Dimensional Synthesis for 3-PRS Mechanism Based on Identifiability Performance

Many performance indices for parallel mechanism are put forward in the phase of dimensional synthesis,except for identifiability index,which determines the difficulty of kinematical calibration.If the dimensional parameters are inappropriately selected,the existing methods for optimizing identifiability will not effectively work.Thus,with the aim of studying identifiability optimization in dimensional synthesis for 3-PRS mechanism,kinematics with structural errors is analyzed to provide theoretical bases for kinematical model.Then through a comparison of two 3-PRS mechanisms with different dimensional parameters,identifiability performance is proved to be necessary and feasible for optimization in the phase of dimensional design.Finally,an index δ is proposed to scale the identifiability performance.With the index,identifiability analysis and dimensional synthesis simulation in the whole workspace is completed.The index is verified to be correct and feasible,and based on the index,a procedure of dimensional synthesis,as well as an example set of non-dimensional parameters of 3-PRS mechanism,is proposed.The proposed identifiability index and design method can effectively introduce identifiability optimization into dimensional synthesis,and will obviously benefit later kinematical calibration.

Mechanism Modeling and Simulation Based on Dimensional Deviation

To analyze the effects on motion characteristics of mechanisms of dimensional variations, a study on random dimensional deviation generation techniques for 3D models on the basis of the present mechanical modeling software was carried out, which utilized the redeveloped interfaces provided by the modeling software to develop a random dimensional deviation generation system with certain probability distribution characteristics. This system has been used to perform modeling and simulation of the specific mechanical time delayed mechanism under multiple deviation varieties, simulation results indicate the dynamic characteristics of the mechanism are influenced significantly by the dimensional deviation in the tolerance distribution range, which should be emphasized in the design.

Recognition of an additional mechanism leading to myocardial abnormalities

A growing body of evidence explicitly suggests the significant role of inflammatory processes in the development and progressive deterioration of vascular diseases and cardiomyopathies.1-3 In recent years, a large variety of infections have been reported to be associated with the development of cardiomyopathy; the pathogenic factors include rickets, bacteria, protozoa and other parasites,and also, at least 17 viruses.2。

Mechanisms and Processes Leading to Reverse Zoning in the Andong Granitoid Pluton, Andong Batholith, Korea

The Andong pluton consists of comagmatic granitoid rocks which constitute outstanding examples of reversely zoned granitoids. The pluton has three lithofacies: hornblende biotite tonalite, biotite granodiorite and porphyritic biotite granite. The zoned pattern forms by locating a tonalite core containing high-temperature mafic assemblages in central part,granodiorite rims in marginal part, and a porphyritic granite cap containing more felsic assemblages in topside of the pluton.Mineral abundances as well as bulk compositions of the granitoids indicate that the interior is enriched in mafic minerals and that it shows higher contents of oxides than the margin and topside. The compositional gradients change gradually with continuity between the lithofacies. The regular compositional variations within the pluton support the argument that the pluton behaved as an individual petrochemical system. Model abundances of the granitoids are in agreement with the bulk compositional gradients, suggesting that no significant interaction with country rocks occurred. Remobilization (resurgence) of deeper parts of the system into the more felsic magmas of the chamber explains the reverse zoning. Fractional crystallization was of importance and probably accounts for the selective removal of the settling phases. The Andong pluton is an example of reversely zoned plutons related by remobilization of more mafic but consanguineous magmas. Large-scale upwelling occurred in the pluton leading to the present arrangement of three lithofacies. It is conceivable that remnants of the reverse zoning become more difficult to discern as the plutonic rocks reach the latest stages of their evolution. In this case, the Andong pluton represents an earlier stage in the evolution of a felsic system that is usually represented by the final stages in normally zoned plutons.

Leading-edge receptivity of boundary layer to three-dimensional free-stream turbulence

The laminar-turbulent transition has always been a hot topic of fluid mechanics. Receptivity is the initial stage and plays a crucial role in the entire transition process. The previous studies of receptivity focus on external disturbances such as sound waves and vortices in the free stream, whereas those on the leading-edge receptivity to the three-dimensional free-stream turbulence (FST), which is more general in the nature, are rarely reported. In consideration of this, this work is devoted to investigating the receptivity process of three-dimensional Tollmien-Schlichting (T-S) wave packets excited by the three-dimensional FST in a flat-plate boundary layer numerically. The relations between the leading-edge receptivity and the turbulence intensity are established, and the influence of the FST directions on the propagation directions and group velocities of the excited T-S wave packets is studied. Moreover, the leading-edge receptivity to the anisotropic FST is also studied. This parametric investigation can contribute to the prediction of laminar-turbulent transition.

