An improved dynamic model for a silicone material beam with large deformation

Dynamic modeling for incompressible hyperelastic materials with large deformation is an important issue in biomimetic applications. The previously proposed lower-order fully parameterized absolute nodal coordinate formulation（ANCF） beam element employs cubic interpolation in the longitudinal direction and linear interpolation in the transverse direction, whereas it cannot accurately describe the large bending deformation. On this account, a novel modeling method for studying the dynamic behavior of nonlinear materials is proposed in this paper. In this formulation, a higher-order beam element characterized by quadratic interpolation in the transverse directions is used in this investigation. Based on the Yeoh model and volumetric energy penalty function, the nonlinear elastic force matrices are derived within the ANCF framework. The feasibility and availability of the Yeoh model are verified through static experiment of nonlinear incompressible materials. Furthermore,dynamic simulation of a silicone cantilever beam under the gravity force is implemented to validate the superiority of the higher-order beam element. The simulation results obtained based on the Yeoh model by employing three different ANCF beam elements are compared with the result achieved from a commercial finite element package as the reference result. It is found that the results acquired utilizing a higher-order beam element are in good agreement with the reference results,while the results obtained using a lower-order beam element are different from the reference results. In addition, the stiffening problem caused by volumetric locking can be resolved effectively by applying a higher-order beam element. It is concluded that the proposed higher-order beam element formulation has satisfying accuracy in simulating dynamic motion process of the silicone beam.

Application of Modelica/MWorks on modeling,simulation and optimization for electro-hydraulic servo valve system

Electro-hydraulic servo valve is a typical complicated multi-domain system constituted by mechanical, electric, hydraulic and magnetic components, which is widely used in electro-hydraulic servo systems such as construction machinery, heavy equipment, weapon and so forth. The traditional method of modeling and simulation of servo valve is based on block diagram or signal flow, which cannot describe the servo valve system from components level nor be used in modeling and simulation of overall servo systems. In the procedure of traditional method, computational causality must be involved in modeling of servo valve, which is inconvenient to execute modification on components or parameters. Modelica is an object-oriented modeling language which is suited for large, complex, heterogeneous and multi-domain systems. The key features of Modelica are multi-domain, object-oriented and non-causal, which are suitable for modeling of servo valve and make the model readable, reusable, and easy to modify. The simulation results show similar curves with traditional method. This new servo valve modeling and simulation method can provide the engineers a more efficient way to design and optimize a servo valve and an overall servo system.

Nonlinear dynamic analysis on rigid-flexible coupling system of an elastic beam

Previous work examined the effect of the attached stiffness matrix terms on stability of an elastic beam undergoing prescribed large overall motion. The aim of the present work is to extend the nonlinear formulations to an elastic beam with free large overall motion. Based on initial stress method, the nonlinear coupling equations of elastic beams are obtained with free large overall motion and the attached stiffness matrix is derived by solving sub-static formulation. The angular velocity and the tip deformation of the elastic pendulum are calculated. The analytical results show that the simulation results of the present model are tabled and coincide with the one-order approximate model. It is shown that the simulation results accord with energy conservation principle.

A Novel Perspective on Histopathology Provides Novel Insights into Surgical Effects in Pulmonary Atresia,Ventricular Septal Defect,and Major Aortopulmonary Collateral Arteries:A Case-Series Study

Background:Never had literatures characterized the relationship between the property of major aortopulmonary collateral arteries(MAPCAs)and outcomes of selective unifocalization of pulmonary atresia with ventricular septal defects and MAPCAs.Methods:This is a case-series study.Thirteen patients were included.Angiographybased assessment was conducted to determine whether collateral arteries should be unifocalized or treated with intraoperative ligature.Specimens were collected and stained by HE and ET+VG.Results:Twelve patients underwent one-stage unifocalization at a median age of 37 months(range:6–228 months)and a median weight of 14.0 kg(range:5.0–49.0 kg),which produced a favorable right ventricle to aortic systolic pressure ratio of no more than 0.5 except in one patient who died.Patients were divided into three groups:Group 1(n=6),had no native pulmonary arteries,and collateral arteries supplied all pulmonary blood;Group 2(n=6)presented dysplastic native pulmonary arteries on one or both sides,and in some lung lobes or segments,blood was supplied only by collateral arteries;Group 3(n=1)had well-developed left and right pulmonary arteries,and collateral arteries,and pulmonary arteries provided blood flow to the same segments.Pathological reports demonstrated two types of collateral arteries:Elastic arteries presented an arborization distribution similar to native pulmonary artery walls,while muscular arteries showed high resistance and distortion.We selectively unifocalized single-supply collateral arteries with morphologic features based on the arborization distribution.Conclusions:We found that there were two kinds of MAPCAs with different histology,and we performed selective UF for MAPCAs that might belong to the elastic artery.Selective unifocalization achieved a low right ventricle to aortic systolic pressure ratio and favorable surgical effects.

