Accepted
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Abstract +
SnTe-type topological crystalline insulators (TCIs) possess multiple Dirac-like topological surface states under the mirror-symmetry protection. Superconducting SnTe-type TCIs are predicted to form multiple Majorana zero modes (MZMs) in a single magnetic vortex. For the spatially isolated MZMs, there is only one MZM in a single vortex at surface. However, experimental demonstration of coupling the two isolated MZMs by changing wire length or intervortex distance is very challenging. For the multiple MZMs, two or more MZMs can coexist together in a single vortex. Thus, the novel property is expected to significantly reduce the difficulty of producing hybridization between MZMs. Recently, the experimental evidence for multiple MZMs has been observed in a single vortex of the superconducting SnTe/Pb heterostructure. However, SnTe is a heavily p-type semiconductor which is very difficult to induce the p-type to n-type transition via doping or alloying. The study on the Fermi-level tuning of SnTe-type TCIs is critical for detecting and manipulating multiple MZMs. In this work, we report the influence of defects such as film edge, grain boundary and dislocation on the electronic property of Sn1-xPbxTe/Pb. The Sn1-xPbxTe films are prepared on the Pb (111) films grown on the Si (111) substrate by the molecular beam epitaxial technology. The structural and electronic properties of the Sn1-xPbxTe films are detected in situ by using low-temperature scanning tunneling microscopy and spectroscopy. The differential conductance tunneling spectra show that the minima of dI/dV spectra taken at the areas near the film edge, the grain boundary and the dislocation of Sn1-xPbxTe grown on Pb can be significantly changed to the energy very closed to the Fermi level or even about -0.2 eV below the Fermi level, whereas the minima of dI/dV spectra taken at the areas far away from the defects are always at about 0.2 eV above the Fermi level. It indicates that not Pb alloying but these quasi one-dimensional defects play an important role in the modification of electronic property in the Sn1-xPbxTe/Pb heterostructure. Moreover, the Pb alloying will suppress the formation of zero-energy peak in the vortex. These results are expected to develop the method of the Fermi-level tuning without need of doping or alloying for the SnTe-type topological superconducting device.
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In order to clarify the metamagnetic transition properties and corresponding crystal parameter characteristics of La0.9Pr0.1Fe12B6 alloy, as well as the accompanying magnetocaloric effects, we studied the magnetic phase transition process of the alloy induced by magnetic field and temperature, and the corresponding X-ray diffraction patterns changes, and conducted in-depth comparisons of the magnetocaloric properties under different measurement modes. The results indicate that La0.9Pr0.1Fe12B6 sample mainly consists of about 90 wt.% SrNi12B6 type structural main phase and about 10 wt.% Fe2B and α-Fe,which is consistent with references. During the zero-field increasing temperature process, the magnetic state sequence of the main phase of La0.9Pr0.1Fe12B6 alloy is antiferromagnetic (AFM)→ferromagnetic (FM)→paramagnetic (PM); during the isothermal magnetization process, three types of magnetic field-induced metamagnetic transitions occur in different temperature ranges, namely, two different transitions between AFM and FM states at low temperatures, and a transition between PM and FM states above the Curie temperature(TC). The corresponding critical magnetic field (HC) is much lower than that of the LaFe12B6 parent alloy. On the contrary, the main phase of La0.9Pr0.1Fe12B6 alloy exhibits only PM-FM transition present. This indicates that after the alloy transitions from PM state to FM state during the cooling process, even after the temperature drops to a certain value, it will not transition to AFM state. Similar phenomena also exist in other alloys of LaFe12B6 system. Based on the Néel temperature(TN) and TC obtained the ZFCW modeM-T curves, the magnetic state phase diagram of La0.9Pr0.1Fe12B6 alloy was plotted. The results indicate that as the external magnetic field increases, TC moves linearly towards higher temperatures at a rate of almost 0.48 K/kOe. Conversely, TN1 and TN2 gradually move towards lower temperatures at rates of 0.48 K/kOe and 0.26 K/kOe, respectively. The zero-field and field-variable temperature XRD patterns show that during the magnetic transition between disorder and order states of the main phase in La0.9Pr0.1Fe12B6 alloy, there is a phenomenon of magnetocrystalline coupling. As a result, in addition to the original diffraction peaks of the main phase, some new diffraction peaks that are not observable in the PM state also appear, and their intensity increases with decreasing temperature or increasing magnetic field. Through Retveld refinement XRD patterns under different conditions, it was found that the atomic occupancy of La/Pr and Fe is very stable under different environments, but the atomic occupancy of B varies greatly, which may be the main factor leading to the appearance of new diffraction peaks. In addition, in the temperature dependent magnetic entropy change curve calculated based on isothermal magnetization data in continuous measurement mode, a large magnetic entropy change can be observed near TC due to the magnetic field induced first-order metamagnetic transition of PM-FM. For example, under a magnetic field of 70kOe, the maximum magnetic entropy change near 50K can reach 19J/kg·K, and the relative cooling capacity is about 589.1J/kg. However, under the same measurement mode, the expected large magnetic entropy change due to the AFM-FM metamagnetic transition was not observed. But, when using a discontinuous measurement mode, the large magnetic entropy change accompanying the AFM-FM transition process is also observed. For example, under a magnetic field of 70kOe, the maximum magnetic entropy change near 8K can reach -12J/kg·K.
