Acta Mechanica Sinica最新文献

{"title":"Mechanisms of plasma actuation on hypersonic boundary-layer instability and mode evolution","authors":"Zhehao Li \u0000 (,&nbsp;),&nbsp;Caihong Su \u0000 (,&nbsp;),&nbsp;Hesen Yang \u0000 (,&nbsp;),&nbsp;Hua Liang \u0000 (,&nbsp;)","doi":"10.1007/s10409-026-25802-x","DOIUrl":"10.1007/s10409-026-25802-x","url":null,"abstract":"<div><p>Plasma-based control of hypersonic boundary layer transition has garnered considerable attention, yet its underlying mechanisms remain poorly understood. This study investigates the effects of plasma generated by surface arc discharge (SAD) actuators on a Mach 6 flat plate boundary layer, focusing on the evolution of instability modes. The SAD actuators are modeled as localized cylindrical heat sources, and their effects are analyzed using direct numerical simulation (DNS) and linear stability theory (LST). The results demonstrate that plasma-induced disturbances significantly modify the mean flow, altering the characteristics of instability modes. DNS confirms that small disturbances evolve linearly within plasma-modified flows. Notably, the second mode is suppressed, while the first mode is significantly amplified, consistent with LST predictions. This amplification of low-frequency disturbances may explain the experimentally observed promotion of transition by plasma, as these disturbances are known to dominate the transitional stage. Furthermore, while excitation frequency examined in this study has minimal impact on the amplitude evolution of instability modes, increased plasma energy substantially enhances disturbance energy, potentially accelerating the onset of transition.</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"42 11","pages":""},"PeriodicalIF":4.0,"publicationDate":"2026-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148613942","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Enhanced lumped parameter modeling of seated humans for coupling vibration response analysis","authors":"Wei Ding \u0000 (,&nbsp;),&nbsp;Leizhi Wang \u0000 (,&nbsp;),&nbsp;Zhaobo Chen \u0000 (,&nbsp;),&nbsp;Hongrui Ao \u0000 (,&nbsp;),&nbsp;Hui Yan \u0000 (,&nbsp;),&nbsp;Zhitong Li \u0000 (,&nbsp;)","doi":"10.1007/s10409-026-25407-x","DOIUrl":"10.1007/s10409-026-25407-x","url":null,"abstract":"<div><p>During vehicle operation, road-induced vertical vibrations excite coupled whole-body dynamic responses in occupants, resulting in ergonomic concerns such as motion-induced fatigue and diminished comfort. This study develops lumped parameter models with multiple degrees of freedom to systematically investigate the formation mechanism of coupling responses in seated humans under vertical excitation, thereby overcoming the limitations of conventional single-axis models. Three stiffness and damping distribution patterns (Models A, B, and C) are proposed based on biomechanical characteristics. Parameter identification demonstrates that the linear dynamic properties of the torso (Model B) predominantly govern the frequency-domain characteristics of the coupling response. Moreover, an enhanced model (Model D) is introduced, for the first time, to quantitatively analyze the effect of a natural forward-leaning posture (head <i>α</i>₁=9.0°, upper torso <i>α</i>₂=15.1°) on coupling vibrations in a seated position. Frequency-domain analysis indicates that the human body exhibits globally coordinated motion below 3.5 Hz, whereas local organ resonances prevail above 6 Hz. Simulations reveal that a 15° backrest support angle can reduce fore-and-aft seat-to-head transmissibility by 87.2% without impairing vertical vibration reduction. This study offers theoretical insights and design principles for vibration suppression in vehicle seat systems, contributing substantially to the enhancement of ride comfort and occupant health protection.</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"42 10","pages":""},"PeriodicalIF":4.0,"publicationDate":"2026-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148613645","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Study on vibration reduction mechanism of nonlinear energy sink containing dry friction damping","authors":"Chenyang Zhang \u0000 (,&nbsp;),&nbsp;Xianghong Li \u0000 (,&nbsp;),&nbsp;Yongjun Shen \u0000 (,&nbsp;)","doi":"10.1007/s10409-026-25348-x","DOIUrl":"10.1007/s10409-026-25348-x","url":null,"abstract":"<div><p>Nonlinear energy sinks containing dry friction damping (DNES) hold significant potential in vibration control. To unveil DNES’s underlying mechanism and explore the vibration reduction effect, this study couples DNES with a typical Duffing system having quintic nonlinear stiffness under periodic excitations. Initially, the coupled DNES system’s dynamic model is formulated based on Newton’s laws. Subsequently, the system’s bifurcation behavior is examined using bifurcation theory and fast-slow analysis. Numerical simulations determine equilibrium points, thus clarifying the vibration reduction mechanism. Upon coupling DNES, the system experiences a Fold bifurcation marked by a rapid transition, where the motion trajectory is transformed from a large amplitude and high frequency vibration to a bursting oscillation of spiking state and quiescent state. This phenomenon occurs because the unstable equilibrium point stabilizes after DNES coupling, enhancing its attraction to the motion trajectory. Moreover, observations show that DNES vibration has a smaller amplitude than NES vibration, improving the vibration reduction effect’s stability. DNES exhibits a favorable vibration reduction effect, maintaining it even when the external excitation intensity increases.