Degradation mechanism of two-dimensional electron gas density in high Al-content AlGaN/GaN heterostructures

This paper finds that the two-dimensional electron gas density in high Al-content A1GaN/GaN heterostructures exhibits an obvious time-dependent degradation after the epitaxial growth. The degradation mechanism was investigated in depth using Hall effect measurements,high resolution x-ray diffraction,scanning electron microscopy,x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy.The results reveal that the formation of surface oxide is the main reason for the degradation,and the surface oxidation always occurs within the surface hexagonal defects for high Al-content AlGaN/GaN heterostructures.

Fabrication and formation mechanism of NbC_x-C three-dimensional netted fibers

Micrometer NbC_x-C three-dimensional netted fibers were synthesized by thecarbothermal method under 0.1 MPa of N_2 ambient atmosphere at a relatively low temperature. Rawmaterials were commercial powders of Nb_2O_5 (99.95 percent), reactive carbon (99.99 percent), NaCl(99.95 percent) and sucrose (99.94 percent). The relationship of the fabrication processing with thecomposition, crystal structure and morphology of fibers was investigated. The formation mechanismwas also proposed and discussed.

Macro-micro behaviors and failure mechanism of frozen weakly cemented mudstone

Understanding the mechanical properties and multiscale failure mechanism of frozen soft rock is an important prerequisite for the construction safety of tunnels,artificially frozen ground and other infrastructure in cold regions.In this study,the triaxial compression test are performed on mudstone in the weakly cemented soft rock strata in the mining area of western China,and the mechanical characteristics and failure mechanism of weakly cemented mudstone are systematically investigated under the combined action of freezing and loading.Furthermore,the quantitative relationship between the microstructural parameters and the macroscopic strength and deformation parameters is established based on fractal theory.Thus,the failure mechanism of frozen weakly cemented mudstone is revealed on both micro- and macro-scales.The results show that temperature and confining pressure significantly affects the elastic modulus and peak strength of weakly cemented mudstone.With decreasing temperature,the compressive strength increases,while the corresponding peak strain decreases gradually.On the deformation curve,the plastic deformation stage is shortened,and the brittle fracture feature at the post-peak stage is more prominent,and the elastic modulus correspondingly increases with decreasing temperature.Under low-temperature conditions,most of the weakly cemented mudstone undergoes microscopic shear failure along the main fracture surface.The micro-fracture morphology characteristics of weakly cemented mudstone under different temperatures are quantified via the fractal dimension,and an approximately exponential relationship can be obtained among the fractal dimension and the temperature,compressive strength and elastic modulus.

Impacts of freezing and thermal treatments on dimensional and mechanical properties of wood flour-HDPE composite

Wood plastic composite （WPC） of wood flour （WF）, high density polyethylene （HDPE）, maleic anhydride-grafted polyethylene （MAPE） and lubricant was prepared by extrusion, and then exposed to different temperatures to evaluate the effects of freezing and thermal treatment on its dimensional and mechanical properties. At elevated temperatures, WPC expanded rapidly initially, and then contracted slowly until reaching an equilibrium state. Treatment at 52°C and relative humidity of 50% for 16 days improved the mechanical properties of WPC： flexure, tensile strength, and izod unnotched impact strength increased by 8%, 10% and 15%, respectively. Wide-angle X-ray diffraction （XRD） tests showed that the degree of crystalization of HDPE in WPC declined with increasing treatment temperature.

Diagrammatic Approach for Investigating Two Dimensional Elastic Collisions in Momentum Space I: Newtonian Mechanics

We present the usefulness of the diagrammatic approach for analyzing two dimensional elastic collision in momentum space. In the mechanics course, we have two major purposes of studying the collision problems. One is that we have to obtain velocities of the two particles after the collision from initial velocities by using conservation laws of momentum and energy. The other is that we have to study two ways of looking collisions, i.e. laboratory system and center-of-mass system. For those two major purposes, we propose the diagrammatic technique. We draw two circles. One is for the center-of-mass system and the other is for the laboratory system. Drawing these two circles accomplish two major purposes. This diagrammatic technique can help us understand the collision problems quantitatively and qualitatively.

A general solution for one dimensional chemo-mechanical coupled hydrogel rod

Smart hydrogels are environmentally sensitive hydrogels, which can produce a sensitive response to external stimuli, and often exhibit the characteristics of multi filed coupling. In this paper, a hydrogel rod under chemomechanical coupling was analytically studied based on a poroelastical model. The already known constitutive and governing equations were simplified into the one dimensional case, then two different boundary conditions were considered. The expressions of concentration, displacement,chemical potential and stress related to time were obtained in a series form. Examples illustrate the interaction mechanism of chemical and mechanical effect. It was found that there was a balance state in the diffusion of concentration and the diffusion process could lead to the expansion or the stress change of the hydrogel rod.