A rational design of bimetallic PdAu nanoflowers as efficient catalysts for methanol oxidation reaction

Methanol fuel cells have been intensively developed as clean and high-efficiency energy conversion system due to their high efficiency and low emission of pollutants.Here,we developed a simple aqueous synthetic method to prepare bimetallic PdAu nanoflowers catalysts for methanol oxidation reaction(MOR)in alkaline environment.Their composition can be directly tuned by changing the ratio between Pd and Au precursors.Compared with commercial Pd/C catalyst,all of the PdAu nanoflowers catalysts show the enhanced catalytic activity and durability.In particular,the PdAu nanoflowers specific activity reached 0.72 mA/cm^(2),which is 14 times that of commercial Pd/C catalyst.The superior MOR activity could be attributed to the unique porous structure and the shift of the d-band center of Pd.

Contemporary Patterns of Management of Tetralogy of Fallot:Data from a Single Center in China

Background:There is scarce research on large cohorts with tetralogy of Fallot(TOF)from China.The database in Fuwai Hospital was reviewed to ascertain current trends in the management of TOF and to determine the prevalence of various surgical techniques and the optimal early outcome.Methods:This cross-sectional study included 1861 patients who underwent surgery between 2012 and 2017 and were aged 0-18 years old with a primary diagnosis of TOF.A total of 1760 eligible patients were included in the analyses.Results:A total of 1683 patients underwent repair of TOF as a one-stage operation(primary repair).Sixty-one patients underwent repair of TOF after prior palliation.Of patients who underwent one-stage repair(n=1683):858 were 6 months to 1 year old,421 were 1 to 2 years old,251 were 2-18 years old,and 145 were 3 to 6 months old.Of patients who underwent repair following prior palliation(n=61),58(95.1%)were older than 1 year of age.Of 1744 complete repairs,986(56.0%)had annulus-sparing(AS)repair.Total in-hospital mortality was 15 of 1744(0.9%)for complete repair(including one-stage and staged repairs).The total incidence of the optimal early outcome was 78.2%in terms of a composite of the absence of death in the first year,significant right ventricular outflow tract obstruction,significant pulmonary valve insufficiency,or catheter or surgical reintervention.Conclusions:Surgical correction in patients with TOF can achieve an acceptable outcome in terms of death and reintervention.Primary repair at 6 months to 1 year of age is the most prevalent strategy in our centre.However,the relatively high incidence of early undesirable surgical adequacy of the pulmonary valve(PV)represents a wake-up call.

The Clinical Application Value of Selective Unifocalization in the Treatment of Severe Pulmonary Artery Atresia with Ventricular Septal Defect

Background:This study aims to explore the efficacy of selective unifocalization(UF)for major aortopulmonary collateral arteries(MAPCAs)unifocalization in children with pulmonary atresia with ventricular septal defect(PA/VSD).Methods:A retrospective analysis of 13 patients with PA/VSD/MAPCAs who underwent surgery from June 2017 to December 2019.Sex,age,preoperative cardiovascular angiography test results and McGoon ratio were collected.The properties of the collateral arteries were evaluated by angiography,and selective UF for the“dendritic”MAPCAs and ligation of MAPCAs demonstrating distortion and resistance.Results:A total of 13 severe patients underwent one-stage repair,of which 1 case underwent ventricular septal fenestration and died after 2 weeks of ECMO support.The median age was 37 months,and a median weight was 14.0 kg.A right ventricular to aortic systolic pressure ratio(pRV/pAo)of no more than 0.5 was achieved in 12 living patients.Conclusion:Selective unifocalization based on MAPCAs morphology can achieved a good outcome at the early stage.This surgical concept might be provided a novel insight into treatment for some of the subgroups presenting with this complex form of PA/VSD/MAPCAs.

