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We present a GeSe/SnSe van der Waals heterojunction fabricated using the wet transfer technique. GeSe and SnSe were synthesized via a low-temperature and atmospheric-pressure chemical vapor deposition method. The GeSe/SnSe heterostructure photodetector demonstrates remarkable rectification characteristics, boasting a rectification ratio of 102, along with an exceptionally low dark current, indicating minimal power consumption. Furthermore, it exhibits a broad optical response, spanning from the visible spectrum (450 nm) to the near-infrared (1064 nm). Under 808 nm laser illumination and reverse bias, the device achieves a responsivity of 19.82 A/W, a detectivity of 4.74 × 109 Jones, and an external quantum efficiency of 3048.32%. Notably, the GeSe/SnSe heterojunction photodetector also exhibits self-powered characteristics, with a responsivity of 0.11 mA/W and a detectivity of 5.44 × 106 Jones at zero bias voltage, accompanied by a fast response time of 23/61 ms (rise/fall). These findings underscore the effectiveness of the GeSe/SnSe heterojunction as a strategy for near-infrared photodetectors to simultaneously achieve low power consumption, high photoresponsivity, and self-powered photodetection, which is promising for optoelectronic device applications. [ABSTRACT FROM AUTHOR]

Coherent optical phonon (COP) and coherent acoustic phonon (CAP) play vital roles in probing ultrafast dynamics across various materials and systems. Their applications range from metamaterial diagnosis to manipulating ferroelectric polarization and self-trapping of carriers in perovskites. However, the inherently small signals associated with COP and CAP pose challenges in extracting valuable information. In this paper, we address this challenge by presenting a numerical differential method for signal amplification and deduction of phonon dephasing time. In addition, application of this method has been demonstrated in a superlattice system, establishing the validity and effectiveness of this technique. [ABSTRACT FROM AUTHOR]

The single-phase polycrystalline NiCoV medium-entropy alloy (MEA) has shown ∼1 GPa yield strength, surpassing most single face centered cubic alloys. This excellent strength has been theoretically devoted to the special solid solution hardening effect of V. However, the intrinsic reasons for this excellent strengthening effect of V in high-/medium-entropy alloys are still less experimentally explored. To this end, we here investigated the solid solution hardening effect of V in the NiCoV system. The results showed that the solid hardening mechanism changes from lattice distortion to atomic volume mismatch when the V content exceeds 6 at. %. Particularly, the increase in V content increases the Hall–Petch coefficient of NiCoV MEAs significantly. The combination of efficient grain boundary hardening and atomic volume mismatch hardening leads to the excellent yield strength of concentrated NiCoV. [ABSTRACT FROM AUTHOR]

This paper investigates the processes of droplet condensation and self-propelled jumping on microcolumn-structured superhydrophobic surfaces with various size parameters. Using a three-dimensional (3D) multiphase lattice Boltzmann method, a novel phenomenon of secondary coalescence jumping is identified, and the underlying mechanisms are analyzed in detail. The simulation results show that wettability has a significant influence on droplet jumping. As the hydrophobicity of the surface increases, the droplets tend to jump from the substrate. However, structure parameters, such as the microcolumn spacing and height, have non-monotonic effects on droplet jumping. The structure parameters determine whether droplet coalescence occurs under the bottom–bottom droplet coalescence mode or the bottom–top droplet coalescence mode. Bottom–bottom droplet coalescence is shown to promote droplet jumping. Based on the simulation results and kinetic analysis, the optimal spacing-to-width and height-to-width ratios of the microcolumns for droplet jumping are found to be approximately 0.6 and 1.0, respectively. We believe the results of this work will provide valuable guidance in the design of self-cleaning surfaces and enhancing heat transfer efficiency. [ABSTRACT FROM AUTHOR]

