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A Procedure for Trisecting an Acute Angle (Method 2)
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作者 Lyndon O. Barton 《Advances in Pure Mathematics》 2024年第4期204-213,共10页
This paper presents an alternate graphical procedure (Method 2), to that presented in earlier publications entitled, “A Procedure for Trisecting an Acute Angle” and “A Key to Solving the Angle Trisection Problem”.... This paper presents an alternate graphical procedure (Method 2), to that presented in earlier publications entitled, “A Procedure for Trisecting an Acute Angle” and “A Key to Solving the Angle Trisection Problem”. The procedure, when applied to the 30˚ and 60˚ angles that have been “proven” to be nottrisectable and the 45˚ benchmark angle that is known to be trisectable, in each case produced a construction having an identical angular relationship with Archimedes’ Construction, as in Section 2 on THEORY of this paper, where the required trisection angle was found to be one-third of its respective angle (i.e. DE’MA = 1/3 DE’CG). For example, the trisection angle for the 30˚, 45˚ and 60˚ angles were 10.00000˚, 15.00000˚, and 20.00000˚, respectively, and Section 5 on PROOF in this paper. Therefore, based on this identical angular relationship and the numerical results (i.e. to five decimal places), which represent the highest degree of accuracy and precision attainable by The Geometer’s Sketch Pad software, one can only conclude that not only the geometric requirements for arriving at an exact trisection of the 30˚ and 60˚ angle (which have been “proven” to be not-trisectable) have been met, but also, the construction is valid for any arbitrary acute angle, despite theoretical proofs to the contrary by Wantzel, Dudley, and others. 展开更多
关键词 Archimedes’ Construction College Geometry College Mathematics angle Trisection Famous Problems in Mathematics mechanism Analysis Geometer’s Sketch Pad
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Pressure Angle in Parallel Mechanisms: From Planar to Spatial 被引量:2
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作者 Zhao Qing Mei Jiangping +1 位作者 Song Tao Liu Songtao 《Transactions of Tianjin University》 EI CAS 2016年第5期411-418,共8页
This paper presents the evolution process of pressure angles from planar parallel mechanisms to spatial parallel mechanisms. Manipulability and condition number, which are frequently used in the optimum design of para... This paper presents the evolution process of pressure angles from planar parallel mechanisms to spatial parallel mechanisms. Manipulability and condition number, which are frequently used in the optimum design of parallel mechanisms, are introduced from serial robots at first. Then, both theoretical analysis and practical experiences demonstrate that these concepts seem imperfect when they are used in parallel mechanisms. For this reason, this paper introduces the pressure angles in planar 4-bar mechanisms to spatial parallel mechanisms, which include redundant parallel mechanisms. Two kinds of pressure angles extracted from the determinant of direct and indirect Jacobian matrices are investigated. Moreover, two comprehensive and visible global performance indices are defined, showing the advantages in evaluating the workspace, singularity and motion/force transmission capabilities. With a 2-DOF planar and a 3-DOF spatial parallel mechanism as examples, the application of the performance indices is investigated and compared with the condition number at last. The proposed concept can be extended to other spatial parallel mechanisms. 展开更多
关键词 pressure angle PERFORMANCE evaluation global PERFORMANCE INDEX parallel mechanism
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Effect of contact angle and helix angle on slide-roll ratio under the accelerated motion state of ball screw mechanism 被引量:3
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作者 Kong Deshun Wang Min Gao Xiangsheng 《Journal of Southeast University(English Edition)》 EI CAS 2017年第4期398-408,共11页
