Research on Track Fastener Service Status Detection Based on Improved Yolov4 Model

As an important part of railway lines, the healthy service status of track fasteners was very important to ensure the safety of trains. The application of deep learning algorithms was becoming an important method to realize its state detection. However, there was often a deficiency that the detection accuracy and calculation speed of model were difficult to balance, when the traditional deep learning model is used to detect the service state of track fasteners. Targeting this issue, an improved Yolov4 model for detecting the service status of track fasteners was proposed. Firstly, the Mixup data augmentation technology was introduced into Yolov4 model to enhance the generalization ability of model. Secondly, the MobileNet-V2 lightweight network was employed in lieu of the CSPDarknet53 network as the backbone, thereby reducing the number of algorithm parameters and improving the model’s computational efficiency. Finally, the SE attention mechanism was incorporated to boost the importance of rail fastener identification by emphasizing relevant image features, ensuring that the network’s focus was primarily on the fasteners being inspected. The algorithm achieved both high precision and high speed operation of the rail fastener service state detection, while realizing the lightweight of model. The experimental results revealed that, the MAP value of the rail fastener service state detection algorithm based on the improved Yolov4 model reaches 83.2%, which is 2.83% higher than that of the traditional Yolov4 model, and the calculation speed was improved by 67.39%. Compared with the traditional Yolov4 model, the proposed method achieved the collaborative optimization of detection accuracy and calculation speed.

Stimulated Raman scattering microscopy with phase-controlled light focusing and aberration correction for rapid and label-free, volumetric deep tissue imaging

We report a novel stimulated Raman scattering(SRS)microscopy technique featuring phase-controlled light focusing and aberration corrections for rapid,deep tissue 3D chemical imaging with subcellular resolution.To accomplish phasecontrolled SRS(PC-SRS),we utilize a single spatial light modulator to electronically tune the axial positioning of both the shortened-length Bessel pump and the focused Gaussian Stokes beams,enabling z-scanning-free optical sectioning in the sample.By incorporating Zernike polynomials into the phase patterns,we simultaneously correct the system aberrations at two separate wavelengths(~240 nm difference),achieving a~3-fold enhancement in signal-to-noise ratio over the uncorrected imaging system.PC-SRS provides>2-fold improvement in imaging depth in various samples(e.g.,polystyrene bead phantoms,porcine brain tissue)as well as achieves SRS 3D imaging speed of~13 Hz per volume for real-time monitoring of Brownian motion of polymer beads in water,superior to conventional point-scanning SRS 3D imaging.We further utilize PC-SRS to observe the metabolic activities of the entire tumor liver in living zebrafish in cellsilent region,unraveling the upregulated metabolism in liver tumor compared to normal liver.This work shows that PCSRS provides unprecedented insights into morpho-chemistry,metabolic and dynamic functioning of live cells and tissue in real-time at the subcellular level.

全身抗感染治疗下给予穿刺冲洗和切开引流两种术式治疗哺乳期乳腺脓肿的临床疗效观察

目的研究全身抗感染治疗下穿刺冲洗、切开引流治疗哺乳期乳腺脓肿的价值,为临床治疗提供必要指导.方法随机将2018年5月-2019年5月我院40例哺乳期乳腺脓肿患者分为实验组(20例,应用B超引导下穿刺冲洗治疗)、对照组(20例,应用切开引流治疗).对比两组患者各项临床指标.结果实验组术中出血量为(9.02±1.05)mL、脓腔愈合时间为(10.57±2.38)d、术后VAS评分为(1.67±0.55)分、瘢痕长度为(1.12±0.48)mm,均低于对照组,差异具备统计学研究意义(P<0.05).结论全身抗感染治疗条件下,哺乳期乳腺脓肿患者接受B超引导下穿刺冲洗治疗,疗效确切.