, , Received Date: 2025-06-13
Abstract +
It has been reported that the thermal conductivity of the nanofluids can be enhanced by adding Janus nanoparticles into the base fluid. Additionally, the non-spherical nanoparticles also affect the thermal characteristics of nanofluids. In this work, conical nanoparticles are designed as Janus nanoparticles with hydrophilic side and hydrophobic bottom, which are suspended in the base fluid to form cone-shaped Janus nanofluids. By using molecular dynamics (MD) simulations, it is found that the thermal conductivity of conical Janus nanofluids can be enhanced by 43.4% compared with that of the base fluid, whereas the spherical Janus nanofluids indicate an increase of 33.7% under the same volume fraction. According to MD simulation results of the RDF and diffusion coefficients of solid particle and base fluid, the increased thermal conductivity observed in conical nanofluids can be attributed to the higher liquid layer density and the enhanced Brownian motion of the conical particles. For Janus nanofluids, the asymmetrical structure of Janus nanoparticles leads to higher diffusion coefficient than that of normal particles, which enhances the colliding possibility of Janus nanoparticles with surrounding liquid molecules, thus resulting in enhanced heat transfer in Janus nanofluids. In this paper, both fixed and unfixed particles are considered to explore the influence of particle diffusion on nanofluids. Under the fixed condition, the Brownian motion of the nanoparticles is artificially excluded, while under the unfixed condition, the particle can diffuse in the base liquid. It is found that for both spherical and conical Janus nanofluids, the thermal conductivity of Janus nanofluids gradually increases with the augment of asymmetry parameter δ under unfixed conditions. However, under fixed conditions, the thermal conductivity of Janus nanofluids is almost independent of the parameter δ. Therefore, the enhanced Brownian motion of the non-spherical particles is a likely reason of the increased thermal conductivity observed in conical Janus nanofluids. The combination of non-spherical particles and Janus particles provides a promising idea for designing nanofluids with high thermal conductivity.
, , Received Date: 2025-05-08
Abstract +
GaN based Schottky barrier diode (SBD) possesses advantages including high power density, high conversion efficiency, and excellent switching characteristics. During heteroepitaxial growth of GaN, a high density of threading dislocations is inevitably introduced, which can degrade device reliability. This paper reports a low dislocation density N+/N– GaN quasi-vertical SBD fabricated on a freestanding GaN substrate. The characterization results of high-resolution X-ray diffraction and atomic force microscopy demonstrate that the high-quality epitaxial layer with a total dislocation density of 1.01 × 108 cm–2 and a root mean square surface roughness of 0.149 nm is achieved on a freestanding GaN substrate. The device prepared based on a high-quality epitaxial layer exhibits an ultra-low leakage current density of 10–5 A/cm2 at a reverse voltage of –5 V, without employing any edge termination structures or field plates or plasma treatment. Compared with the devices prepared on sapphire substrates using identical processes, the device prepared in this work reduces the reverse leakage current by four orders of magnitude. The experimental results show that the quasi-vertical GaN based SBD fabricated on a freestanding GaN substrate significantly reduces reverse leakage current and substantially enhances the overall electrical performance of the device. By employing emission-microscope (EMMI), leakage current in quasi-vertical SBD is identified to be primarily localized at the anode edge, and the underlying leakage mechanism is elucidated. Finally, temperature-dependent measurements demonstrate that the device maintains a leakage current below 10–3 A/cm2 at 100 ℃, confirming the potential of quasi-vertical SBD on freestanding GaN substrate for practical applications.