To study the effect of the contact angle and helix angle on slide-roll ratio at the ball contact points under the accelerated motion state of ball screw mechanisrm(B S M),the curve theory in differential geometry a d ... To study the effect of the contact angle and helix angle on slide-roll ratio at the ball contact points under the accelerated motion state of ball screw mechanisrm(B S M),the curve theory in differential geometry a d the homogeneous transformation matrix ae used to establish the acceleration kinematics model of BSM.The model can be used to describe the accelerated motion relationships among the screw,balls and nut,calculate the acceleration of relative motion at the contact points between the balls and raceways,and analyze five accelerated motion rules between the balls and raceways.It also conducts a simulation analysis of the slide-roll ratio relationship between the accelerations at the ball center and the contact point of ball under different contact angles and helix angles.As shownby the analysis,with the increase in the BSM’s contact angle,the slide-roll ratio at the contact points decreases,and the contact angle has a relatively significant effect on the slide-roll ratio.However,with the decrease in the BSM’helix angle,the slide-roll ratio at the contact points decreases,and the helix angle has a relatively insignificant effect on the slide-roll ratio.By measuring the accelerations of both the screw and nut under the accelerated motion state,it also verifies the existence of the slide-roll mixed motion at the ball contact point A between the ball and the screw racewayand pure rolling at the ball contact point B between the ball and the nut raceway during the accelerated motion. 展开更多
关键词 ball screw mechanism contact angle helix angle slide-roll ratio
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Improved contact angle measurement in multiphase lattice Boltzmann
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作者 钟兴国 刘阳莎 +2 位作者 姚怡辰 何冰 闻炳海 《Chinese Physics B》 SCIE EI CAS CSCD 2023年第5期537-543,共7页
Contact angle is an essential parameter to characterize substrate wettability.The measurement of contact angle in experiment and simulation is a complex and time-consuming task.In this paper,an improved method of meas... Contact angle is an essential parameter to characterize substrate wettability.The measurement of contact angle in experiment and simulation is a complex and time-consuming task.In this paper,an improved method of measuring contact angle in multiphase lattice Boltzmann simulations is proposed,which can accurately obtain the real-time contact angle at a low temperature and larger density ratio.The three-phase contact point is determined by an extrapolation,and its position is not affected by the local deformation of flow field in the three-phase contact region.A series of simulations confirms that the present method has high accuracy and gird-independence.The contact angle keeps an excellent linear relationship with the chemical potential of the surface,so that it is very convenient to specify the wettability of a surface.The real-time contact angle measurement enables us to obtain the dynamic contact angle hysteresis on chemically heterogeneous surface,while the mechanical analyses can be effectively implemented at the moving contact line. 展开更多
关键词 contact angle measurement contact angle hysteresis mechanical analysis lattice Boltzmann method
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A Simplified Graphical Procedure for Constructing a 10˚or 20˚Angle
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作者 Lyndon O. Barton 《Advances in Pure Mathematics》 2023年第7期442-448,共7页