Theoretical Model of Dynamic Bulk Modulus for Aerated Hydraulic Fluid

Existing models of bulk modulus for aerated hydraulic fluids primarily focus on the effects of pressure and air fraction,whereas the effect of temperature on bulk modulus is disregarded.Based on the lumped parameter method and the full cavitation model,combined with the improved Henry’s law and the air polytropic course equation,a theoretical model of dynamic bulk modulus for an aerated hydraulic fluid is derived.The effects of system pressure,air fraction,and temperature on bulk modulus are investigated using the controlled variable method.The results show that the dynamic bulk modulus of the aerated hydraulic fluid is inconsistent during the compression process.At the same pressure point,the dynamic bulk modulus during expansion is higher than that during compression.Under the same initial air faction and pressure changing period,a higher temperature results in a lower dynamic bulk modulus.When the pressure is lower,the dynamic bulk modulus of each temperature point is more similar to each other.By comparing the theoretical results with the actual dynamic bulk modulus of the Shell Tellus S ISO32 standard air-containing oil,the goodness-of-fit between the theoretical model and experimental value at three temperatures is 0.9726,0.9732,and 0.9675,which validates the theoretical model.In this study,a calculation model of dynamic bulk modulus that considers temperature factors is proposed.It predicts the dynamic bulk modulus of aerated hydraulic fluids at different temperatures and provides a theoretical basis for improving the analytical model of bulk modulus.

An Ultrasonic Backscatter Instrument for Cancellous Bone Evaluation in Neonates

Ultrasonic backscatter technique has shown promise as a noninvasive cancellous bone assessment tool. A novel ultrasonic backscatter bone diagnostic （UBBD） instrument and an in vivo application for neonatal bone evaluation are introduced in this study. The UBBD provides several advantages, including noninvasiveness, non- ionizing radiation, portability, and simplicity. In this study, the backscatter signal could be measured within 5 s using the UBBD. Ultrasonic backscatter measurements were performed on 467 neonates （268 males and 199 females） at the left calcaneus. The backscatter signal was measured at a central frequency of 3.5 MHz. The delay （-/-1） and duration （7-2） of the backscatter signal of interest （SOl） were varied, and the apparent integrated backscatter （AIB）, frequency slope of apparent backscatter （FSAB）, zero frequency intercept of apparent backscatter （FIAB）, and spectral centroid shift （SCS） were calculated. The results showed that the SOl selection had a direct influence on cancellous bone evaluation. The AIB and FIAB were positively correlated with the gestational age （｜R｜ up to 0.45, P 〈 0.001） when -/-1 was short （〈 8 μS）, while negative correlations （｜R｜ up to 0.56, P 〈 0.001） were commonly observed for T1 〉 10 IJS. Moderate positive correlations （IRI up to 0.45, P 〈 0.001） were observed for FSAB and SCS with gestational age when 71 was long （〉 10 μs）. The 7-2 mainly introduced fluctuations in the observed correlation coefficients. The moderate correlations observed with UBBD demonstrate the feasibility of using the backscatter signal to evaluate neonatal bone status. This study also proposes an explicit standard for in vivo SOl selection and neonatal cancellous bone assessment.

Ultrasonic backscatter characterization of cancellous bone using a general Nakagami statistical model

The goal of this study is to analyze the statistics of the backscatter signal from bovine cancellous bone using a Nakagami model and to evaluate the feasibility of Nakagami-model parameters for cancellous bone characterization. Ultrasonic backscatter measurements were performed on 24 bovine cancellous bone specimens in vitro and the backscatter signals were compensated for the frequency-dependent attenuation prior to the envelope detection. The statistics of the backscatter envelope were modeled using the Nakagami distribution. Our results reveal that the backscatter envelope mainly followed pre-Rayleigh distributions, and the deviations of the backscatter envelope from Rayleigh distribution decreased with increasing bone density. The Nakagami shape parameter(i.e., m) was significantly correlated with bone densities(R = 0.78–0.81, p < 0.001) and trabecular microstructures(|R| = 0.46–0.78, p < 0.05). The scale parameter(i.e.,?) and signal-to-noise ratio(SNR) also yielded significant correlations with bone density and structural features. Multiple linear regressions showed that bone volume fraction(BV/TV) was the main predictor of the Nakagami parameters,and microstructure produced significantly independent contribution to the prediction of Nakagami distribution parameters,explaining an additional 10.2% of the variance at most. The in vitro study showed that statistical parameters derived with Nakagami model might be useful for cancellous bone characterization, and statistical analysis has potential for ultrasonic backscatter bone evaluation.