Erythrocyte dynamics and hemorheology exist inextricably connection. In order to further explore the population dynamics of erythrocytes in non-physiological shear stress flow and its microscopic hemolysis mechanism, this study improved the coarse-grained erythrocytes damaged model and established the hemoglobin (Hb) diffusion model based on the transport dissipative particle dynamics. The whole blood hemolysis simulation results showed that the red blood cells near the active shear side were more likely to be damaged, and most of the escaping cytoplasm was also concentrated in this side. After the destruction and relaxation of erythrocytes, the cell membrane presents a pathological state of relaxation and swelling. Moreover, we built a deep learning network for recognizing erythrocyte morphology and analyzing the erythrocyte population change rule in non-physiological shear stress flow. In this study, the clues of the blood shear-thinning effect were found from erythrocyte dynamics and coarse-grained simulation. After the shearing starts, the coin-stacked erythrocytes are depolymerized. Then, the overturned double concave erythrocytes changed into multilobe erythrocytes. When the flow shear stress gradually increases, most erythrocytes show an ellipsoidal tank-treading movement along the shear direction. Changes in erythrocyte morphology can reduce flow resistance, showing a phenomenon of the whole blood shear-thinning effect. [ABSTRACT FROM AUTHOR]

It is important to accurately identify and measure in-focus droplets from shadowgraph droplet images that typically contain a large number of defocused droplets for the research of multiphase flow. However, conventional in-focus droplet identification methods are time-consuming and laborious due to the noise and background illumination in experimental data. In this paper, a deep learning-based method called focus-droplet generative adversarial network (FocGAN) is developed to automatically detect and characterize the focused droplets in shadow images. A generative adversarial network framework is adopted by our model to output binarized images containing only in-focus droplets, and inception blocks are used in the generator to enhance the extraction of multi-scale features. To emulate the real shadow images, an algorithm based on the Gauss blur method is developed to generate paired datasets to train the networks. The detailed architecture and performance of the model were investigated and evaluated by both the synthetic data and spray experimental data. The results show that the present learning-based method is far superior to the traditional adaptive threshold method in terms of effective extraction rate and accuracy. The comprehensive performance of FocGAN, including detection accuracy and robustness to noise, is higher than that of the model based on a convolutional neural network. Moreover, the identification results of spray images with different droplet number densities clearly exhibit the feasibility of FocGAN in real experiments. This work indicates that the proposed learning-based approach is promising to be widely applied as an efficient and universal tool for processing particle shadowgraph images. [ABSTRACT FROM AUTHOR]

Increasingly heart failure patients need to use Ventricular Assist Devices (VADs) to keep themselves alive. During treatment, hemolysis is an inevitable complication of interventional devices. The most common method for evaluating mechanical hemolysis is to calculate Hemolysis Index (HI) by the power-law formula. However, the HI formula still has obvious flaws. With an intention of further understanding the phenomenon of mechanical hemolysis in non-physiological flow, our study developed a coarse-grained erythrocyte destruction model at the cellular scale and explored the mechanism of the single erythrocyte shear destruction utilizing the Dissipative Particle Dynamics, including the erythrocyte stretching destruction process and the erythrocyte non-physiological shearing destruction process. In the process of stretching and shearing, the high-strain distribution areas of erythrocytes are entirely different. The high-strain areas during stretching are concentrated on the central axis. After the stretch failure, the erythrocyte changes from fusiform to shriveled biconcave. In the shear breaking process, the high strain areas are focused on the erythrocyte edge, causing the red blood cells to evolve from an ellipsoid shape to a plate shape. In addition to the flow shear stress, the shear rate acceleration is also an important factor in the erythrocyte shear damage. The erythrocyte placed in low shear stress flow is still unstably destroyed under high shear rate acceleration. Consequently, the inclusion of flow-buffering structures in the design of VADs may improve non-physiological hemolysis. [ABSTRACT FROM AUTHOR]