This paper presents a simplified graphical procedure for constructing, using an unmarked straightedge and a compass only, a 10˚ to 20˚ angle, which is in other words, trisecting a 30˚ or 60˚ angle. The procedure, when... This paper presents a simplified graphical procedure for constructing, using an unmarked straightedge and a compass only, a 10˚ to 20˚ angle, which is in other words, trisecting a 30˚ or 60˚ angle. The procedure, when applied to the 30˚ and 60˚ angles that have been “proven” to be not trisectable, produced a construction having the identical angular relationship with Archimedes’ Construction, in which the required trisection angles were found to be 10.00000˚ and 20.00000˚ respectively (i.e. exactly one-third of the given angle or ∠E’MA = 1/3∠E’CG). Based on this identical angular relationship as well as the numerical results obtained, one can only conclude that the geometric requirements for arriving at an exact trisection of the 30˚ or 60˚ angle, and therefore the construction of a 10˚ or 20˚ angle, have been met, notwithstanding the theoretical proofs of Wantzel, Dudley, and others. Thus, the solution to the age-old trisection problem, with respect to these two angles, has been accomplished. 展开更多
关键词 Archimedes’ Construction College Geometry angle Trisection Trisection of an angle Famous Problems in Mathematics. Geometer’s Sketch Pad mechanisms mechanism Analysis Kinematics Trisector
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Hydraulic support stability control of fully mechanized top coal caving face with steep coal seams based on instable critical angle 被引量:2
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作者 屠世浩 袁永 +2 位作者 李乃梁 窦凤金 王方田 《Journal of Coal Science & Engineering(China)》 2008年第3期382-385,共4页
Analyzed the support instable mode of sliding,tripping,and so on,and believed the key point of the support stability control of fully mechanized coal caving face with steep coal seams was to maintain that the seam tru... Analyzed the support instable mode of sliding,tripping,and so on,and believed the key point of the support stability control of fully mechanized coal caving face with steep coal seams was to maintain that the seam true angle was less than the hydraulic support instability critical angle.Through the layout of oblique face,the improvement of support setting load,the control of mining height and nonskid platform,the group support system of end face,the advance optimization of conveyor and support,and the other control tech- nical measures,the true angle of the seam is reduced and the instable critical angle of the support is increased,the hydraulic support stability of fully mechanized coal caving face with steep coal seams is effectively controlled. 展开更多
关键词 steep coal seams instable critical angle support stability fully mechanized top coal caving control technology
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A Key to Solving the Angle Trisection Problem
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作者 Lyndon O. Barton 《Advances in Pure Mathematics》 2023年第9期625-634,共10页
This paper describes the methodology (or approach) that was key to the solution of the angle trisection problem published earlier in article entitled, “A Procedure For Trisecting An Acute Angle.” It was an approach ... This paper describes the methodology (or approach) that was key to the solution of the angle trisection problem published earlier in article entitled, “A Procedure For Trisecting An Acute Angle.” It was an approach that required first, designing a working model of a trisector mechanism, second, studying the motion of key elements of the mechanism and third, applying the fundamental principles of kinematics to arrive at the desired results. In presenting these results, since there was no requirement to provide a detailed analysis of the final construction, this information was not included. However, now that the publication is out, it is considered appropriate as well as instructive to explain more fully the mechanism analysis of the trisector in graphical detail, as covered in Section 3 of this paper, that formed the basis of the long sought solution to the age-old Angle Trisection Problem. 展开更多
关键词 Archimedes’ Construction College Geometry College Mathematics angle Trisection Trisector Famous Problems in Mathematics History of Mathematics mechanism Analysis Kinematics Geometer’s Sketch Pad
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Shear mechanical properties and fracturing responses of layered rough jointed rock-like materials
