Comparison and analysis of two Coulomb friction models on the dynamic behavior of slider-crank mechanism with a revolute clearance joint

The objective of this study is to investigate the effects of the Coulomb dry friction model versus the modified Coulomb friction model on the dynamic behavior of the slider-crank mechanism with a revolute clearance joint. The normal and tangential forces acting on the contact points between the journal and the bearing are described by using a Hertzian-based contact force model and the Coulomb friction models, respectively.The dynamic equations of the mechanism are derived based on the Lagrange equations of the first kind and the Baumgarte stabilization method. The frictional force is solved via the linear complementarity problem(LCP) algorithm and the trial-and-error algorithm.Finally, three numerical examples are given to show the influence of the two Coulomb friction models on the dynamic behavior of the mechanism. Numerical results show that due to the stick friction, the slider-crank mechanism may exhibit stick-slip motion and can balance at some special positions, while the mechanism with ideal joints cannot.

Dynamics of luffing motion of a hydraulically driven shell manipulator with revolute clearance joints

In this study,a modeling method for investigating the dynamic characteristics of a hydraulically driven shell manipulator with revolute clearance joints is presented.This model accounts for the effect of the clearance,the flexibility of the rotating beam,and the coupled dynamic characteristics of the hydraulic cylinder.A modified contact force model was developed to simulate the physical properties of realistic revolute joints with small clearances,heavy loads,and variable contact stiffnesses and damping coefficients with variations of the indentations.Considering the strong coupling relationship between the hydraulic cylinder and the flexible beam,a system equation of motion combining the state variables of the hydraulic cylinder and mechanical system was established.The complex nonlinear friction force of the hydraulic cylinder motion was constructed using a modified Lu Gre model,and the parameters of the friction model were identified using intelligent identification algorithms.Moreover,a test system for the shell manipulator was established to achieve experimental validation.Finally,the effects of the clearance size and the stiffness of the cylinder support on the dynamic response were investigated.

Dynamic Investigations on the Wear Behavior of a 3D Revolute Joint Considering Time-Varying Contact Stiffness: Simulation and Experiment

The existence of the relative radial and axial movements of a revolute joint’s journal and bearing is widely known.The three-dimensional(3D)revolute joint model considers relative radial and axial clearances;therefore,the freedoms of motion and contact scenarios are more realistic than those of the two-dimensional model.This paper proposes a wear model that integrates the modeling of a 3D revolute clearance joint and the contact force and wear depth calculations.Time-varying contact stiffness is first considered in the contact force model.Also,a cycle-update wear depth calculation strategy is presented.A digital image correlation(DIC)non-contact measurement and a cylindricity test are conducted.The measurement results are compared with the numerical simulation,and the proposed model’s correctness and the wear depth calculation strategy are verified.The results show that the wear amount distribution on the bearing’s inner surface is uneven in the axial and radial directions due to the journal’s stochastic oscillations.The maximum wear depth locates where at the bearing’s edges the motion direction of the follower shifts.These find-ings help to seek the revolute joints’wear-prone parts and enhance their durability and reliability through improved design.

Dynamics Response and Non⁃linear Characteristics Analysis of Complex Planar 2⁃DOF Mechanism with Revolute Clearances

There are clearances in mechanism because of manufacture and assembly error,which reduces operation life and working accuracy of mechanism and has a great impact on dynamical responses.At the moment,research in this area mainly focuses on single degree⁃of⁃freedom mechanism considering one clearance,while research of multi⁃DOF mechanism considering multi⁃clearance is less.With the purpose of studying the dynamical characteristics of complex multi⁃DOF mechanism with multi⁃clearances,a dynamic model was developed.The dynamic responses of 2⁃DOF mechanism with two clearances under different positions,values,and numbers of clearance were analyzed.The displacement,velocity,acceleration,collision force,and the axis trajectory at clearance were then given.In addition,there is a limited amount of literature on chaotic phenomena,which mainly focuses on the chaotic phenomena of end⁃effector of mechanism.But in this paper,the non⁃linear characteristics were analyzed by chaotic phenomenon of clearance joint,then chaotic phenomenon was identified by Poincarémappings and phase diagrams.Bifurcation diagrams were given.The results will offer a reliable technical support for the study of dynamical responses of planar mechanisms and the analysis of chaotic phenomena.