</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"42 10","pages":""},"PeriodicalIF":4.0,"publicationDate":"2026-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148613570","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A hardware-algorithm co-designed framework for HDR imaging and dehazing in extreme rocket launch environments","authors":"Jing Tao \u0000 (,&nbsp;),&nbsp;Banglei Guan \u0000 (,&nbsp;),&nbsp;Pengju Sun \u0000 (,&nbsp;),&nbsp;Taihang Lei \u0000 (,&nbsp;),&nbsp;Yang Shang \u0000 (,&nbsp;),&nbsp;Qifeng Yu \u0000 (,&nbsp;)","doi":"10.1007/s10409-026-25875-x","DOIUrl":"10.1007/s10409-026-25875-x","url":null,"abstract":"<div><p>Quantitative optical measurement of critical mechanical parameters—such as plume flow fields, shock wave structures, and nozzle oscillations—during rocket launch faces severe challenges due to extreme imaging conditions. Intense combustion creates dense particulate haze and luminance variations exceeding 120 dB, degrading image data and undermining subsequent photogrammetric and velocimetric analyses. To address these issues, we propose a hardware-algorithm co-design framework that combines a custom spatially varying exposure (SVE) sensor with a physics-aware dehazing algorithm. The SVE sensor acquires multi-exposure data in a single shot, enabling robust haze assessment without relying on idealized atmospheric models. Our approach dynamically estimates haze density, performs region-adaptive illumination optimization, and applies multi-scale entropy-constrained fusion to effectively separate haze from scene radiance. Validated on real launch imagery and controlled experiments, the framework demonstrates superior performance in recovering physically accurate visual information of the plume and engine region. This offers a reliable image basis for extracting key mechanical parameters, including particle velocity, flow instability frequency, and structural vibration, thereby supporting precise quantitative analysis in extreme aerospace environments.</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"42 10","pages":""},"PeriodicalIF":4.0,"publicationDate":"2026-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148613189","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Parameter identification of the viscoelastic constitutive model for particle filled polymer composites based on physics-informed neural operator","authors":"Xueren Wang \u0000 (,&nbsp;),&nbsp;Taotao Zhang \u0000 (,&nbsp;),&nbsp;Yuqiang Yang \u0000 (,&nbsp;),&nbsp;Jiming Cheng \u0000 (,&nbsp;),&nbsp;Lihua Wen \u0000 (,&nbsp;),&nbsp;Ming Lei \u0000 (,&nbsp;),&nbsp;Xiao Hou \u0000 (,&nbsp;)","doi":"10.1007/s10409-026-25882-x","DOIUrl":"10.1007/s10409-026-25882-x","url":null,"abstract":"<div><p>The time-/temperature-dependent viscoelasticity behaviors in polymer composites are due to the memory decay effects, inducing various interesting phenomena, including the shape memory effects, the morphology evolution in living of organisms, temperature-dependent fracture behaviors, and so forth. To model those behaviors, various constitutive models based convolutional integrals have been developed for capturing viscoelasticity. However, the more refined model introduced a greater number of parameters and made the parameter identification more intricate, hardening their applications. To solve this problem, we developed a viscoelastic constitutive artificial neural network (VCANN) for automated parameter identification. Following the recently developed physics-informed neural operator, the activation functions of the network architecture were chosen to incorporate the physical knowledge in the standard viscoelastic model within the continuum mechanics framework. This VCANN is equivalent to the viscoelastic model, mapping the input variables (time, temperature, and deformation histories) to the stress responses, and the network node weights are equivalent to the model parameters. Therefore, the parameter identification problems are equivalently transformed into the training problem of the VCANN. To validate the parameter identification by this VCANN, we used the finite element (FE) simulation method to generate datasets of the mechanical responses in polymer composites under different strain states (uniaxial tension and equibiaxial tension) and different loading history (monotonic stretching, relaxation, and step loading). Six training scenarios indicate that as the dataset incorporates more diverse material deformation features, the parameters identified by VCANN become more precise. The datasets should include both uniaxial and biaxial tensile data to achieve the decoupled identification of bulk modulus and shear modulus. Overall, this developed method could reduce the application threshold of the viscoelastic constitutive model by establishing a bridge between the results of experiments and the input of parameters in FE simulations.