Origin of Luminescent Centers and Edge States in Low-Dimensional Lead Halide Perovskites:Controversies,Challenges and Instructive Approaches

With only a few deep-level defect states having a high formation energy and dominance of shallow carrier non-trapping defects,the defect-tolerant electronic and optical properties of lead halide perovskites have made them appealing materials for high-efficiency,low-cost,solar cells and light-emitting devices.As such,recent observations of apparently deep-level and highly luminescent states in low-dimensional perovskites have attracted enormous attention as well as intensive debates.The observed green emission in 2D CsPb2Br5 and 0 D Cs4PbBr6 poses an enigma over whether it is originated from intrinsic point defects or simply from highly luminescent CsPbBr3 nanocrystals embedded in the otherwise transparent wide band gap semiconductors.The nature of deep-level edge emission in 2D Ruddlesden–Popper perovskites is also not well understood.In this mini review,the experimental evidences that support the opposing interpretations are analyzed,and challenges and root causes forthe controversy are discussed.Shortcomings in the current density functional theory approaches to modeling of properties and intrinsic point defects in lead halide perovskites are also noted.Selected experimental approaches are suggested to better correlate property with structure of a material and help resolve the controversies.Understanding and identification of the origin of luminescent centers will help design and engineer perovskites for wide device applications.

Removal Mechanism of Aqueous Lead by a Novel Eco-material: Carbonate Hydroxyapatite

Kinetics and mechanisms on the removal of aqueous lead ion by carbonate hydroxyapatite （CHap） are investigated in the present work. Experimental results show that, in the whole pH range, the lead removal percentage increases with decreasing pH values and reaches a maximum at pH=2-3. Under some conditions, the lead residual concentration is below national integrated wastewater discharge standard, even drinking water standard. The removal behavior is a complicated non-homogeneous solid/liquid reaction, which can be described by two stages from kinetic point of view. At the earlier stage, reaction rate is so fast that its kinetic course is intricate, which requires further study. At the latter stage, the rate of reaction becomes slow and the process of reaction accords with one order reaction kinetic equation. Experimental results show that the relationship between reaction rate constant k1 and temperature T accords to Arrhenius Equation, and the activation energy of sorption （Ea） is 11.93 kJ/mol and frequency factor （A） is 2.51 s^-1. X-ray diffraction （XRD）, scanning electron microscopy with an energy dispersive X-ray fluoresence spectrometer （SEM-EDS） and toxicity characteristic leaching procedure （TCLP） test were conducted in this work. It is indicated that the main mechanism is dissolution-precipitation, accompanying with superficial sorption.

Three-dimensional cellular automata based particle flow simulations of mechanical properties of talus deposit

Based on three-dimensional cellular automata （CA）, a new stochastic simulation model to simulate the microstructures and particle flow of talus deposit is proposed. Ill addition, an auto-modeling program CARS is developed, with which nunaerical simulations can be conducted conveniently. For the problem of simulating mechanical behaviors of talus deposit, spatial anangement or sphere shapes should be considered. In the new modeling method, four sphere anangement models are developed for the particle flow simulation of talus deposit. Numerical results show that the talus deposit has the mechanical characteristics of typical stress-strain curves, as other rock-like materials. The cohesion of talus deposit decreases with increasing rock content, while the internal friction angle increases with increasing rock contents. Finally, numerical simulation is verified with the results of field test.

Dimensional and Mechanical Similarity Analysis of the Flow in Rotating Liquid Film Reactor

A rotating liquid film reactor (RLFR) is a device of two coaxial rotating conical cylinders with the inner cone rotating and the outer one stationary. A complete mathematical model for the flow between the conical cylinders is built and a dimensional analysis is carried out. It is proved that at each point of the flow field the dimensionless pressure and velocity of the flow are determined by parameters: Reynolds number (Re), aspect ratio (Γ), radius ratio (η) and wall inclination angle (α). Furthermore, a sufficient and a necessary condition are derived from mechanical similarity between RLFR and a manufacturing equipment geometrically similar to RLFR. Finally, a numerical simulation for the distribution of pressure and velocity is performed. The results may provide a theoretical basis for experiment method and numerical simulation of the flow in a RLFR-like device.