, , Received Date: 2025-07-09
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The metastable and stable liquid state thermophysical properties and rapid solidification mechanism of quaternary Fe75.6Nd10Y9B5.4 alloy with a maximum undercooling temperature of 221 K (0.14TL) are investigated using electrostatic levitation technique. The measured results indicate that the density, thermal expansion coefficient and the ratio of specific heat to emissivity of the liquid alloy comply with linear functional relationship with temperature in the range of 1402–1618 K. Molecular dynamics (MD) simulations show that the diffusion coefficients of Nd and Y elements decrease exponentially with temperature decreasing, with the former exhibiting a larger diffusion coefficient at the same temperature. When the liquid under cooling rises from 80 to 158 K, the growth velocity of primary (Nd,Y)2Fe17 phase dendrites increases from 3.8 to 5.7 mm·s−1, while exhibiting significant grain refinement effect. Meanwhile, the increased undercooling also promotes peritectic transformation, leading the volume fraction of peritectic τ1-(Nd,Y)2Fe14B phase to reach up to 75%. Once the undercooling reaches 180 K, the former peritectic τ1 phase, rather than the primary (Nd,Y)2Fe17 phase, becomes the leading phase, which nucleates and grows directly from the undercooled liquid alloy, and its growth velocity increases with undercooling from 2.6 to 11.0 mm/s. The calculation results of formation enthalpy show that the solid solution of the Y element can enhance the thermodynamic stability of the (Nd,Y)2Fe17 phase and the τ1 phase, thereby explaining the reason why the content of Y element in both phases is significantly higher than that of Nd element. Nevertheless, the content of Nd element in the τ1 phase slightly increases because its diffusion ability is stronger than that of Y if undercooling temperature is higher than 180 K.
, , Received Date: 2025-06-20
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Wall conditioning coatings—lithium (Li), boron (B) and silicon (Si) —introduced by lithiumization, boronization, or siliconization, serve as a critical strategy for suppressing fuel recycling and reducing impurity fluxes from the wall of a tokamak. These techniques directly improve plasma initiation, reproducibility, energy confinement, and operational stability in fusion devices. However, these coatings undergo both physical and chemical sputtering by boundary plasma bombardment. This erosion behavior critically determines coating lifetime and, consequently, long-pulse plasma performance. To evaluate the influence of physical sputtering on coating durability and to compare material-specific differences, binary collision approximation (BCA) simulations are conducted to investigate the physical sputtering behaviors of Li, B, and Si coatings. Carbon (C) and tungsten (W) substrates are also modeled to assess interface effects. The results reveal the significant differences in sputtering yields between Li, B, and Si in incident angles and deuterium energies. Owing to its low surface binding energy, lithium exhibits the highest sputtering yield at large angles and low energies, while silicon, with the highest atomic number, presents the highest sputtering yield at small angles and high energies. Sputtering yields of carbon-based and tungsten-based coatings vary with angle and energy, driven by differences in deuterium backscattering between the interface sputtering and substrate sputtering. Notably, for tungsten-based coatings, the sputtering yields increase dramatically at specific energies. This occurs because tungsten’s high surface binding energy causes incident deuterium atoms to reflect off the tungsten interface and then collide with coating elements. Consequently, when the energy transferred to the surface element is higher than its sputtering threshold, the sputtering yield increases. Additionally, increasing incident fluence modifies the target composition, leading to corresponding changes in the sputtering yields of coating materials. In summary, coating materials should be selected according to the expected angle distribution and energy distribution of the incident plasma particles. To suppress the abrupt yield increase observed in tungsten substrates at specific energies, the coatings must be sufficiently thick. These findings provide a theoretical basis for selecting conditioning materials and optimizing wall conditioning strategies in fusion devices.