</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"42 11","pages":""},"PeriodicalIF":4.0,"publicationDate":"2026-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148466498","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Turbulent/non-turbulent interface identification using Poisson reconstruction","authors":"Chuangxin He \u0000 (,&nbsp;),&nbsp;Yuyao Zhang \u0000 (,&nbsp;),&nbsp;Yingzheng Liu \u0000 (,&nbsp;)","doi":"10.1007/s10409-026-25830-x","DOIUrl":"10.1007/s10409-026-25830-x","url":null,"abstract":"<div><p>This study introduces a novel methodology for identifying the turbulent/non-turbulent interface (TNTI) in turbulent flows using Poisson surface reconstruction. Traditional TNTI detection methods based on vorticity thresholding often either result in multi-layered isosurfaces or fail to accurately capture engulfment structures. By first generating a point cloud from vorticity-based threshold points and subsequently applying Poisson reconstruction, a smooth, single-layer, watertight surface is obtained that faithfully represents both the outer envelope and internal engulfment features of the TNTI. The method is applied to a large-eddy simulation of a separated and reattaching turbulent boundary layer behind a wall-mounted rib. Results demonstrate significant improvements in capturing the intricate topology of the TNTI, enabling detailed analysis of entrainment mechanisms. Statistical evaluations of interface height and entrainment rate reveal distinct flow regimes influenced by separation and reattachment, highlighting the efficacy of the proposed approach in advancing the understanding of turbulent interfacial dynamics.</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"42 10","pages":""},"PeriodicalIF":4.0,"publicationDate":"2026-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148466487","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A multilayer bi-directional composite corrugated structure with excellent penetration resistance based on ballistic deflection","authors":"Hao Han \u0000 (,&nbsp;),&nbsp;Jin-Shui Yang \u0000 (,&nbsp;),&nbsp;Shun-Yu Yao \u0000 (,&nbsp;),&nbsp;Yao-Yao Xu \u0000 (,&nbsp;),&nbsp;Xu-Chang Liu \u0000 (,&nbsp;)","doi":"10.1007/s10409-026-51093-x","DOIUrl":"10.1007/s10409-026-51093-x","url":null,"abstract":"<div><p>To address the limitations of conventional structures in penetration resistance and deflection-based protection, based on the composite armor theory, we designed and fabricated a multilayer bi-directional composite corrugated structure with both anti-penetration and projectile deflection capabilities, and studied the effect of foam filling. A combined experimental and numerical approach was employed to systematically analyze the dynamic response of the structure under ballistic impacts at various positions and velocities. Key aspects such as ballistic limit, failure modes, deflection mechanisms, and energy absorption characteristics were investigated. Results showed that the ballistic resistance of the structure was significantly influenced by impact location, and the gradient thickness design effectively enhanced the deflection effect, increasing the maximum projectile deflection angle by up to 63.72%. Furthermore, compared to the unfilled configuration, foam filling improved the ballistic limit by up to 47.11%, enhanced energy absorption, mitigated structural damage, and increased the maximum deflection angle of the projectile, which exhibited a non-monotonic trend of first increasing and then decreasing with velocity.</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"42 11","pages":""},"PeriodicalIF":4.0,"publicationDate":"2026-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148466577","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Response minimization of MDOF nonlinear system driven by fGn","authors":"Qiangfeng Lü \u0000 (,&nbsp;),&nbsp;Weiqiu Zhu \u0000 (,&nbsp;),&nbsp;Maolin Deng \u0000 (,&nbsp;)","doi":"10.1007/s10409-026-51100-x","DOIUrl":"10.1007/s10409-026-51100-x","url":null,"abstract":"<div><p>Stochastic optimal control studies the Markov control of Markov diffusion process. For a system driven by the fractional Gaussian noise (fGn), the system response is non-Markov process. Thus, stochastic optimal control methods cannot be directly applied to stochastic optimal control of multi-degree-of-freedom (MDOF) nonlinear system driven by fGn. In the present paper, it is pointed out that fGn can be approximated to wideband noise under certain condition and the stochastic optimal control method based on the stochastic averaging method (SAM) of quasi-Hamiltonian system driven by wideband noise and dynamical programming can then be applied. The study in the present paper focuses on minimizing the response of MDOF nonlinear systems driven by fGn. Firstly, a controlled and fGn-driven quasi integrable