A Study on Dimension Synthesis for the Peaucellier Mechanism

Straight-line motion, albeit simple, manifests itself in numerous applications, from running steam engines and oil wells to manufacturing parts with straight edges and sides. The drive to maximize production creates a need for continuously running assembly-line manufacturing comprised of precise, individually optimized components. While there are many so-called straight-line generating mechanisms, few actually produces a true straight-line, most generate only approximate straight-line. Featured an eight-link rhomboidal system with length constraints,, the Peaucellier mechanism is one that actually produces a true straight line intrinsically. This paper presents a study on the dimension synthesis of the Peaucellier mechanism, namely by identifying the correct ratio of linkage lengths to produce the longest straight line stroke. In addition to designing for stroke, another objective of interest is to attain a desired velocity profile along the path. Kinematic analysis of the velocity profile on the mechanism will render the creation of input angular velocity standards based on desired stroke speed. Given the stroke and velocity specifications, specific steps to size the dimensions of the mechanism developed as result of this study will be presented.

COMPUTER SIMULATION OF 3-DIMENSIONAL DYNAMIC ASSEMBLY PROCESS OF MECHANICAL ROTATIONAL BODY

Focusing on the study of the components of mechanical rotational body,the data structure and algorithm of component model generation are discussed.Some problems in assembly process of 3 dimensional graph of components are studied in great detail.

Optimal Design of a Main Driving Mechanism for Servo Punch Press Based on Performance Atlases

The servomotor drive turret punch press is attracting more attentions and being developed more intensively due to the advantages of high speed,high accuracy,high flexibility,high productivity,low noise,cleaning and energy saving.To effectively improve the performance and lower the cost,it is necessary to develop new mechanisms and establish corresponding optimal design method with uniform performance indices.A new patented main driving mechanism and a new optimal design method are proposed.In the optimal design,the performance indices,i.e.,the local motion/force transmission indices ITI,OTI,good transmission workspace good transmission workspace(GTW) and the global transmission indices GTIs are defined.The non-dimensional normalization method is used to get all feasible solutions in dimensional synthesis.Thereafter,the performance atlases,which can present all possible design solutions,are depicted.As a result,the feasible solution of the mechanism with good motion/force transmission performance is obtained.And the solution can be flexibly adjusted by designer according to the practical design requirements.The proposed mechanism is original,and the presented design method provides a feasible solution to the optimal design of the main driving mechanism for servo punch press.

Design of Vegetable Pot Seedling Pick‑up Mechanism with Planetary Gear Train

It has been challenging to design seedling pick-up mechanism based on given key points and trajectories,because it involves dimensional synthesis and rod length optimization.In this paper,the dimensional synthesis of seedling pickup mechanism with planetary gear train was studied based on the data of given key points and the trajectory of the endpoint of seedling pick-up mechanism.Given the positions and orientations requirements of the five key points,the study first conducted a dimensional synthesis of the linkage size and center of rotation.The next steps were to select a reasonable solution and optimize the data values based on the ideal seedling trajectory.The link motion was driven by the planetary gear train of the two-stage gear.Four pitch curves of noncircular gears were obtained by calculating and distributing the transmission ratio according to the data.For the pitch curve with two convex points,the tooth profile design method of incomplete noncircular gear was applied.The seedling pick-up mechanism was tested by a virtual prototype and a physical prototype designed with the obtained parameter values.The results were consistent with the theoretical design requirements,confirming that the mechanism meets the expected requirements for picking seedlings up.This paper presents a new design method of vegetable pot seedling pick-up mechanism for an automatic vegetable transplanter.

The rock breaking and ROP increase mechanisms for single-tooth torsional impact cutting using DEM

Torsional impact drilling is a new technology which has the advantages of high rock-breaking efficiency and a high rate of penetration(ROP).So far,there is no in-depth understanding of the rock-breaking mechanism for the ROP increase from torsional impact tools.Therefore,it has practical engineering significance to study the rock-breaking mechanism of torsional impact.In this paper,discrete element method(DEM)software(PFC2 D)is used to compare granite breaking under the steady and torsional impacting conditions.Meanwhile,the energy consumption to break rock,microscopic crushing process and chip characteristics as well as the relationship among these three factors for granite under different impacting frequencies and amplitudes are discussed.It is found that the average cutting force is smaller in the case of torsional impact cutting(TIC)than that in the case of steady loading.The mechanical specific energy(MSE)and the ratio of brittle energy consumption to total energy are negatively correlated;rock-breaking efficiency is related to the mode of action between the cutting tooth and rock.Furthermore,the ROP increase mechanism of torsional impact drilling technology is that the ratio of brittle energy consumption under the TIC condition is larger than that under a steady load;the degree of repeated fragmentation of rock chips under the TIC condition is lower than that under the steady load,and the TIC load promotes the formation of a transverse cracking network near the free surface and inhibits the formation of a deep longitudinal cracking network.