The starting processes of under-expanded free jets with nozzle pressure ratios of 2.15, 2.7, and 3.4 are systematically analyzed by large-eddy simulations, and the unified laws of the evolution of the screech frequency and the screech mode in the starting jet are given. Through the development of vortices, the critical time points of the generations of screech tones are investigated. The wavenumber spectra and dispersion relations are employed, showing that the screech feedback loops in the different starting jets are all closed by the neutral waves excited by the interaction between the Kelvin–Helmholtz wavepacket and shock cells of different wavenumbers. The screech frequency prediction during the starting process is put forward for the first time, which is achieved by combining the neutral acoustic wave mode with wavenumber differences between shock cells and the Kelvin–Helmholtz wavepacket. Spectral proper orthogonal decomposition is applied to explain the reason for the change in the interaction mechanism during the starting process. [ABSTRACT FROM AUTHOR]

In this work, a new three-dimensional sessile droplet freezing model, involving the ice fraction and ice distribution after the droplet recalescence, is established based on the many-body dissipative particle dynamics with the energy conservation method for the first time. The proposed model is verified by comparing it with experimental results, and the accuracy of this model increases as the ice distribution becomes more non-uniform after recalescence. Furthermore, the effects of surface contact angle, droplet volume, surface temperature, and droplet supercooling degree on the freezing process are investigated in detail. The numerical results demonstrate that the angle of ice tips maintains a constant under various conditions. The upper and lower limits of solidification time under specific conditions are derived, and the droplet solidification time decreases linearly with the increase in supercooling. In addition, the average droplet solidification rate decreases with the increase in droplet volume, contact angle, and surface temperature, and the surface temperature is demonstrated to have the greatest influence on the solidification rate. Emphatically, we put forward an empirical formula, as a function of droplet volume, contact angle, droplet supercooling degree, and surface temperature, to predict the freezing time of a sessile supercooled droplet. [ABSTRACT FROM AUTHOR]

Helicon plasma density may show a non-monotonic dependence on the magnetic field at low strength, so-called "low-field peak (LFP)." We presented the multiple LFPs and the formation mechanism in argon helicon plasmas in this paper. Propagating conditions of helicon (H) and Trivelpiece–Gould (TG) waves in collisional plasmas were calculated based on the dispersion relation. It is demonstrated that there are two mechanisms during mode transition responsible for LFP, i.e., resonance of H- and TG-waves and anti-resonance of TG-wave. Especially, H-TG resonance of the highest axial mode in the helicon plasma results in a density jump rather than a density peak due to the mode transition from non-wave to co-H/TG-wave mode. Higher plasma density in lower magnetic fields is helpful for achievement of multiple LFPs in argon helicon plasmas. [ABSTRACT FROM AUTHOR]

For the shadowgraphy techniques with a single camera, it is difficult to accurately obtain the shape, size, and depth location of the droplets out of focus due to the defocus blur. This paper proposed a deep learning-based method to recover the sharp images and infer the depth information from the defocused blur droplets images. The proposed model comprising of a defocus map estimation subnetwork and a defocus deblur subnetwork is optimized with a two-stage strategy. To train the networks, the synthetic blur data generated by the Gauss kernel method are utilized as the input data, which mimic the defocused images of droplets. The proposed approach has been assessed based on synthetic images and real sphere blur images. The results demonstrate that our method has satisfactory performance both in terms of depth location estimation and droplet size measurement, e.g., the diameter relative error is less than 5% and the location error is less than 1 mm for the sphere with a diameter of more than 1 mm. Moreover, the present model also exhibits considerable generalization and robustness against the transparent ellipsoid and the random background noise. A further application of the present model to the measurement of transparent water droplets generated by an injector is also explored and illustrates the practicability of the present model in real experiments. The present study indicates that the proposed learning-based method is promising for the three-dimensional (3D) measurement of spray droplets via a combination of shadowgraphy techniques using a single camera, which will greatly reduce experimental costs and complexity. [ABSTRACT FROM AUTHOR]