, , Received Date: 2025-07-10
Abstract +
The asymmetric wetting Janus fiber membrane exhibits many unique properties when interacting with liquids due to its significant difference in wetting properties on both sides. Therefore, it has broad application prospects in fields such as microfluidics and biomedicine. The directional transport of droplets is one of the key functions of Janus fiber membranes, and its transport mechanism and regulation rules are crucial for practical applications. However, there is currently insufficient research on how wettability gradient and pore structure regulate the directional transport behavior of droplets. In this study, a two-phase flow phase-field model is established, and the reliability of the model is validated through droplet transport experiments conducted on plasma-assisted fabricated Janus fiber membranes. Building on this foundation, the directional transport behavior of droplets within the membrane is systematically investigated. The results show that the spontaneous transport of droplets from hydrophobic side to hydrophilic side is driven by a synergistic effect of surface free energy gradient, Laplace pressure difference, and capillary force. It is found that hydrophobic layer thickness, hydrophilic layer thickness, wettability gradient, and pore structure are key factors in regulating transport efficiency. Compared with traditional structures, Janus fiber membranes with wettability gradients can significantly improve the directional transport speed of droplets, and the wettability of the hydrophilic side shows a significant positive correlation with transport velocity. Although increasing pores can accelerate droplet transport, it simultaneously reduces the steady-state spreading area on the hydrophilic side. This study provides an important theoretical basis for optimizing the Janus fiber membrane structure and achieving efficient and precise fabrication of droplets.
, , Received Date: 2025-04-02
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Superconducting quantum interference device (SQUID) is one of the most sensitive flux sensors and is critical in fields such as biomagnetism, low-field nuclear magnetic resonance (NMR), and geophysics. In this paper, an integrated magnetoencephalography (MEG) SQUID chip is investigated in detail, which consists of a magnetometer and two gradiometers. The SQUID and pick-up coils are fabricated on different-sized wafers. The SQUID is fabricated on a commercial silicon substrate using micro- and nano-fabrication processes, including thin-film growth, i-line stepper photolithography, and reactive ion etching (RIE). The sub-micron Josephson junction technology is employed to achieve a junction size of 0.7 μm×0.7 μm with a junction capacitance of only 0.05 pF. The pick-up coil is designed as a single-turn coil for a magnetometer and a planar first-order gradient coil for a gradient sensor. The MEG SQUID chips are tested in a well-shielded chamber with the helium-liquid temperature (4.2 K). Customized low-voltage noise readout circuit and source measure units are used to characterize the magnetic field white noise, current-voltage (I-V) characteristics, and voltage modulation amplitude of 171 SQUID channels. The results show that 81% of the SQUID chips exhibit the lower magnetic field noise (< 5 $ {\text{fT/}}\sqrt {{\text{HZ}}} $), and the high modulation amplitudes (in a range of 80–120 μV) with the low working currents of 15–20 μA, yielding a wafer yield rate of 78%. In summary, the SQUIDs show excellent performance in terms of magnetic field white noises, modulation amplitudes, and working currents, which are suitable for the very weak magnetic signal detection. One of future studies will focus on optimizing the SQUID chip fabrication process to minimize performance variations between chips on the same wafer.
, , Received Date: 2025-04-22
Abstract +
Thermal accumulation under high output power density is one of the key bottlenecks faced by GaN-based power devices. The nanocrystalline diamond (NCD) passivation layer strategy plays a crucial role in improving heat dissipation in high-power GaN devices, while the existing studies focus on GaN-based HEMT. In this study, nanocrystalline diamond films with a thickness of 380–450 nm are grown on Si-based AlGaN/GaN heterostructure materials using a microwave plasma chemical vapor deposition (MPCVD) system. Consequently, lateral Schottky barrier diode devices with NCD passivation are fabricated, and their electrical and thermal properties are investigated. The results show that the DC forward characteristics of the NCD-passivated diodes are essentially the same as those of devices without NCD passivation. Moreover, dynamic voltage tests indicate that the NCD passivation layer significantly mitigates current collapse in GaN devices at high frequencies. Under a –20 V DC bias and a pulse voltage of 2.5 V, the current density degradation is only 2.6%, whereas traditional devices almost completely degrade. Thermal imaging microscopy under varying DC power levels shows that thermal failure occurs at an output power density of approximately 4 W/mm for traditional devices, while NCD-passivated devices can reach around 7.5 W/mm. The electrical degradation behaviour of NCD passivated device is also tested under long-time reverse bias. This work demonstrates for the first time the application of nanocrystalline diamond passivation to thermal management of GaN-based power diodes, and clearly demonstrates the potential of this strategy in non-HEMT power device applications.