Recombinant adenovirus-mediated overexpression of 3β-hydroxysteroid-Δ24 reductase

3β-Hydroxysteroid-△24 reductase （DHCR24） is a multifunctional enzyme that localizes to the endoplasmic reticulum and has neuroprotective and cholesterol-synthesizing activities. DHCR24 overexpression confers neuroprotection against apoptosis caused by amyloid β deposition. The present study aimed to construct two recombinant adenoviruses driving DHCR24 expression specifically in neurons. Two SYN1 promoter DNA fragments were obtained from human （h） and rat （r）. Recombinant Ad-r（h）SYN1-DHCR24 was transfected into AD-293, N2A （mouse neuroblastoma）, and MIN6 （mouse pancreatic carcinoma） cells. Western blot analysis showed DHCR24 was specially expressed in 293 and N2A cells, but no specific band was found in MIN6 cells. This demonstrates that the recombinant adenoviruses successfully express DHCR24, and no expression is observed in non-neuronal cells. TUNEL assay results showed apoptosis was inhibited in adenovirus-transfected neurons. Detecting reactive oxygen species by immunoflu- orescence, we found that adenovirus transfection inhibits apoptosis through scavenging excess reactive oxygen species. Our findings show that the recombinant DHCR24 adenoviruses induce neuron-specific DHCR24 expression, and thereby lay the foundation for further studies on DHCR24 gene therapy for Alzheimer＇s disease.

High-resolution bone microstructure imaging based on ultrasonic frequency-domain full-waveform inversion

The main challenge in bone ultrasound imaging is the large acoustic impedance contrast and sound velocity differences between the bone and surrounding soft tissue. It is difficult for conventional pulse-echo modalities to give accurate ultrasound images for irregular bone boundaries and microstructures using uniform sound velocity assumption rather than getting a prior knowledge of sound speed. To overcome these limitations, this paper proposed a frequency-domain fullwaveform inversion(FDFWI) algorithm for bone quantitative imaging utilizing ultrasonic computed tomography(USCT).The forward model was calculated in the frequency domain by solving the full-wave equation. The inverse problem was solved iteratively from low to high discrete frequency components via minimizing a cost function between the modeled and measured data. A quasi-Newton method called the limited-memory Broyden–Fletcher–Goldfarb–Shanno algorithm(L-BFGS) was utilized in the optimization process. Then, bone images were obtained based on the estimation of the velocity and density. The performance of the proposed method was verified by numerical examples, from tubular bone phantom to single distal fibula model, and finally with a distal tibia-fibula pair model. Compared with the high-resolution peripheral quantitative computed tomography(HR-p QCT), the proposed FDFWI can also clearly and accurately presented the wavelength scaled pores and trabeculae in bone images. The results proved that the FDFWI is capable of reconstructing high-resolution ultrasound bone images with sub-millimeter resolution. The parametric bone images may have the potential for the diagnosis of bone disease.