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作者 Xinxin Nie Qian Yin +7 位作者 Manchao He Qi Wang Hongwen Jing Bowen Zheng Bo Meng Tianci Deng Zheng Jiang Jiangyu Wu 《International Journal of Minerals,Metallurgy and Materials》 SCIE EI CAS CSCD 2024年第11期2417-2434,共18页
This study aims to investigate mechanical properties and failure mechanisms of layered rock with rough joint surfaces under direct shear loading.Cubic layered samples with dimensions of 100 mm×100 mm×100 mm ... This study aims to investigate mechanical properties and failure mechanisms of layered rock with rough joint surfaces under direct shear loading.Cubic layered samples with dimensions of 100 mm×100 mm×100 mm were casted using rock-like materials,with anisotropic angle(α)and joint roughness coefficient(JRC)ranging from 15°to 75°and 2-20,respectively.The direct shear tests were conducted under the application of initial normal stress(σ_(n))ranging from 1-4 MPa.The test results indicate significant differences in mechanical properties,acoustic emission(AE)responses,maximum principal strain fields,and ultimate failure modes of layered samples under different test conditions.The peak stress increases with the increasingαand achieves a maximum value atα=60°or 75°.Asσ_(n)increases,the peak stress shows an increasing trend,with correlation coefficients R²ranging from 0.918 to 0.995 for the linear least squares fitting.As JRC increases from 2-4 to 18-20,the cohesion increases by 86.32%whenα=15°,while the cohesion decreases by 27.93%whenα=75°.The differences in roughness characteristics of shear failure surface induced byαresult in anisotropic post-peak AE responses,which is characterized by active AE signals whenαis small and quiet AE signals for a largeα.For a given JRC=6-8 andσ_(n)=1 MPa,asαincreases,the accumulative AE counts increase by 224.31%(αincreased from 15°to 60°),and then decrease by 14.68%(αincreased from 60°to 75°).The shear failure surface is formed along the weak interlayer whenα=15°and penetrates the layered matrix whenα=60°.Whenα=15°,asσ_(n)increases,the adjacent weak interlayer induces a change in the direction of tensile cracks propagation,resulting in a stepped pattern of cracks distribution.The increase in JRC intensifies roughness characteristics of shear failure surface for a smallα,however,it is not pronounced for a largeα.The findings will contribute to a better understanding of the mechanical responses and failure mechanisms of the layered rocks subjected to shear loads. 展开更多
关键词 layered samples anisotropic angle joint roughness coefficient mechanical properties acoustic emission response fracturing evolution failure modes
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Stabilizing Mechanism and Running Behavior of Couplers on Heavy Haul Trains 被引量:2
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作者 XU Ziqiang WU Qing +2 位作者 LUO Shihui MA Weihua DONG Xiaoqing 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2014年第6期1211-1218,共8页
Published studies in regard to coupler systems have been mainly focused on the manufacturing process or coupler strength issues. With the ever increasing of tonnage and length of heavy haul trains, lateral in-train fo... Published studies in regard to coupler systems have been mainly focused on the manufacturing process or coupler strength issues. With the ever increasing of tonnage and length of heavy haul trains, lateral in-train forces generated by longitudinal in-train forces and coupler rotations have become a more and more significant safety issue for heavy haul train operations. Derailments caused by excessive lateral in-train forces are frequently reported. This article studies two typical coupler systems used on heavy haul locomotives. Their structures and stabilizing mechanism are analyzed before the corresponding models are developed. Coupler systems models are featured by two distinct stabilizing mechanism models and draft gear models with hysteresis considered. A model set which consists of four locomotives and three coupler systems is developed to study the rotational behavior of different coupler systems and their implications for locomotive