, , Received Date: 2025-05-30
Abstract +
The fiber Bragg grating has the characteristics of anti-electromagnetic interference, electrically passive operation, multi-point sensing, corrosion resistance, and compact size. An ultra-narrow linewidth transmission peak can be formed by introducing a π phase shift at the center of uniform fiber Bragg grating. But this PSFBG with an ultra-narrow linewidth is very sensitive to the input optical intensity. The photothermal effect generated by the input light inside the grating will cause the frequency shift, which will degrade the measurement precision of grating. At the same time, the frequency drift of the laser itself will also increase the measurement error. In this paper, a high-precision strain measurement method is proposed by using the PSFBG with an ultra-narrow linewidth based on the frequency-stabilized laser. The incident laser is attenuated to a single-photon level to eliminate the photothermal effect in the PSFBG. The laser frequency is stabilized to the PSFBG with an ultra-narrow linewidth of 38 MHz by using the single-photon modulation technology. The influence of low-frequency flicker noise is eliminated through 9-kHz high-frequency modulation. The filter bandwidth of lock-in amplifier is 312.5 Hz with the integration time and filter slope of 300 μs and 18 dB, respectively. The signal-to-noise ratio of error signal from the lock-in amplifier is 34. By tuning the resonant cavity length of the laser with the error signal, the output laser frequency is stabilized to the Bragg frequency of the PSFBG with an ultra-narrow linewidth of 38 MHz. The laser frequency fluctuation is limited to 4 MHz within 1000 s. The response sensitivity of Bragg wavelength to external strain in a range of 0 to 30 με is 1.2 pm/με, with a standard error of 0.023 pm/με, and the linear fitting correlation coefficient is R2 = 0.997. Due to the random drift of Bragg wavelength, caused by the environment temperature fluctuations, the corresponding strain measurement precision is 0.05 με. The high-precision strain measurement by using the PSFBG with an ultra-narrow linewidth based on the frequency-stabilized laser is achieved, which will play an important role in the field of aerospace engineering, civil engineering, transportation engineering, energy engineering, mechanical and equipment manufacturing, etc.
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Abstract +
Entanglement detection and classification of multipartite systems remain the key topics in the field of quantum information and science. In this work, we take advantage of the nature that quantum Fisher information (QFI) can witness multipartite entanglement to comprehensively investigate the entanglement detection and classification of multi-qubit WW states immersed in a white noise environment. In the situation of local operation, by combining the information of the known quantum state, we have presented a criterion with visibility for witnessing the genuine multipartite entanglement and another for identifying the presence of quantum entanglement. Specifically, with respect to the 5-qubit WW state and 6-qubit WW state, due to the fact that the maximum QFI of their splitting-structure states exceeds that of the original states, it is infeasible to strictly establish a criterion for detecting the genuine multipartite entanglement. However, we delineate the scope for inferring the possible entanglement structures. Furthermore, it is found that as the number of qubits increases, the conditions for witnessing the genuine multipartite entanglement become increasingly strict, while those for detecting the existence of entanglement grow relatively more relaxed. Taking into account the likelihood of the crosstalk between neighboring qubits during the local operations on the multipartite systems in experiments, we employ the Lipkin-Meshkov-Glick (LMG) model to explore the entanglement classification of diverse multi-qubit multipartite states. It is found that with the increasing interaction strength, even for the strong white noise, the WW states can still be distinguished, thereby resolving the challenge of managing the entanglement classification under local operation. Besides, as the interaction strength continues to increase, the task of entanglement classification becomes more straightforward. This fully shows the superiority of nonlocal operations over local operations in the aspect of entanglement classification.