Stimulated Raman scattering tomography for rapid three-dimensional chemical imaging of cells and tissue

Three-dimensional(3D)imaging is essential for understanding intricate biological and biomedical systems,yet live cell and tissue imaging applications still face challenges due to constrained imaging speed and strong scattering in turbid media.Here,we present a unique phase-modulated stimulated Raman scattering tomography(PM-SRST)technique to achieve rapid label-free 3D chemical imaging in cells and tissue.To accomplish PM-SRST,we utilize a spatial light modulator to electronically manipulate the focused Stokes beam along the needle Bessel pump beam for SRS tomography without the need for mechanical z scanning.We demonstrate the rapid 3D imaging capability of PM-SRST by real-time monitoring of 3D Brownian motion of polystyrene beads in water with 8.5 Hz volume rate,as well as the instant biochemical responses to acetic acid stimulants in MCF-7 cells.Further,combining the Bessel pump beam with a longer wavelength Stokes beam(NIR-II window)provides a superior scattering resilient ability in PM-SRST,enabling rapid tomography in deeper tissue areas.The PM-SRST technique providestwofold enhancement in imaging depth in highly scattering media(e.g.,polymer beads phantom and biotissue like porcine skin and brain tissue)compared with conventional point-scan SRS.We also demonstrate the rapid 3D imaging ability of PM-SRST by observing the dynamic diffusion and uptake processes of deuterium oxide molecules into plant roots.The rapid PM-SRST developed can be used to facilitate label-free 3D chemical imaging of metabolic activities and functional dynamic processes of drug delivery and therapeutics in live cells and tissue.

Deep learning analysis of smart meter data from a small sample of room air conditioners facilitates routine assessment of their operational efficiency

Room air conditioners (RACs) are crucial household appliances that consume substantial amounts of electricity. Their efficiency tends to deteriorate over time, resulting in unnecessary energy wastage. Smart meters have become popular to monitor electricity use of home appliances, offering underexplored opportunities to evaluate RAC operational efficiency. Traditional supervised data-driven analysis methods necessitate a large sample size of RACs and their efficiency, which can be challenging to acquire. Additionally, the prevalence of zero values when RACs are off can skew training. To overcome these challenges, we assembled a dataset comprising a limited number of window-type RACs with measured operational efficiencies from 2021. We devised an intuitive zero filter and resampling protocol to process smart meter data and increase training samples. A deep learning-based encoder–decoder model was developed to evaluate RAC efficiency. Our findings suggest that our protocol and model accurately classify and regress RAC operational efficiency. We verified the usefulness of our approach by evaluating the RACs replaced in 2022 using 2022 smart meter data. Our case study demonstrates that repairing or replacing an inefficient RAC can save electricity by up to 17 %. Overall, our study offers a potential energy conservation solution by leveraging smart meters for regularly assessing RAC operational efficiency and facilitating smart preventive maintenance.

Phase-modulated multi-foci microscopy for rapid 3D imaging

3D imaging technology is pivotal in monitoring the functional dynamics and morphological alterations in living cells and tissues.However,conventional volumetric imaging associated with mechanical z-scanning encounters challenges in limited 3D imaging speed with inertial artifact.Here,we present a unique phase-modulated multifoci microscopy (PM^(3)) technique to achieve snapshot 3D imaging with the advantages of extended imaging depths and adjustable imaging intervals between each focus in a rapid fashion.To accomplish the tasks,we utilize a spatial light modulator (SLM) to encode the phases of the scattered or fluorescence light emanating from a volumetric sample and then project the multiple-depth images of the sample onto a single charge-coupled device camera for rapid 3D imaging.We demonstrate that the PM^(3)technique provides~55-fold improvement in imaging depth in polystyrene beads phantom compared to the depth of field of the objective lens used.PM^(3)also enables the real-time monitoring of Brownian motion of fluorescent beads in water at a 15 Hz volume rate.By precisely manipulating the phase of scattered light on the SLM,PM^(3)can pinpoint the specific depth information in living zebrafish and rapidly observe the 3D dynamic processes of blood flow in the zebrafish trunk.This work shows that the PM^(3)technique developed is robust and versatile for fast 3D dynamic imaging in biological and biomedical systems.