dynamics. Simulated results indicate that when the locomotives are equipped with the type B coupler system, locomotives can meet the dynamics standard on tangent tracks; while the dynamics performance on curved tracks is very poor. The maximum longitudinal in-train force for locomotives equipped with the type B coupler system is 2000 kN. Simulations revealed a distinct trend for the type A coupler system. Locomotive dynamics are poorer for the type A case when locomotives are running on tangent tracks, while the dynamics are better for the type A case when locomotives are running on curved tracks. Theoretical studies and simulations carried out in this article suggest that a combination of the two types of stabilizing mechanism can result in a good design which can significantly decrease the relevant derailments. 展开更多
关键词 dynamic heavy haul train coupler systems stable mechanism coupler angle safety
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Analysis and Design of the Globoidal Indexing Cam Mechanism 被引量:3
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作者 FU Yan ming School of Mechanical and Electronic Engineering and Automation, Shanghai University, Shanghai 200072, China 《Advances in Manufacturing》 2000年第1期54-59,共6页
We first design and analyze the contour surface of the globoidal indexing cam with the aid of computer, and then do optimum design according to the requirements of dynamics. Finally, we discuss the problem of the pres... We first design and analyze the contour surface of the globoidal indexing cam with the aid of computer, and then do optimum design according to the requirements of dynamics. Finally, we discuss the problem of the pressure angle of the globoidal indexing cam mechanism in detail and put forward a new concept of equivalent pressure angle. 展开更多
关键词 globoidal indexing cam analysis of cam mechanism design of cam mechanism dynamics of mechanism pressure angle
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Mesoplasticity Approach to Studies of the Cutting Mechanism in Ultra-precision Machining 被引量:2
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作者 LEE WB Rongbin WANG Hao +2 位作者 TO Suet CHEUNG Chi Fai CHAN Chang Yuen 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2014年第2期219-228,共10页
There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plast... There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plasticity and continuum mechanics. Very few attempts, however, have been reported in ultra-precision machining studies. A mesoplasticity approach advocated by Lee and Yang is adopted by the authors and is successfully applied to studies of the micro-cutting mechanisms in ultra-precision machining. Traditionally, the shear angle in metal cutting, as well as the cutting force variation, can only be determined from cutting tests. In the pioneering work of the authors, the use of mesoplasticity theory enables prediction of the fluctuation of the shear angle and micro-cutting force, shear band formation, chip morphology in diamond turning and size effect in nano-indentation. These findings are verified by experiments. The mesoplasticity formulation opens up a new direction of studies to enable how the plastic behaviour of materials and their constitutive representations in deformation processing, such as machining can be predicted, assessed and deduced from the basic properties of the materials measurable at the microscale. 展开更多
关键词 ultra-precision machining cutting mechanism mesoplasticity shear angle prediction size effect micro-cutting force variation high frequency tool-tip vibration
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SMALL ANGLE NEUTRON SCATTERING INVESTIGATION OF Ni_(50)Mo(50)ALLOY AND ITS FRACTAL PROPERTIES
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作者 LI MeiyaShantou University,Shantou, Guangdong, ChinaCOWLAMNUniversity of Sheffield, Sheffield S3 7RH, UKCOCCOGUniversita di Sassari, via Vienna 2,07100 Sassari,Italy Manuscript received 10 May, 1994 《Acta Metallurgica Sinica(English Letters)》 SCIE EI CAS CSCD 1994年第2期139-144,共6页