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The growing demands of high-speed imaging, aerospace, and optical communication have driven intensive research on broadband photodetectors with high sensitivity and fast response. Twodimensional (2D) materials, featuring atomic-scale thickness, tunable bandgaps, and excellent carrier transport properties, are regarded as ideal candidates for next-generation optoelectronics. However, their limited light absorption and intrinsic recombination losses remain key challenges. This review provides an overview of recent progress in 2Dmaterial-based broadband photodetectors. First, the fundamental optoelectronic properties of 2D materials, including bandgap modulation, carrier dynamics, and light - matter interactions, are discussed to clarify their broadband detection potential. Representative material systems - such as narrow-bandgap semiconductors, 2D topological materials, and perovskites - are summarized, demonstrating detection capabilities spanning from ultraviolet to mid-infrared regions. To overcome intrinsic limitations, four optimization strategies are highlighted: heterostructure engineering for efficient charge separation and extended spectral response; defect engineering to introduce mid-gap states and enhance sub-bandgap absorption; optical field enhancement through plasmonic nanostructures and optical cavities to improve responsivity; and strain engineering for reversible band structure tuning, particularly suited for flexible devices. These strategies have enabled remarkable improvements in responsivity, detectivity, and bandwidth, with some devices achieving ultrabroadband detection and multifunctionality. In summary, 2D materials and their hybrids have shown great promise for broadband photodetection, with advances spanning from material innovation to device architecture optimization. The reviewed strategies - heterostructure integration, defect modulation, optical field enhancement, and strain engineering - collectively demonstrate the diverse pathways to overcome intrinsic limitations and boost device performance. Looking forward, the rational combination of these approaches is expected to further expand the detection window, improve sensitivity, and enable multifunctional operation, thereby paving the way toward nextgeneration broadband photodetectors with versatile applications in imaging, sensing, and optoelectronic systems
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Abstract +
Diagnostics of combustion flow fields in aeroengines, scramjets, and related systems play a crucial role in understanding combustion mechanisms, assessing combustion stability and performance, and represent a major challenge in the development of advanced propulsion technologies. Among the non-intrusive diagnostic approaches, laser absorption spectroscopy has become one of the most representative techniques. In particular, tunable diode laser absorption spectroscopy (TDLAS) offers advantages such as a compact system architecture, ease of miniaturization, strong environmental adaptability, and the capability of simultaneous temperature and concentration measurements. By employing multiple laser beams intersecting at different angles and collecting absorption spectra along various paths, the two-dimensional distribution of flow-field parameters can be reconstructed using computed tomography (CT) algorithms.
However, conventional nonlinear tomographic algorithms based on polynomial models encounter difficulties when reconstructing flow fields with steep gradients. To address this issue, we propose a hybrid reconstruction method that integrates a regional weighting mechanism. In this framework, the polynomial model is combined with a Gaussian radial basis function (RBF) model, and a regional weight matrix is iteratively updated in an adaptive manner. The regional weight matrix is determined by introducing perturbations into the current temperature field and jointly considering its temperature gradient. This design allows the hybrid model to capture global features while enhancing its ability to resolve local details. In addition, a regional weight regularization term is incorporated into the residual function to further improve reconstruction accuracy.
To validate the proposed approach, numerical simulations were conducted on three representative combustion field distributions, with comparisons against polynomial model, RBF model, and traditional algebraic reconstruction technique (ART) algorithms. Results demonstrate that the hybrid model achieves higher representational capability and reconstruction accuracy, with maximum temperature and concentration errors reduced to 3.31% and 7.13% (for the Top-Hat case), respectively. A scanning TDLAS measurement platform and a thermocouple measurement platform were built on a standard McKenna burner to experimentally verify the method. The reconstructed distributions exhibit good consistency with the experimental results, with a deviation of only 10 K between the reconstructed central temperature at 1800 K and the thermocouple measurement. These findings verify the effectiveness of the proposed method and highlight its potential as a reliable tool for combustion field diagnostics in propulsion systems.
However, conventional nonlinear tomographic algorithms based on polynomial models encounter difficulties when reconstructing flow fields with steep gradients. To address this issue, we propose a hybrid reconstruction method that integrates a regional weighting mechanism. In this framework, the polynomial model is combined with a Gaussian radial basis function (RBF) model, and a regional weight matrix is iteratively updated in an adaptive manner. The regional weight matrix is determined by introducing perturbations into the current temperature field and jointly considering its temperature gradient. This design allows the hybrid model to capture global features while enhancing its ability to resolve local details. In addition, a regional weight regularization term is incorporated into the residual function to further improve reconstruction accuracy.
To validate the proposed approach, numerical simulations were conducted on three representative combustion field distributions, with comparisons against polynomial model, RBF model, and traditional algebraic reconstruction technique (ART) algorithms. Results demonstrate that the hybrid model achieves higher representational capability and reconstruction accuracy, with maximum temperature and concentration errors reduced to 3.31% and 7.13% (for the Top-Hat case), respectively. A scanning TDLAS measurement platform and a thermocouple measurement platform were built on a standard McKenna burner to experimentally verify the method. The reconstructed distributions exhibit good consistency with the experimental results, with a deviation of only 10 K between the reconstructed central temperature at 1800 K and the thermocouple measurement. These findings verify the effectiveness of the proposed method and highlight its potential as a reliable tool for combustion field diagnostics in propulsion systems.