Viral vectored vaccines:design,development,preventive and therapeutic applications in human diseases

Human diseases,particularly infectious diseases and cancers,pose unprecedented challenges to public health security and the global economy.The development and distribution of novel prophylactic and therapeutic vaccines are the prioritized countermeasures of human disease.Among all vaccine platforms,viral vector vaccines offer distinguished advantages and represent prominent choices for pathogens that have hampered control efforts based on conventional vaccine approaches.Currently,viral vector vaccines remain one of the best strategies for induction of robust humoral and cellular immunity against human diseases.Numerous viruses of different families and origins,including vesicular stomatitis virus,rabies virus,parainfluenza virus,measles virus,Newcastle disease virus,influenza virus,adenovirus and poxvirus,are deemed to be prominent viral vectors that differ in structural characteristics,design strategy,antigen presentation capability,immunogenicity and protective efficacy.This review summarized the overall profile of the design strategies,progress in advance and steps taken to address barriers to the deployment of these viral vector vaccines,simultaneously highlighting their potential for mucosal delivery,therapeutic application in cancer as well as other key aspects concerning the rational application of these viral vector vaccines.Appropriate and accurate technological advances in viral vector vaccines would consolidate their position as a leading approach to accelerate breakthroughs in novel vaccines and facilitate a rapid response to public health emergencies.

Extremely low friction on gold surface with surfactant molecules induced by surface potential

An extremely low friction state was observed on the gold surface induced by applying a specific negative potential in cationic surfactant solution.The friction force showed a remarkable reduction from 8.3 to 3.5×10−2 nN(reduced by 99.6%)with increasing the period of negative applied potential,and the final friction coefficient could reduce down to 3×10−4.The extremely low friction state was robust,and it also exhibited an excellent load bearing capacity,which cannot be damaged by a high load.Moreover,the extremely low friction state achieved under negative applied potential could keep stable even after the removal of potential,but failed in a short time,once a specific positive potential was applied.It was demonstrated that there was a stable electro-adsorption of surfactant molecules on the gold surface induced by applying a negative potential,leading to the formation of a bilayer structure on the gold surface.The hydration layers of the bilayer on the gold surface and micelles on the silica probe provided a shear plane with an extremely low shear strength,leading to the extremely low friction state on the gold surface.This study provides a method to achieve extremely low friction state by applied potential.

Single-cell RNA-Seq reveals transcriptional regulatory networks directing the development of mouse maxillary prominence

During vertebrate embryonic development,neural crest-derived ectomesenchyme within the maxillary prominences undergoes precisely coordinated proliferation and differentiation to give rise to diverse craniofacial structures,such as tooth and palate.However,the transcriptional regulatory networks underpinning such an intricate process have not been fully elucidated.Here,we perform single-cell RNA-Seq to comprehensively characterize the transcriptional dynamics during mouse maxillary development from embryonic day(E)10.5eE14.5.Our single-cell transcriptome atlas of~28,000 cells uncovers mesenchymal cell populations representing distinct differentiating states and reveals their developmental trajectory,suggesting that the segregation of dental from the palatal mesenchyme occurs at E11.5.Moreover,we identify a series of key transcription factors(TFs)associated with mesenchymal fate transitions and deduce the gene regulatory networks directed by these TFs.Collectively,our study provides important resources and insights for achieving a systems-level understanding of craniofacial morphogenesis and abnormality.

3D DEM simulation of hard rock fracture in deep tunnel excavation induced by changes in principal stress magnitude and orientation