Experimental Study of the Motion Modes of a Planar Mechanical System with Multi-Clearance Revolute Joints

Clearances in joints of a mechanical multibody system can induce impulsive forces, leading to vibrations that compromise the system’s reliability, stability, and lifespan. Through dynamic analysis, designers can investigate the effects of the clearances on the dynamics of the multibody system. A revolute joint with clearance exhibits three motions which are;free-flight, impact and continuous contact motion modes. Therefore, a multibody system with n-number of revolute clearance joints will exhibit 3n motion modes which are a combination of the three motions in each joint. This study investigates experimentally the nine motion modes in a mechanical system with two revolute clearance joints. A slider crank mechanism has been used as the demonstrative example. We observed that the experimental curve exhibits a greater impact compared to the simulation curve. In conclusion, this experimental investigation offers valuable insights into the dynamics of planar mechanical systems with multiple clearance revolute joints. Utilizing a slider-crank mechanism for data acquisition, the study successfully confirmed seven out of nine motion modes previously identified in numerical research. The missing modes are attributed to inherent complexities in real-world systems, such as journal-bearing misalignment.

An improved practical model for wear prediction of revolute clearance joints in crank slider mechanisms

A stationary clearance link algorithm(SCLA)for calculating the reaction-force of revolute clearance joints in crank slider mechanisms is proposed in this paper.The SCLA is more efficient than other algorithms of the same accuracy.Furthermore,based on the Winkler foundation model,an unsymmetrical Winkler foundation model and a double elastic layer Winkler model are proposed.By integrating a dynamic model and the unsymmetrical Winkler foundation model with Archard wear model,an improved integrated wear prediction model is also generated.A series of experiments have been performed to compare with the predicted analysis data,and the results showed a good agreement.As a real industry application,with the double elastic layer Winkler model,the integrated wear prediction model was successfully used to predict the wear depth of the joint bearing(bimetallic bearing)for the cantilever crane of a concrete pump truck of Sany Heavy Industry.

Dynamics modeling and error analysis for antenna pointing mechanisms with frictional spatial revolute joints on SE(3)

This paper presents a non-smooth multibody dynamic formulation and error analysis of an antenna pointing mechanism including frictional spatial revolute joints(FSRJs)with small clearance in the framework of the special Euclidian group SE(3).The formulation leads to an inertial frame-invariant,a compact and unified description for rigid bodies and spatial revolute joints(SRJs).The geometric constraint of the bearing is covered by four open semi-cylinders,which can be treated as bilateral constraints assuming that the impact effects are negligible.The frictional contact problem is formulated as a horizontal linear complementary problem(HLCP),which is embedded in the Lie-group integration scheme.Error of the antenna pointing mechanism is modeled by means of the adjoint transformation and POE-based formula.The evolution of errors is obtained through the solution of non-smooth dynamics.The obtained numerical results illustrate the influences of FSRJs in dynamics modeling and error analysis of the antenna pointing mechanism.

颅脑CT灌注成像及磁共振成像在脑梗死患者中的应用

目的分析颅脑CT灌注成像及磁共振成像对脑梗死患者的诊断价值。方法选取2022-03—2023-05在江苏省中西医结合医院就诊的80例疑似脑梗死患者为研究对象,对比分析GE Revolution CT颅脑灌注成像、磁共振成像及联合检查的敏感性、特异性、准确性,制作3种影像学检查的受试者工作特征(ROC)曲线。结果根据患者病情和临床综合诊断确诊,80例疑似脑梗死患者中脑梗死阳性69例(86.25%),脑梗死阴性11例(13.75%)。3种影像学检查方法的灵敏度、准确率比较,从高到低依次为联合检查、GE Revolution CT颅脑灌注成像检查、磁共振成像检查,差异有统计学意义(P<0.05)。GE Revolution CT颅脑灌注成像检查、磁共振成像检查、联合检查诊断脑梗死的ROC曲线下面积(AUC)分别为0.8109、0.7688、0.8682。结论GE Revolution CT颅脑灌注成像与磁共振成像检查的联合应用,有利于提高脑梗死患者诊断的灵敏度、准确率及AUC水平。