Geometric nonlinear formulation for curved beams with varying curvature

Based on exact Green strain of spatial curved beam, the relation for plane curved beam with varying curvature is derived nonlinear strain-displacement Instead of using the previous straight beam elements, curved beam elements are used to approximate the curved beam with varying curvature. Based on virtual work principle, rigid-flexible coupling dynamic equations are obtained. Physical experiments were carried out to capture the large overall motion and the strain of curved beam to verify the present rigid-flexible coupling formulation for curved beam based on curved beam element. Numerical results obtained from simulations were compared with those results from the physical experiments. In order to illustrate the effectiveness of the curved beam element methodology, the simulation results of present curved beam elements are compared with those obtained by previous straight beam elements. The dynamic behavior of a slider-crank mechanism with an initially curved elastic connecting rod is investigated. The advantage of employing generalized-or method is pointed out and the special nonlinear dynamic characteristics of the curved beam are concluded.

Editorial:Recent development of dynamic formulations and numerical methods on multibody system

The 6th Asian Conference on Multibody Dynamics （ACMD 2012） has been successfully held in Shang- hai China organized by Shanghai Jiao Tong University, hosted by the Chinese Society of Theoretical and Ap- plied Mechanics, division of dynamics and control, the Japan Society of Mechanical Engineers, the Korean Society of Mechanical Engineers, International Federation for the Promotion of Mechanism and Machine Science and International Steering Committee of Asian Conference on Multibody Dynamics.

WC Grain Growth Behavior During Selective Laser Melting of WC-Co Cemented Carbides

Scanning strategy is a critical parameter for selective laser melting(SLM)processing of metals,alloys as well as metalceramic composites,while related research has rarely been reported yet,especially for additive manufacturing of WC–Co cemented carbides.In this study,three scanning strategies,i.e.,stripe,checkerboard,and spiral scanning,were used for additive manufacturing of WC-32Co cemented carbides.Checkerboard scanning leads to the highest relative density of 96%.Stripe scanning results in the largest average WC grain size followed by checkerboard and spiral scanning.SLM-processed carbides demonstrate agglomeration of WC grains mixed with isolated Co pools and pores.The WC grain growth mechanisms of SLM-processed cemented carbides include mosaic agglomeration growth and incomplete and uneven step growth regardless of scanning strategies.

Tribological properties of oil-impregnated polyimide in double-contact friction under micro-oil lubrication conditions

Oil-impregnated porous polyimide(iPPI)materials are usually used as retainer for bearings.In these bearings,balls and rings,balls and retainers are two different kinds of contact.In this paper,the friction and wear properties of iPPI were investigated using steel(disc)–steel(ball)–iPPI(pin)double-contact friction test rig for simulating the actual contact in bearings.The results show that compared with that of iPPI–steel single contact,the friction coefficient of iPPI–steel in double contacts is lower and decreases with the amount of additional oil.The surface of iPPI in single contact suffers more wear compared with that in double contacts.Different from single contact,the worn surfaces of iPPI in double contacts are blackened.The Raman spectra of worn surfaces of balls and discs indicate thatα-Fe_(2)O_(3) and Fe_(3)O_(4) were formed during rubbing of the double contacts.Many nanoscale iron oxide particles are found on the worn surfaces of iPPI in double contacts;on the contrary,few particles could be found on the surface in single contact.In double-contact friction,the nanoscale wear debris penetrates inside the iPPI material through the process of extruding and recycling of oil,which is the mechanism of the blackening of the iPPI worn surfaces.The studies show that the double-contact friction method is a new and effective method to study the friction in bearings,especially for those with polymer retainer.