In many fluid experiments, we can only obtain low-spatial high-temporal resolution flow images and high-spatial low-temporal resolution flow images due to the limitation of high-speed imaging systems. To solve this problem, we proposed a degradation and super-resolution attention model (D-SRA) using unsupervised machine learning to super-resolution reconstruct high resolution (HR) time-resolved fluid images from coarse data. Unlike the prior research to increase the resolution of coarse data artificially generated by simple bilinear down-sampling, our model that consists of a degradation neural network and a super-resolution neural network aims to learn the mappings between experimental low-resolution data and corresponding HR data. What is more, channel and spatial attention modules are also adopted in D-SRA to facilitate the restoration of abundant and critical details of flow fields. The proposed model is validated by two high-speed schlieren experiments of under-expanded impinging supersonic jets. The comprehensive capability of D-SRA is statistically analyzed based on the synthetic unpaired schlieren images. The spatial-resolution of coarse images can be successfully augmented by 4 2 times and 8 2 times with most physical details recovered perfectly, which outperforms the existing method. The D-SRA also exhibits considerable generalization and robustness against unknown-degenerated schlieren images. Moreover, the practicability of the proposed method is also further explored on real unpaired jets schlieren images. It is convincingly demonstrated that the present study successfully surpasses the performance limitations of high-speed cameras and has significant applications in various fluid experiments to obtain flow images with high spatial and temporal resolution. [ABSTRACT FROM AUTHOR]

This work presents an experimental study on the splashing behaviors of drops impinging on rough solid surfaces. Most prior studies have shown the increase in surface roughness can promote the occurrence of a drop splash. Interestingly, we found two opposite effects of surface roughness on the drop splash that the increase in surface roughness can promote splash of low-viscosity drops but suppress splash of high-viscosity drops. According to the wetting state of the spreading lamella on rough surfaces, the splash regime can be classified into two modes: corona splash and prompt splash. It is found that the increase in surface roughness can promote the prompt splash but suppress the corona splash. The increase in surface roughness could provide wide channels for air to escape and suppress the corona splash. Meanwhile, the larger surface roughness could also disrupt the expanding lamella and promote the prompt splash. The dimensionless parameter Ohr can be used to distinguish two splash regimes, and the critical value Ohrc is obtained from experimental results, at which the splash regime changes from the prompt to corona splash. Emphatically, we obtain the splash criteria in two regions, which could reflect the opposite effects of surface roughness on the drop splash and successfully characterize the splashing behaviors in this work and previous studies. The results of this work are expected to provide valuable insights to control the drop splash in industrial applications. [ABSTRACT FROM AUTHOR]

The dominant resonance mode switch pattern concerning nozzle pressure ratio and impinging distance for under-expanded jets issuing from a convergent nozzle and impacting a flat surface is demonstrated for the first time. Schlieren visualization and acoustic measurements have been carried out to simultaneously capture the dynamic and acoustic properties of impinging jets with a nozzle pressure ratio ranging from 2.00 to 4.30 (from moderately under-expanded to highly under-expanded) and an impingement distance extent 3.0D to 11.0D, where D is the nozzle exit diameter. Five bands within which symmetric mode predominates have been discovered. Jets within these bands also exhibit high amplitudes in overall sound pressure level. Besides, dominant frequencies within any band remain relatively stable when impinging distance is fixed, while a negative correlation between dominant frequencies and impingement distance has been found. Dynamic mode decomposition has been applied to schlieren snapshot sequences to achieve dimension reduction, by which the sound source location of tones can be determined. It is found that symmetric mode finds its genesis near the impingement surface, whereas the source related to asymmetric mode lies in the shear layer near the third shock cell or the standoff shock, depending on the number of shock cells between the nozzle exit and the impinging surface. This difference in acoustic feedback paths serves as the cause of the mode switch. Further, the symmetric mode's source location's stability results in the stability of dominant frequencies within a band when impinging distance is fixed. [ABSTRACT FROM AUTHOR]