Hamiltonian system is considered. Under certain conditions, the SAM of quasi-Hamiltonian systems driven by wideband noise is applied to obtain the partially-averaged and controlled Itô stochastic differential equations (SDEs). Then, applying the dynamical programming principle to the partially-averaged and controlled Itô SDEs yields the Hamilton-Jacobi-Bellman (HJB) equation. Solving HJB equation yields the optimal control force. Substitute the obtained optimal control force into the partially-averaged and controlled Itô SDEs and complete averaging to obtain completely averaged and optimal controlled Itô SDEs. Finally, solve the associated reduced Fokker-Planck-Kolmogorov (FPK) equation to obtain the response of the optimal controlled system. The proposed method is verified by comparing the theoretical results with those from Monte Carlo simulation.</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"42 11","pages":""},"PeriodicalIF":4.0,"publicationDate":"2026-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148466486","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The segmented propulsion characteristics of a start-up large-swing-angle supersonic split line nozzle and its convenient expressions","authors":"Shuhui Zhao \u0000 (,&nbsp;),&nbsp;Ben Guan \u0000 (,&nbsp;),&nbsp;Ge Wang \u0000 (,&nbsp;),&nbsp;Xisheng Luo \u0000 (,&nbsp;)","doi":"10.1007/s10409-026-51036-x","DOIUrl":"10.1007/s10409-026-51036-x","url":null,"abstract":"<div><p>The propulsion characteristics of a start-up large-swing-angle supersonic split line (SSSL) nozzle are numerically investigated. Focus is on the interpretations of its segmented thrust vectoring mechanisms and expressions using convenient theoretical methods. Within a nozzle pressure ratio (NPR) range of from 2.008 to 8.950, the present large-swing-angle SSSL nozzle typically exhibits three exhaust flow patterns and two operating modes. Correspondingly, the ensuing segmented vectoring performance is analyzed, and the underlying mechanisms are demonstrated. It is found that, despite the flow pattern variations in its two operating modes, a monotonic and segmented approximately linear dependency of the nozzle lateral thrust performance on NPR is generated. In calculating the nozzle mass flow rate, accurate results can be provided by applying the one-dimensional supersonic nozzle flow theory only if the effective throat area is well estimated. In formulating the nozzle lateral thrust, modified supersonic nozzle flow theories also demonstrate their potential. But in formulating the nozzle axial thrust, a convergent nozzle flow theory needs to be applied due to the present nozzle flow characteristics. These formulations provide preliminary and convenient thrust expressions for practical use.</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"42 11","pages":""},"PeriodicalIF":4.0,"publicationDate":"2026-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148466173","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"High-order optimization of quasi-zero stiffness energy harvesting vibration isolator","authors":"Jiayi Liu \u0000 (,&nbsp;),&nbsp;Tao Yang \u0000 (,&nbsp;),&nbsp;Yingxuan Cui \u0000 (,&nbsp;),&nbsp;Qingjie Cao \u0000 (,&nbsp;),&nbsp;Hongchun Luo \u0000 (,&nbsp;),&nbsp;Jupeng Fang \u0000 (,&nbsp;),&nbsp;Yongshou Liu \u0000 (,&nbsp;)","doi":"10.1007/s10409-026-51055-x","DOIUrl":"10.1007/s10409-026-51055-x","url":null,"abstract":"<div><p>The performance of traditional quasi-zero stiffness (QZS) systems in ultra-low frequency vibration isolation and energy harvesting is limited by constraints in achieving further stiffness reduction. The construction of high-order quasi-zero stiffness (HQZS) structures is a viable path to break through these barriers. Nevertheless, current HQZS implementations are limited in number, typically configuration-dependent, and difficult to design and extend. This paper highlights the essential role of high-order optimization in further reducing equivalent stiffness and proposes a coefficient compensation approach by focusing on Taylor expansion coefficients of the restoring force. This methodology pioneers a new design paradigm through the strategic combination of structures. A bio-inspired negative stiffness structure is designed to upgrade a conventional three-spring QZS system into a 9th-order QZS system. Theoretical, simulation, and experimental results demonstrate that high-order optimization significantly reduces the equivalent stiffness of the energy harvesting vibration isolator, leading to greatly enhanced performance in both ultra-low frequency vibration isolation and energy harvesting under harmonic and random excitations. This study offers valuable insights for designing high-order QZS systems and inspires new ideas for ultra-low frequency vibration control and energy harvesting technology.</p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":7109,"journal":{"name":"Acta Mechanica Sinica","volume":"42 11","pages":""},"PeriodicalIF":4.0,"publicationDate":"2026-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148466172","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}