A long non-coding RNA LncSync regulates mouse cardiomyocyte homeostasis and cardiac hypertrophy through coordination of miRNA actions

Dear Editor,Maintenance of cardiomyocyte(CM)homeostasis is essential for normal heart function.Long-term imbalance in heart homeostasis could elicit irreversible adaptive change in cell structure and function and tissue architecture,exemplified as cardiac hyper-trophy and fibrosis,and eventually develop into heart failure(Shiojima et al.,2005).Therefore,identifying new genes and path-ways regulating CM homeostasis may help better understand the cause of cardiac hypertrophy.

A new 2D van der Waals material with air stability and in-plane anisotropy

1.Text 2D van der Waals materials possess intriguing features[1],especially optically,such as high nonlinear optical responses[2],broadband spectral response[3],and accessible exciton effects[4].Unlike conventional 2D materials with in-plane isotropy,such as graphene and M0S_(2),2D van der Waals materials with in-plane anisotropic possess in-plane low symmetry structure,inducing the in-plane anisotropic physical properties.Meanwhile,they can be easily moved to various substrates without lattice-matching problems.

Mandatory information disclosure and innovation:Evidence from the disclosure of operational information

We use a quasi-natural experiment wherein the Shanghai Stock Exchange requires listed companies in certain industries to disclose operational information and a staggered difference-in-differences model to examine the impact of mandatory information disclosure on corporate innovation.We find that companies subject to mandatory operational information disclosure show significantly increased innovation.This effect is pronounced for companies classified as non-state-owned enterprises,facing severe financing constraints and a high degree of shareholder tunneling behavior and in competitive and high-tech industries.Although mandatory operational information disclosure reduces their competitive advantage,companies appear to compensate by increasing innovation.Our study highlights the positive impact of mandatory operational information disclosure,indicating that it contributes to the highquality development of both capital markets and companies.

Role of Co Content on Densification and Microstructure of WC–Co Cemented Carbides Prepared by Selective Laser Melting

WC–Co cemented carbides, well-known as the conventional tooling materials, have not been successfully produced by one step additive manufacturing processes such as selective laser melting(SLM) yet. The microstructure evolution as well as WC grain growth behavior has rarely been investigated in detail during SLM process. In this study, the WC–Co cemented carbides with different Co contents(12–32 wt%) were prepared by optimized SLM processes for comparative investigation of densification behavior, microstructure characterization and mechanical property. The increase in Co content in feedstock carbide granules can improve the densification behavior during SLM process. The SLM processed WC-12 Co shows larger average WC grain size and higher percentage of coarser WC grains as compared with both WC-20 Co and WC-32 Co. The microstructure characterization, combined with finite element simulation, shows the WC grain growth mechanisms include agglomeration and dissolution-deposition of WC during SLM process and agglomeration of WC is an important mechanism especially for WC–Co cemented carbides with Co content as low as 12 wt%. The comparison between horizontal(perpendicular to the SLM laser beam) and vertical(parallel to the SLM laser beam) cross sections of carbides shows that SLM process introduces a certain degree of microstructure and mechanical behavior anisotropy for WC-12 Co, WC-20 Co, and WC-32 Co.

Effective enhanced model for a large deformable soft pneumatic actuator

Soft pneumatic actuators have been widely used for implementing sophisticated and dexterous movements,due to numerous fascinating features compared with their rigid counterparts.Relatively speaking,modeling and analysis of an entire soft pneumatic actuator considering contact interaction between two adjacent air chambers is extremely rare,which is exactly what we are particularly interested in.Therefore,in order to establish an accurate mechanical model and analyze the overall configuration and stress distribution for the soft pneumatic actuator with large deflection,we consider the contact interaction of soft materials rather than hard materials,to produce an effective enhanced model for soft contact of a large deformable pneumatic actuator.In this article,a multiple-point contact approach is developed to circumvent the mutual penetration problem between adjacent air chambers of the soft actuator that occurs with the single-point contact approach employed in linear elastic rigid materials.In contrast to the previous simplified rod-based model that did not focus on contact interaction which was adopted to clarify the entire deformation of the actuator,the present model not only elaborates nonlinear large deformation and overall configuration variations,but also accurately delineates stress distribution law inside the chamber structure and the stress concentration phenomenon.By means of a corresponding static experiment,a comparison of the simulation results with experimental data validates the effectiveness and accuracy of this model employing a multiple-point contact approach.Excellent simulation of the actual bending deformation of the soft actuator is obtained,while mutual penetration is successfully circumvented,whereas the model with single-point contact cannot achieve those goals.Finally,as compared with the rod-based model,the results obtained using the proposed model are more consistent with experimental data,and simulation precision is improved.