Surface acoustic wave-based particle/bioparticle manipulation has emerged as a promising tool for disease diagnosis. The effects of the titled angle of the acoustic field θ and the microchannel aspect ratios β on the particle migration mode, the force of particle, and the three-dimensional focusing behavior are studied by using simulation and high-speed microscopic visualizations experiments. The acoustic field tilt range is from 0° to 15°, and the wavelength is 160 μm. Particle migration trajectory is observed from high-speed photographic images. Compared with most parallel acoustic fields, the particle migration efficiency of the tilted acoustic field is higher because the acoustic radiation force (Fr) continues to act on the particles in the lateral direction. The tilted angle of the acoustic field is not a fixed value (usually 15°), and there is an optimal angle to match the maximum lateral migration of the target particles. A model is put forward to predict the optimal acoustic field tilt-angle for acoustofluidic devices, which can achieve 96% separation of 15 μm target particles. The change in the direction of the Fr drives the particles to create two typical migration states during the lateral migration process, named continuous migration and intermittent migration. The phenomenon of multi-layer particle focus in the vertical Z-direction of the microchannel is experimentally observed for the first time, which mainly depends on whether the microchannel has enough height to make multiple acoustic pressure nodes in the vertical direction. Two or even three layers of particle focus lines can be observed in the vertical direction at the microchannel aspect ratios β > 0.5. The research results provide new insight into the high-throughput development of microfluidic devices. [ABSTRACT FROM AUTHOR]

In this paper, two types of stationary striations appearing in an argon helicon plasma source are presented. The formation and features of the striations were investigated experimentally under different conditions, including RF power, gas pressure, and external magnetic field. The results show that the striation spacing decreases as the gas pressure increases but does not change significantly along with the magnetic field and the RF power. It is suggested that these striations are strongly related to the non-local effect of electron kinetics in the plasma channel with a weak electric field. The different pressures in downstream and antenna regions will lead to different types of striations in an argon helicon plasma source. [ABSTRACT FROM AUTHOR]

The upstream-propagating waves of feedback loops in under-expanded impinging jets are investigated through several typical flow conditions. Schlieren image capturing and far-field acoustic measurement are applied to the jet. The flow structures related to the discrete tones are extracted through dynamic mode decomposition (DMD), and the standing waves formed by the resonance are identified from the normalized amplitude fields of the chosen DMD modes. Spatial Fourier transforms are applied along the axial direction on the chosen DMD modes to obtain the spatial wavenumber spectra, from which the two wave disturbances caused by the interaction between Kelvin–Helmholtz (K–H) waves and shock cells can be identified. The upstream and downstream-propagating components of the feedback loop are rebuilt, respectively, via bandpass filtering. The wavenumbers of the upstream-propagating components in the feedback loop and the wavenumbers of disturbance waves are compared along the jet shear layer; the results suggest more than one closure mechanism of the feedback loop. For the impinging tones which have the same frequencies as the A1 and B modes in free jet, the closure mechanism of the feedback loop is the Mach radiation generated by the interaction between K–H waves and shock cells. For the other tones, their frequencies are consistent well with the allowable frequency ranges of the neutral wave mode. The combination of the neutral wave mode with the classical feedback loop model also gives strong evidence that the upstream-propagating waves for these tones may be the jets' inherent neutral wave. [ABSTRACT FROM AUTHOR]

There are many practical applications of droplets freezing, and in many cases, it is necessary to prevent the droplets freezing to reduce the loss caused by freezing. Based on the many-body dissipative particle dynamics with energy conservation method, this research proposes an icing model that considers the recalescence process and initial ice mass fraction of droplets for the first time, which obtains a complete simulation of the two-phase four-stage freezing process of droplets. The accuracy and applicability of this model are verified by studying the single-phase Stefan problem, the recalescence process of droplet, and whether the initial ice mass fraction is considered for freezing. Then, the freezing process of droplets under four surface temperatures and five types of surface wettability was studied, and it was found that the temperature of droplets in recalescence stage would jump from nucleation temperature to equilibrium temperature, and almost unaffected by external factors. Change of the temperature distribution with dimensionless height H * before recalescence is only affected by the surface temperature and nucleation temperature. At the end of droplets recalescence, the initial ice mass fraction has little relationship with volume. As the contact angle, surface temperature, and droplet volume increase, temperature changes in the pre-cooling and solidification stages of droplets will slow down, and the solidification time will increase. Additionally, the temperature of the solid wall surface has almost no effect on the final ice shape, and the final ice tip phenomenon is more obvious on the surface with a larger contact angle. [ABSTRACT FROM AUTHOR]