Small angle neutron scattering(SANS) technique has been used to investigate the Ni_(50)Mo_(50) system prepared by mechanical alloying(MA). Significant changes of the scattering intensity have been observed among the s... Small angle neutron scattering(SANS) technique has been used to investigate the Ni_(50)Mo_(50) system prepared by mechanical alloying(MA). Significant changes of the scattering intensity have been observed among the samples with different milling time.Interesting fractal-like behavior of the sample system have been found and attempts have been made to determine the fractal dimensions. It is expected that the fractal dimension can be related to the different stages of MA to some extent. 展开更多
关键词 mechanical alloying small angle neutron scattering fractal dimension
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NOVEL METHOD OF REALIZING THE OPTIMAL TRANSMISSION OF THE CRANK-AND-ROCKERMECHANISM DESIGN
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作者 Fang Shijie Li LiDepartment of Mechanical Engineering,Yantai University,Yantai 264005, China 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2003年第1期31-33,共3页
A novel method of realizing the optimal transmission of the crank-and-rockermechanism is presented. The optimal combination design is made by finding the related optimaltransmission parameters. The diagram of the opti... A novel method of realizing the optimal transmission of the crank-and-rockermechanism is presented. The optimal combination design is made by finding the related optimaltransmission parameters. The diagram of the optimal transmission is drawn. In the diagram, therelation among mini-mum transmission angle, the coefficient of travel speed variation, theoscillating angle of the rocker and the length of the bars is shown, concisely, conveniently anddirectly. The method possesses the main characteristic. That it is to achieve the optimaltransmission parameters under the transmission angle by directly choosing in the diagram, accordingto the given requirements. The characteristics of the mechanical transmission can be improved togain the optimal transmission effect by the method. Especially, the method is simple and convenientin practical use. 展开更多
关键词 Crank-and-rocker mechanism Optimal transmission angle Coefficient oftravel speed variation
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Stiffness Analysis of Spherical Parallel Mechanism U_(P+R) with 2-DOF
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作者 Yu-Lin Zhou Long Yang +2 位作者 Bo Li Da-Xing Zeng Feng Gao 《Journal of Harbin Institute of Technology(New Series)》 EI CAS 2013年第4期41-47,共7页
As one of the typical less-mobility parallel mechanisms, the spherical parallel mechanism Up.s with two degrees of freedom (2-DOF) possess high order overconstraints, and the calculation of its stiffness is partly d... As one of the typical less-mobility parallel mechanisms, the spherical parallel mechanism Up.s with two degrees of freedom (2-DOF) possess high order overconstraints, and the calculation of its stiffness is partly different with general parallel mechanisms owing to the bars in each branch are assumed to be arc-shaped. By means of small deformation superposition principle, the relationship between the angle displacement and line displacement of moving platform and the forces acted on the branches were derived out. Based on the results of static analysis, the relationship between the applied force, the line displacement and the angle displacement of the mechanism was set up. And then the stiffness matrix was obtained. The six principal stiffness of the mechanism and the corresponding directions were achieved by the orthogonal transformation. The numerical calculation was performed and the results showed that the principal stiffness and directions are varied with the pose-position of the mechanism, and the principal stiffness is gradually enlarged when it is far away from the anigin. In addition, the torsion stiffness is much greater and the line deformation stiffness is smaller, the difference between the two parts is huge. The research content of this paper supplies the theoretical foundation for the further engineering design and application of the spherical parallel mechanism. 展开更多