土壤与粗糙刚体相互作用的二维离散元多体耦合动力学建模

土壤与刚体系统相互作用的研究是世界各国探索月球和火星的一项重要工作.为了研究干沙土的力学性质,离散单元法(DEM)是一种比较精确的模拟方法.但它不适用于相互接触、因约束而连接或因几何结构而具有复杂惯性特性的物体.为解决这一问题,文章提出一种二维离散元多体动力学建模方法,该方法考虑了颗粒球与包括光滑刚体和粗糙刚体在内的多体系统之间的接触和摩擦.在这项工作中,土壤场采用二维DEM建模,约束刚体系统的动力学采用笛卡儿方法建模.针对球形离散单元和粗糙刚体之间的相互作用提出一种检测算法.此耦合方法的优点是能够同时捕获两个响应.最后通过三球碰撞和矩形杆与三球碰撞的仿真实验,验证了程序的正确性.在此基础上,对齿轮在颗粒物中的运动进行了分析,结果表明,六齿30°倾角的齿轮具有最快的前进速度.在地外物体中,车轮抓地力变差,但随着重力加速度和车轮载荷的减小,前进速度先增大后减小,这证明了耦合二维DEM和多体动力学程序在解决工程问题中的有效性.

Feasibility and Surgical Effect of Annulus Sparing in Consecutive Patients with Tetralogy of Fallot:A Retrospective Cohort Study

Objective:Annulus-sparing(AS)repair for tetralogy of Fallot(TOF)with a dysplastic pulmonary valve annulus(PVA)is a challenging procedure and is controversial.This study aimed to assess the feasibility and surgical effect of AS repair versus transannular patch enlargement(TAPE)repair,especially in individuals with dysplastic pulmonary valves.Methods:This retrospective cohort study included 375 pediatric patients with a primary diagnosis of TOF in the Center for Pediatric Cardiac Surgery of Fuwai hospital from January 2014 to June 2017.Among them,60 consecutive and nonselective patients underwent 1-stage repair of TOF with aggressive PVA-preserving strategies performed by a single surgeon were enrolled in AS cohort.In AS cohort,patients were divided into AS,PVA z-score≥−2 group(33 patients)and AS,PVA z-score<−2 group(27 patients).During the same period,315 patients underwent TAPE repair by other surgeons were enrolled as TAPE cohort,of these,87 patients with PVA z-score≥−2 were excluded.From the 228 patients in the TAPE group,27 cases were selected as TAPE,PVA z-score<−2 group according to the propensity score and 1:1 ratio with AS,PVA z-score<−2 group.The primary outcome was a composite of reintervention,significant pulmonary regurgitation,and significant annular peak gradient(APG).Kaplan-Meier curve was plotted to show the survival rate of severe pulmonary regurgitation.Results:One death occurred after the TAPE operation in TAPE group,and 1 patient in the AS z≥−2 group needed reintervention with a balloon.After a median follow-up of(30.3±11.6)months,compared with AS z≥−2 group,there was no difference in the technical performance score for severe pulmonary stenosis(APGs>20 mmHg)in the AS z<−2 group.Compared with TAPE,AS repair was often accompanied by a postoperative APGs over 20 mmHg(P=0.001).More patients underwent TAPE suffered from moderate or severe pulmonary regurgitation than those who received AS repair(20(74.1%)vs.7(26.0%),P<0.001).AS repair was associated with a shorter duration of mechanical ventilation(20 vs.29 hours,P=0.039),faster discharge from the intensive care unit(2.0 vs.4.0 days,P=0.022)and shorter postoperative hospitalization(8.0 vs.11.0 days,P=0.008)compared with TAPE.Conclusions:APG demonstrated an upward trend in the TAPE group and a downtrend in the AS group after discharge from hospital.AS repair had an acceptable surgical effect in TOF patients,even in those with a dysplastic PVA.A higher APG remained upon hospital discharge in dysplastic patients with AS,but a downward trend was observed over time.