lens mass M

L
and Einstein radius θ

E
) in accordance with the theoretical formula for the singular isothermal ellipse (SIE) lens model. The relation of errors of lens mass and Einstein radius, (e.g., the ratio of standard deviations


=

σ

M

L

ˆ

/

σ

θ

E

ˆ

) predicted by the deep convolution neural network are consistent with the error propagation formula of the SIE lens model. As a proof-of-principle test, a toy model of linear relation with Gaussian noise is presented. We found that the predictions obtained by machine learning indeed indicate the information about the law of error propagation and the distribution of noise. Error propagation plays a crucial role in identifying the physical relation among parameters, rather than a coincidence relation, therefore we anticipate our case study on the error propagation of machine learning predictions could extend to other physical systems on searching the correlation among parameters.
Fundamentals and applications of photonic waveguides with bound states in the continuum
Authors: Yu Zejie , Gao He , Wang Yi , Yu Yue , Tsang Hon Ki , Sun Xiankai , Dai Daoxin
Published: October 2023

Photonic waveguides are the most fundamental element for photonic integrated circuits (PICs). Waveguide properties, such as propagation loss, modal areas, nonlinear coefficients, etc., directly determine the functionalities and performance of PICs. Recently, the emerging waveguides with bound states in the continuum (BICs) have opened new opportunities for PICs because of their special properties in resonance and radiation. Here, we review the recent progress of PICs composed of waveguides with BICs. First, fundamentals including background physics and design rules of a BIC-based waveguide will be introduced. Next, two types of BIC-based waveguide structures, including shallowly etched dielectric and hybrid waveguides, will be presented. Lastly, the challenges and opportunities of PICs with BICs will be discussed.