To achieve the loading of the stress path of hard rock,the spherical discrete element model(DEM)and the new flexible membrane technology were utilized to realize the transient loading of three principal stresses with arbitrary magnitudes and orientations.Furthermore,based on the deep tunnel of China Jinping Underground Laboratory II(CJPL-II),the deformation and fracture evolution characteristics of deep hard rock induced by excavation stress path were analyzed,and the mechanisms of transient loading-unloading and stress rotation-induced fractures were revealed from a mesoscopic perspective.The results indicated that the stressestrain curve exhibits different trends and degrees of sudden changes when subjected to transient changes in principal stress,accompanied by sudden changes in strain rate.Stress rotation induces spatially directional deformation,resulting in fractures of different degrees and orientations,and increasing the degree of deformation anisotropy.The correlation between the degree of induced fracture and the unloading magnitude of minimum principal stress,as well as its initial level is significant and positive.The process of mechanical response during transient unloading exhibits clear nonlinearity and directivity.After transient unloading,both the minimum principal stress and minimum principal strain rate decrease sharply and then tend to stabilize.This occurs from the edge to the interior and from the direction of the minimum principal stress to the direction of the maximum principal stress on theε1-ε3 plane.Transient unloading will induce a tensile stress wave.The ability to induce fractures due to changes in principal stress magnitude,orientation and rotation paths gradually increases.The analysis indicates a positive correlation between the abrupt change amplitude of strain rate and the maximum unloading magnitude,which is determined by the magnitude and rotation of principal stress.A high tensile strain rate is more likely to induce fractures under low minimum principal stress.

喀斯特洞穴滴水细菌群落组成及其代谢功能的季节性变化

洞穴是研究地下生物圈的天然实验室,而滴水是连接洞穴内部和外部环境的桥梁,对滴水微生物群落结构以及代谢功能进行研究,可以为洞穴中微生物组成、来源以及微生物驱动的元素循环提供重要信息.本研究采用Illumina Miseq平台的16S rRNA二代测序技术及Biolog-ECO微平板检测法,对湖北和尚洞弱光带滴水中的细菌群落多样性、细菌群落代谢功能多样性以及环境因子进行了为期2年的动态监测.结果表明:洞穴滴水中优势细菌属为不动杆菌属(Acinetobacter)和假单胞菌属(Pseudomonas)并表现出明显的季节性变化,不动杆菌属(Acinetobacter)相对丰度在夏季最高、冬季最低,而假单胞菌属(Pseudomonas)相对丰度的季节性变化正好相反;这种季节性差异与宜昌地区的月平均降水量紧密相关.同时,基于16SrRNA的PICRUSt代谢功能预测及Biolog-ECO微平板法均显示洞穴滴水中细菌群落代谢功能具有季节性变化,并且这种代谢能力的季节性变化与不动杆菌属(Acinetobacter)相对丰度的季节性变化显著正相关.总之,湖北宜昌和尚洞弱光区滴水中的细菌群落结构的季节性变化与降水量密切相关,同时优势类群不动杆菌属(Acinetobacter)是滴水代谢能力的主要贡献者.此研究将环境因子、滴水细菌群落组成及群落代谢能力三者紧密结合起来,为进一步解译洞穴这一特殊的地下生态系统中微生物群落组成及其代谢特征的变化规律奠定了基础.

Chimeric Newcastle Disease Virus-like Particles Containing DC-Binding Peptide-Fused Haemagglutinin Protect Chickens from Virulent Newcastle Disease Virus and H9N2 Avian Influenza Virus Challenge

Newcastle disease virus(NDV)and H9N2 subtype Avian influenza virus(AIV)are two notorious avian respiratory pathogens that cause great losses in the poultry industry.Current inactivated commercial vaccines against NDV and AIV have the disadvantages of inadequate mucosal responses,while an attenuated live vaccine bears the risk of mutation.Dendritic cell(DC)targeting strategies are attractive for their potent mucosal and adaptive immune-stimulating ability against respiratory pathogens.In this study,DC-binding peptide(DCpep)-decorated chimeric virus-like particles(cVLPs),containing NDV haemagglutinin–neuraminidase(HN)and AIV haemagglutinin(HA),were developed as a DC-targeting mucosal vaccine candidate.DCpep-decorated cVLPs activated DCs in vitro,and induced potent immune stimulation in chickens,with enhanced secretory immunoglobulin A(sIgA)secretion and splenic T cell differentiation.40μg cVLPs can provide full protection against the challenge with homologous,heterologous NDV strains,and AIV H9N2.In addition,DCpep-decorated cVLPs could induce a better immune response when administered intranasally than intramuscularly,as indicated by robust s IgA secretion and a reduced virus shedding period.Taken together,this chimericVLPs are a promising vaccine candidate to control NDV and AIV H9N2 and a useful platform bearing multivalent antigens.