Revolution CT联合不同权重ASIR-V在胸痛三联征成像中的应用价值比较

目的探讨Revolution CT联合不同权重多模型迭代重建技术(ASIR-V)在胸痛三联征(TRO)成像中的应用价值。方法选取我院2022年8月~2023年3月收治的90例胸痛患者进行研究,入院后接受TRORevolution CT平扫。按随机数字表法分成滤波反投影(FBP)组与ASIR-V组各45例。FBP组采用FBP技术进行图像重组,ASIR-V组采用不同权重(10%、30%、50%、70%、90%)前置ASIR-V技术重组。记录两组辐射剂量长度乘积(DLP)、有效剂量(ED),比较不同重组方式及不同权重下冠状动脉、升主动脉、降主动脉、肺动脉干的平均CT值、噪声值、信噪比(SNR)、对比信噪比(CNR),由2名经验丰富的影像科医生进行主观图像质量评分。结果ASIR-V组DLP、ED低于FBP组(P<0.05)。ASIR-V不同权重的血管腔噪声值低于FBP,血管腔SNR、CNR与主观图像质量评分高于FBP(P<0.05)。ASIR-V权重50%、70%、90%的噪声值低于ASIR-V权重10%、30%的噪声值(P<0.05)。ASIR-V权重50%、70%、90%的SNR、CNR高于ASIR-V权重10%、30%的SNR、CNR(P<0.05)。ASIR-V权重50%、70%的主观评分高于ASIR-V权重10%、30%、90%的主观评分(P<0.05)。结论Revolution CT联合ASIR-V技术能减少辐射剂量,ASIR-V权重50%、70%时对血管腔与解剖结构的显示良好,血管腔噪声值较低,SNR、CNR较高,能满足诊断需求。

Artificial selection of the Green Revolution gene Semidwarf 1 is implicated in upland rice breeding

Semidwarf breeding has boosted crop production and is a well-known outcome from the first Green Revolution. The Green Revolution gene Semidwarf 1(SD1), which modulates gibberellic acid(GA) biosynthesis, plays a principal role in determining rice plant height. Mutations in SD1 reduce rice plant height and promote lodging resistance and fertilizer tolerance to increase grain production. The plant height mediated by SD1 also favors grain yield under certain conditions. However, it is not yet known whether the function of SD1 in upland rice promotes adaptation and grain production. In this study, the plant height and grain yield of irrigated and upland rice were comparatively analyzed under paddy and dryland conditions. In response to dryland environments, rice requires a reduction in plant height to cope with water deficits. Upland rice accessions had greater plant heights than their irrigated counterparts under both paddy and dryland conditions, and appropriately reducing plant height could improve adaptability to dryland environments and maintain high grain yield formation. Moreover, upland rice cultivars with thicker stem diameters had stronger lodging resistance, which addresses the lodging problem. Knockout of SD1 in the upland rice cultivar IRAT104 reduced the plant height and grain yield, demonstrating that the adjustment of plant height mediated by SD1 could increase grain production in dryland fields. In addition, an SD1 genetic diversity analysis verified that haplotype variation causes phenotypic variation in plant height. During the breeding history of rice, SD1 allelic mutations were selected from landraces to improve the grain yield of irrigated rice cultivars, and this selection was accompanied by a reduction in plant height. Thus, five known mutant alleles were analyzed to verify that functional SD1 is required for upland rice production. All these results suggest that SD1 might have undergone artificial positive selection in upland rice, which provides further insights concerning greater plant height in upland rice breeding.

Callfor Papersfor Special Issue Innovative Pharmaceutical Research Facilitated by Ai

Al is revolutionizing the current paradigm of pharmaceutical research,addressing the challenges encountered at all stages of the process.Al driven drug discovery is based on biomedical big data and new algorithms to identify drug targets,screen and optimize active compounds,analyze drug properties,and facilitate drug production and quality control.On this basis,we are organize this special issue entitled“Innovative Pharmaceutical Research Driven by Al”,to collect Research articles,Review papers,and Short communications,facilitating pharmaceutical research.

基于体表面积的碘对比剂个性化方案在冠状动脉CT血管造影增强效能中的应用

目的:探讨体表面积(BSA)的碘对比剂个性化方案在受检者自由呼吸状态下冠状动脉CT血管造影(CTA)效能增强的可行性。方法:将临床疑似冠状动脉疾病的30例患者纳入研究,按BSA分为两组:BSA≤1.6 m^(2)的患者为小BSA组,BSA>1.6 m^(2)的患者为大BSA组。然后基于BSA计算碘对比剂的用量[造影剂用量(mL)=(BSA×10/碘浓度)],造影剂注射时间为10 s。利用Revolution CT在患者自由呼吸状态下对冠状动脉进行造影成像。由具备5年以上胸部影像诊断经验的医师对数据进行主观和客观图像质量评分,采用5分法对A组和B组图像进行主观评分;同时测量两组患者降主动脉、升主动脉、左冠状动脉主干、左前降支、左回旋支、右冠状动脉主干6支血管的CT值及信噪比(SNR)值。结果:两组图像的主观评分数值均能达到3分以上,可满足诊断要求,且两位医师主观评分的一致性(ICC)较好(分别为0.81、0.71)。客观评分结果显示两组图像冠状动脉的显影效果较好,且冠状动脉CT值和SNR值差异无统计学意义(P>0.05)。结论:基于BSA的碘对比剂个性化方案具有临床可行性,冠状动脉血管的强化程度合适且均一,可满足临床诊断要求。