关键词 spherical parallel mechanism static stiffness orthogonal transformation line displacement angle
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Stability of High Slope Interbedded Strata with Low Dip Angle Constituted by Soft and Hard Rock Mass
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作者 邓荣贵 周德培 张倬元 《Journal of Southwest Jiaotong University(English Edition)》 2002年第1期74-84,共11页
Slopes consisting of interbedded strata of soft and hard rock mass, such as purplish red mudstone and grey brown arkosic sandstone of Jurassic age, are very common in Sichuan basin of China. The mudstone is soft whil... Slopes consisting of interbedded strata of soft and hard rock mass, such as purplish red mudstone and grey brown arkosic sandstone of Jurassic age, are very common in Sichuan basin of China. The mudstone is soft while the sandstone is hard and contains many opening or closing joints with a high dip angle. Some are nearly parallel and the others are nearly decussated with the trend of the slopes. Many natural slopes are in deformation or sliding because of those reasons. The stability of cutting slopes and supporting method to be taken for their stability in civil engineering are important. In this paper, the stability and deformation of the slopes are studied. The methods of analysis and support design principle are analyzed also. Finally, the method put forward is applied to study Fengdian high cutting slope in Sichuan section of the express way from Chengdu to Shanghai. The results indicate that the method is effective. 展开更多
关键词 rock mass mechanics deformation and failure of high slope interbedded strata with low dip angle expressway slope
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The effect of lens parameters on the development of the primary angle-closure glaucoma
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作者 Zhaohui Feng Naixue Sun +4 位作者 Aiyi Zhou Donggang Han Yun Long Zhao Wang Xiaohua Wang 《Journal of Nanjing Medical University》 2007年第4期262-267,共6页
Objective :To investigate the role the lens dimensions played on the pathogenesis of primary angle-closure glaucoma. Methods:38 eyes of 20 patients with primary angle-closure glaucoma (PACG) and 35 eyes of 22 norm... Objective :To investigate the role the lens dimensions played on the pathogenesis of primary angle-closure glaucoma. Methods:38 eyes of 20 patients with primary angle-closure glaucoma (PACG) and 35 eyes of 22 normal individuals without ocular abnormalities were examined. The anatomical parameters of the lens and other structures of the anterior segment were calculated using B ultrasound, computer image processing and ultrasound biomicroscopy (UBM). The parameters were compared between the patients and normal subjects. Correlation analysis was used to determine the relationship between the radii of curvature of the anterior lens surface (RCALS) and the other parameters of the anterior segment. Results:Compared with the normal eyes, the eyes of PACG had thicker lens, steeper curvature of anterior lens surface, decreased depth of the anterior chamber, narrower chamber angle, and more anterior position of the ciliary bodies and lens. All these differences were significant(P 〈 0.05 or P 〈 0.01). In the PACG group, the RCALS had significantly negative correlation with the central and peripheral lens thickness (P 〈 0.01 and P 〈 0.05 respectively), and had positive correlation with relative lens position, anterior chamber depth(ACD), angle-open distance at 500 um(AOD500), trabecular iris angle (TIA) and trabecular ciliary processes distance(TCPD, P 〈 0.05 or P 〈 0.01 ). Conclusion:The occurrence of PACG is relevant to the abnormal anatomical structures of the anterior segment. Among all factors, the lens parameters play an important role in the pathogenesis. Increased lens thickness, relative more anterior position of lens, especially steepened curvature of anterior lens surface are predisposing factors of the pathologic phenomenon in PACG including pupillary blockage, shallow anterior chamber, secondary closure of chamber angle and elevation of intraocular pressure. 展开更多