Crack evolution of soft–hard composite layered rock-like specimens with two fissures under uniaxial compression

Acoustic emission and digital image correlation were used to study the spatiotemporal evolution characteristics of crack extension of soft and hard composite laminated rock masses(SHCLRM)containing double fissures under uniaxial compression.The effects of different rock combination methods and prefabricated fissures with different orientations on mechanical properties and crack coalescence patterns were analyzed.The characteristics of the acoustic emission source location distribution,and frequency changes of the crack evolution process were also investigated.The test results show that the damage mode of SHCLRM is related to the combination mode of rock layers and the orientation of fractures.Hard layers predominantly produce tensile cracks;soft layers produce shear cracks.The first crack always sprouts at the tip or middle of prefabricated fractures in hard layers.The acoustic emission signal of SHCLRM with double fractures has clear stage characteristics,and the state of crack development can be inferred from this signal to provide early warning for rock fracture instability.This study can provide a reference for the assessment of the fracture development status between adjacent roadways in SHCLRM in underground mines,as well as in roadway layout and support.

Urban Stormwater Modeling with Local Inertial Approximation Form of Shallow Water Equations: A Comparative Study

This study focused on the performance and limitations of the local inertial approximation form model(LIM)of the shallow water equations(SWEs)when applied in urban flood modeling.A numerical scheme of the LIM equations was created using finite volume method with a first-order spatiotemporal Roe Riemann solver.A simplified urban stormwater model(SUSM)considering surface and underground dual drainage system was constructed based on LIM and the US Environmental Protection Agency Storm Water Management Model.Moreover,a complete urban stormwater model(USM)based on the SWEs with the same solution algorithm was used as the evaluation benchmark.Numerical results of the SUSM and USM in a highly urbanized area under four rainfall return periods were analyzed and compared.The results reveal that the performance of the SUSM is highly consistent with that of the USM but with an improvement in computational efficiency of approximately 140%.In terms of the accuracy of the model,the SUSM slightly underestimates the water depth and velocity and is less accurate when dealing with supercritical flow in urban stormwater flood modeling.Overall,the SUSM can produce comparable results to USM with higher computational efficiency,which provides a simplified and alternative method for urban flood modeling.

Three-dimensional ultrasound subwavelength arbitrary focusing with broadband sparse metalens

Ultrasound focusing in three-dimensional(3 D)space is of crucial and enduring significance in a variety of biomedical and industrial applications.Conventional ultrasound focusing based on active phase array or passive geometry of bulky size is unable to realize the 3 D arbitrary focusing with subwavelength resolution.Acoustic metamaterial of complex deep-subwavelength microstructure has facilitated the advanced airborne-sound-focusing but is inevitably not applicable for underwater ultrasound,restricted by the law between the multi-modes coupling/thermal viscosity and the feature size of the structure.Here,we aim to circumvent the restriction by increasing the feature size of the metamaterial while keeping the compact overall geometry,and realize the robust subwavelength ultrasound focusing with the sparse metalens of the wavelength-scale meta-atom.We theoretically propose and demonstrate numerically and experimentally the broadband arbitrary ultrasound focusing in 3 D space.The axial and off-axis ultrasound focusing with the subwavelength resolution(FWHM<0.58λ)are achieved by the spatially sparse and compact metalens within one-octave bandwidth.With advantages of 3 D freewheeling focusing,subwavelength resolution,spatial sparsity,geometric simplicity,and broadband,the sparse metalens would offer more initiatives to advanced researches in ultrasound focusing and empower applications such as precise biomedical imaging and therapy,nondestructive evaluation,integrated and multiplexed ultrasound devices.