Integrating GPT into the Journalism and Communication Industries:The Technological Logic,Ecosystem Reconstruction,and Ethical Chal enges

Generative AI,represented by GPT(Generative Pre-trained Transformer),is now leading the technological revolution and is reconstructing the journalism and communication industries'ecosystems because of its powerful generative capacity and diverse range of outputs.While GPT is busy revolutionizing and innovating the production of news content,working patterns,and operation modes,it has also given rise to ethical concerns in regard to news authenticity,data security,humanistic values,and other related aspects.Therefore,it is imperative to initiate strategies and approaches,such as establishing a mechanism for verifying information authenticity,enhancing data security and privacy regulations,and instituting an ethical supervision and governance framework for AI,in order to facilitate the systematic advancement of AI-based news production while reinstating public trust.

2024全球十大趋势

In 2023, momentous changes of a like not seen in a century accelerated across the globe. The world as a whole was in a period of turbulence and change: regional conflicts cropped up, major-country competition became more complex, climate change deteriorated, and the scientific and technological revolution accelerated. The international security situation was worrisome, against which China demonstrated its sense of duty as a responsible country. Looking forward to 2024, in the face of an unstable, uncertain, and insecure external environment, China will advance its four global initiatives in a coordinated manner, contributing positive energy to the world.

World Industrial Revolutions and the Development of Artificial Intelligence System

The objective-scientific conclusions obtained from the researches conducted in various fields of science prove that era and worldview are in unity and are phenomena that determine one another,and era and worldview are the most important phenomena in the understanding of geniuses,historical events,including personalities who have left a mark on the history of politics,and every individual as a whole.And it is appropriate to briefly consider the problem in the context of human and personality factors.It is known that man has tried to understand natural phenomena since the beginning of time.Contact with the material world naturally affects his consciousness and even his subconscious as he solves problems that are important or useful for human life.During this understanding,the worldview changes and is formed.Thus,depending on the material and moral development of all spheres of life,the content and essence of the progress events,as the civilizations replaced each other in different periods,the event of periodization took place and became a system.If we take Europe,the people of the Ice Age of 300,000 years ago,who engaged in hunting to solve their hunger needs,in other words,the age of dinosaurs,have spread to many parts of the world from Africa,where they lived in order to survive and meet more of their daily needs.The extensive integration of agricultural Ice Age People into the Earth included farming,fishing,animal husbandry,hunting,as well as handicrafts,etc.,and has led to the revolutionary development of the fields.As economic activities led these first inhabitants of the planet from caves to less comfortable shelters,then to good houses,then to palaces,labor activities in various occupations,including crafts,developed rapidly.Thus,the fads of the era who differed from the crowd(later this class will be called personalities,geniuses...-Kh.G.)began to appear.If we approach the issue from the point of view of history,we witness that the world view determines the development in different periods.This idea can be expressed in such a way that each period can be considered to have developed or experienced a crisis according to the level of worldview.In this direction of our thoughts,the question arises:So,what is the phenomenon of worldview of this era-XXI century?Based on the general content of the current events,characterized as the globalization stage of the modern world,we can say that the outlook of the historical stage we live in is based on the achievements of the last stage of the industrial revolution.In this article,by analyzing the history of the artificial intelligence system during the world industrial revolutions,we will study both the concept of progress of the industrial revolutions and the progressive and at the same time regressive development of the artificial intelligence system.

The Revolution that Reshapes Lifestyles

While navigating the brave new world of online shopping,China should strike a balance between embracing the future and preserving the traditions that enrich its cultural fabric.IN the bustling streets of China,a quiet revolution has taken place,reshaping the way people shop and interact with the market.E-commerce has emerged as a dominant force,offering a plethora of products and services at the fingertips of tens of millions.From the tiny needle to the grandest household appliances,from branded shoes to fresh fruits and vegetables,everything is just a click away.