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Abstract +
HfOX memristors have emerged as one of the most promising candidates for next-generation non-volatile memory due to their low operating voltage, excellent endurance, and cycling characteristics. However, the randomness in the formation and rupture of oxygen vacancy conductive filaments within HfOX thin films leads to a relatively dispersed threshold voltage distribution and poor stability. Therefore, improving the stability of HfOX devices by modulating oxygen vacancies is of significant research importance. In this study, three groups of W/HfOX/Pt devices were prepared using magnetron sputtering with argon-to-oxygen ratios of 30:20, 40:10 and 45:5, respectively. XPS results indicated that the 45:5 device has the highest oxygen vacancy concentration(25.59%). All three groups exhibited bipolar resistive switching behavior. Among the three W/HfOX/Pt devices, the device with argon-to-oxygen ratio of 45:5 demonstrated the best overall performance: over 200 I-V cycles, a switching ratio of ~103, excellent data retention within 104 seconds, and a concentrated threshold voltage distribution. Analysis of the conduction mechanisms revealed that the device follows a space-charge-limited current (SCLC) mechanism in the high-resistance state and exhibits Ohmic conduction behavior in the low-resistance state. In the initial state, there is a high density of oxygen vacancies near the nucleation region of the conductive filament, which shortens the effective migration path of oxygen vacancies. Under an applied electric field, negatively charged oxygen ions migrate toward the top electrode, while oxygen vacancies gradually accumulate from the bottom electrode to the top electrode, leading to the formation of continuous conductive filaments. A higher oxygen vacancy concentration facilitates the development of robust and structurally more stable conductive filaments, thereby enhancing the uniformity of resistive switching and device reliability. This study reveals the critical role of oxygen vacancy modulation in the performance of HfOX memristors and provides an effective pathway for developing high-performance and highly reliable resistive random-access memory.
Abstract +
This study systematically investigates the bouncing behavior and dynamics of microbubbles under ultrasound excitation within a rigid capillary. It aims to provide quantitative insights into their oscillation characteristics, migration trajectories, and phase modulation mechanisms for applications in microfluidics, contrast-enhanced ultrasound imaging, and controlled drug delivery. A high-speed imaging system was employed to track the motion of single-, double-, and triple-bubble systems in a viscoelastic medium inside a capillary with a 0.5 mm inner diameter. Under a 28 kHz ultrasound field, bubble dynamics were captured at 100,000 frames per second. Image processing techniques, including dynamic threshold segmentation and morphological operations, were applied to extract bubble contours and centroid trajectories. Spectral analysis via Fast Fourier Transform (FFT) was performed to identify oscillation frequencies and modulation characteristics. Experimental results showed that a single bubble exhibits periodic lateral migration with oscillation frequency slightly below the driving frequency, alongside an asymmetric sideband distribution in its spectrum. In the two-bubble system, five distinct dynamic stages were identified: initial suppression, accelerated migration, interaction dominance, position exchange, and a secondary approach to the wall. The bubbles oscillated at a common dominant frequency of 27.32 kHz but maintained phase difference. Modulation sidebands of approximately 0.3 kHz were observed, indicating nonlinear coupling. The three-bubble system exhibited more complex spatiotemporal evolution, including sequential migration and transitions between triangular and mirror-symmetric configurations. A notable sideband at 0.1 kHz suggested that multi-bubble synergy enhances nonlinear behavior. The tube diameter and fluid viscosity were found to influence the bouncing period through added mass effects and viscous energy dissipation, respectively. The period increased significantly with decreasing tube diameter and decreased with reducing fluid viscosity. Theoretical modeling incorporated the mirror bubble effect into the coupled Keller-Miksis equations to account for wall confinement, successfully simulating the oscillation and translation of confined microbubbles. Numerical analysis further indicated that interbubble distance, wall proximity, and medium viscosity modulate the system's dynamics. Specifically, the bubble resonance frequency is regulated by inter-bubble distance and wall confinement. The two-bubble system exhibits both in-phase and out-of-phase modes, with the latter being more sensitive to distance variations. Near the wall, the oscillation frequency decreases, and the phase difference attenuation accelerates. Increased medium viscosity weakens the phase coupling between bubbles, an effect particularly pronounced for smaller bubbles. This study not only enhances the understanding of multi-bubble synergistic effects in confined spaces but also provides a theoretical foundation and technical reference for optimizing ultrasound contrast agents, designing microfluidic devices, and developing targeted therapies in biomedicine.
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