关键词 primary angle-closure glaucoma lens dimensions ultrasound biomicroscope mechanism
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Influence of Structure Parameters of Double-angle Liner on Jet Formation
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作者 陈闯 王晓鸣 +2 位作者 李文彬 李伟兵 陈奎 《Defence Technology(防务技术)》 SCIE EI CAS 2012年第4期206-210,共5页
By using LS-DYNA simulation software,the influences of some structure parameters,such as top cone angle,wall thickness,liner height and height ratio of top cone,of double-angle liner on the jet formation were studied ... By using LS-DYNA simulation software,the influences of some structure parameters,such as top cone angle,wall thickness,liner height and height ratio of top cone,of double-angle liner on the jet formation were studied respectively.Their influences on jet tip velocity,tail velocity and penetration depth were revealed.The simulation results show that the formation is better if the top cone angle is selected as 28°,the wall is 2.6mm,the liner height is 140mm,and the height ratio of top cone is 60%.In large stand-off distance,the jet has a higher tip velocity,and the tip does not break.With the stand-off distance of 8 times of the charge diameter,the experiment penetrating steel target was carried out.The experiment and simulation results are in good agreement. 展开更多
关键词 弹药 应用爆炸力学 一般性问题 理论研究
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基于耗散能演化的层状黄砂岩损伤本构模型及其验证 被引量:1
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作者 刘冬桥 郭允朋 +1 位作者 李杰宇 凌凯 《工程科学学报》 EI CSCD 北大核心 2024年第5期784-799,共16页
层理构造影响工程岩体力学性质及稳定性.为探究层理倾角对岩石变形损伤过程的影响,开展了0°,15°,30°,45°,60°,75°,90°共7种不同层理角度的黄砂岩纵波波速测试和单轴压缩试验,分析了层理角度对黄砂... 层理构造影响工程岩体力学性质及稳定性.为探究层理倾角对岩石变形损伤过程的影响,开展了0°,15°,30°,45°,60°,75°,90°共7种不同层理角度的黄砂岩纵波波速测试和单轴压缩试验,分析了层理角度对黄砂岩峰值强度、弹性模量及破裂模式的影响,基于弹性模量劣化程度和耗散能演化特征分别表征黄砂岩初始层理损伤变量和荷载损伤变量,并借助Logistic函数模拟了层理与荷载耦合损伤变量演化全过程,探讨了层理角度对黄砂岩损伤演化规律的影响,进一步结合损伤力学理论与有效介质理论,建立了能够模拟单轴压缩下层状黄砂岩变形全过程的分段本构模型.结果表明:随层理倾角增大,黄砂岩纵波波速逐渐增大,峰值抗压强度和弹性模量呈现先减小后增大再减小的倒N型变化趋势,各向异性特性明显;黄砂岩破裂模式与层理倾角密切相关,倾角在0°~60°范围内时,主要发生穿切层理弱面的劈裂型张拉破坏,倾角为75°和90°时,岩样发生沿层理弱面的剪切滑移和劈裂张拉破坏;基于耗散能表征的损伤演化曲线可分为初始无损伤、损伤开始、损伤加速及损伤减速终止4个过程,借助Logistic函数构建的理论损伤模型可以很好的模拟和预测层状黄砂岩损伤演化全过程;初始层理损伤最大值与最小值之比约为1.41,表明层理倾角对黄砂岩初始损伤影响较大;建立的分段本构模型可以较好的描述层状黄砂岩单轴压缩应力–应变全过程,且理论模型曲线与试验数据吻合度高. 展开更多
关键词 岩石力学 层理倾角 能量耗散 损伤演化 本构模型
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荷载作用下多裂隙煤体力学特性与起裂角研究
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作者 王磊 商瑞豪 +5 位作者 刘怀谦 陈礼鹏 张宇 王安铖 张帅 刘化强 《岩土力学》 EI CAS CSCD 北大核心 2024年第3期659-673,共15页
为研究静态加载条件下裂隙几何位置及相互作用机制对煤体力学行为的影响,采用数字图像相关方法作为全场观测手段,以原煤预制不同位置分布下的三裂隙试样为研究对象,利用MTS816岩石伺服试验机进行单轴压缩试验,并结合颗粒流程序研究了裂... 为研究静态加载条件下裂隙几何位置及相互作用机制对煤体力学行为的影响,采用数字图像相关方法作为全场观测手段,以原煤预制不同位置分布下的三裂隙试样为研究对象,利用MTS816岩石伺服试验机进行单轴压缩试验,并结合颗粒流程序研究了裂隙不同位置分布状态下多裂隙煤体的力学特性、裂纹演化规律及破坏特征。与此同时,基于断裂力学理论讨论了T应力对煤体多裂隙尖端的影响形式及适用性。研究结果表明:当裂隙由平行共线分布向平行重叠分布过度时,煤样的宏观强度具有逐渐增强的现象;裂隙的分布形式会影响煤体的承压状态,当裂隙间距离较远时,应力场中应力薄弱区会独立存在,并随着压力增加逐渐扩展融合;而当裂隙趋于重叠分布时,应力集中区和薄弱区都会各自形成统一的受力整体,相互影响。多裂隙共线或偏置分布时,裂隙面以剪应力为主,拉应力为辅的驱动方式导致煤样发生拉剪复合破坏,而当多裂隙趋于重叠分布时,裂隙面上的剪应力转化为岩桥区拉应力,从而形成以拉应力为主导的方式驱动试样发生拉伸破坏。考虑T应力影响时,包含3个T应力分量(Tx,Ty和Txy)的起裂角理论预测值更适用于压剪应力状态下有限板多裂隙尖端裂纹扩展角度方面研究。 展开更多
关键词 多裂隙煤体 DIC技术 颗粒流模拟 断裂力学 力学特征 扩展角度
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无伴随运动2PRU-PRUR并联机构高维多目标优化设计
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作者 车林仙 彭斯洋 +3 位作者 黄鑫 何兵 贺晓辉 敖进 《机械传动》 北大核心 2024年第9期49-59,共11页
设计了一种无伴随运动的面对称一移动两转动2PRU-PRUR并联机构,应用旋量理论分析了机构自由度和运动特性。将末端执行器输出轴设置为偏置形式,可提高姿态能力。采用球面姿态角(方位角和倾摆角)描述该输出轴姿态,并推导出机构逆向位置符... 设计了一种无伴随运动的面对称一移动两转动2PRU-PRUR并联机构,应用旋量理论分析了机构自由度和运动特性。将末端执行器输出轴设置为偏置形式,可提高姿态能力。采用球面姿态角(方位角和倾摆角)描述该输出轴姿态,并推导出机构逆向位置符号解。以旋量理论为数学工具,给出局部和全域传递性能指标的定义和计算方法。在机构性能评价和工作空间分析的基础上,建立了机构尺度参数昂贵约束高维多目标优化模型,并采用多目标进化算法求解该问题。同时,为提高高维多目标优化算法在解决此模型时的性能,提出了一种矢量角高维多目标差分进化(Vector-angle-based many-objective Differential Evolution,VaDE)算法,可综合平衡个体的收敛性和分布性。应用VaDE求解机构高维多目标优化问题,得到多组Pareto备选解。研究结果可为机构尺度综合和实际应用提供参考。 展开更多
关键词 并联机构 传递性能 高维多目标优化 矢量角 差分进化算法
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