World’s Energy Transition and Chinese-style Modern Energy Revolution under Carbon Neutrality (Ⅱ)

Chinese-style modernization emphasizes the harmonious coexistence of man and nature and actively yet prudently promotes carbon peak and carbon neutrality.It delves deeply into the energy revolution,upholding the following principles:the“independence”of energy production,the“green”energy supply,the“security”of energy reserves,the“efficiency”of energy consumption,the“intelligence”of energy management,and the“economy”of energy costs.Efforts are being made to accelerate the planning and construction of a new type of energy system that is green and smart,with new energy,new electricity,new stored energy,and new smart energy as the mainstays,to ensure energy security.Currently,China is an energy power but not an energy superpower,and its energy consumption structure still needs further optimization.China’s new energy security strategy is composed of energy consumption revolution,energy supply revolution,energy technology revolution,and energy system revolution,complemented by comprehensive strengthening of international cooperation.This approach is aimed at advancing China’s energy revolution and transforming the nation’s energy supply pattern and shifting from a consumption mix in 2022.

Revolution 256 CT轴扫模式下不同心率患者冠状动脉CT血管成像的图像质量及辐射剂量分析

目的:本研究旨在评估采用Revolution 256 CT扫描仪进行冠状动脉CT血管成像(CCTA)时不同心率(HR)患者的图像质量和辐射剂量。方法:收集2022年3月—2023年3月期间90例不同心率患者的数据,根据入组时的心率将其分为三组:低心率组(HR<60bpm)、正常心率组(60bpm≤HR≤80bpm)和高心率组(HR>80bpm),各组人数均为30例,每组患者均采用Revolution 256 CT扫描仪进行CCTA检查,比较不同心率患者的图像质量和辐射剂量。结果:低心率组的图像质量最高,高心率组的图像质量最差,数据差异明显(P<0.05);统计分析表明,高心率组和低心率组在辐射剂量方面存在显著差异(P<0.05)。结论:使用Revolution 256 CT扫描仪进行CCTA检查时,低心率组和高心率组患者的图像质量均能够达到诊断标准,而且辐射剂量相对较低,因此,在使用Revolution256 CT扫描进行CCTA检查时,不同心率的患者均可采用该检查方式,无需特殊处理。

Video Games and School Performances of Dakar High School Students

The triptych (Smartphones, Video games, adolescents) has imposed itself on the collective consciousness in the form of questioning to the point of becoming a social phenomenon. It thus raises concerns about the uses that adolescents make of it and the effects on their academic performance, which we proposed to study among middle school students from the Dakar academy inspection. Where appropriate, we used mixed methods with the collection techniques of questionnaire survey, semi-structured interviews respectively with middle school students, adults (parents, supervisors, teachers, etc.), participant observation and literature review. Concretely, before accessibility to video games, the middle school students were more idle and well-behaved, watched a lot of TV, played with their brothers and sisters or did household chores. The majority of young people had good, very good or excellent conduct and their averages were fair, fairly good or good. With access to a diverse digital environment, middle school students have passionately turned to video games. As a result, their learning time, concentration and submission to parental injunctions have declined significantly. This situation negatively affected their academic performance and encouraged bad behavior.

Introducing a 2nd Universal Space-Time Constant Can Explain the Observed Age of the Universe and Dark Energy

The purpose of this paper is to introduce new theoretical concepts as opposed to accepting the existence of dark entities, such as dark energy. This research sought to introduce a 2nd universal space-time constant, besides having a finite speed constant (speed of light in vacuum c). A finite universal age constant b is introduced. Namely, this paper shows that the changes in the Earth’s anomalistic year duration over time support the hypothesis of the age of the universe correlating with a maximum number of orbital revolutions constant. Neglecting the gravitational influence of other cosmological entities in the proximity of the Earth, the constant maximum number of revolutions is herewith determined solely by the Earth’s orbital revolutions around the Sun. The value of the universal age constant b is calculated to be around 13.8 billion orbital revolutions, derived out of an equation related to the changes in the Earth’s anomalistic year duration over time and the so-called Hubble tension. The above-mentioned calculated value b correlates well with the best fit to measured data of the cosmic microwave background radiation (CMBR) by the Planck spacecraft, the age of the observed universe is measured to be approximately 13.787 ± 0.020 billion years (2018 final data release). Developing a theory with this 2nd universal space-time constant b, being covariant with respect to the Lorentz transformations when time spans are large, gives results such as: A confirmation of the measured CMBR value of 13.787 ± 0.020 billion years. Correlating well with the observed expansion rate of the universe (dark energy). The universe’s expansion accelerating over the last four to five billion years.