Sliding mode control of the inchworm displacement with hysteresis compensation

This paper proposes a new modeling scheme to describe the hysteresis and the preload characteristics of piezoelectric stack actuators in the inchworm. From the analysis of piezoelectric stack actuator behavior, the hysteresis can be described by the functions of a maximum input voltage and the preload. The dynamic characteristics are also identified by the frequency domain modeling technique based on the experimental data. The hysteresis is compensated by the inverse hysteresis model for precise control of inchworm displacement. Since the dynamic stiffness of an inchworm is generally low compared to its driving condition, the mechanical vibration may degrade accuracy of the inchworm. Therefore, the SMC (Sliding Mode Control) and the Kalman filter are developed for the motion control of the inchworm. The feasibility of the proposed modeling scheme and the control algorithm is tested and verified experimentally.     

Prediction of pre- and post-peak behavior of concrete-filled circular steel tube columns under cyclic loads using fiber element method

The study of cyclic load–deformation relationships of columns in the post-peak region is essential to prevent the collapse of buildings under earthquake excitation. This paper provides an efficient method to predict the pre- and post-peak hysteretic behavior of concrete-filled circular steel tube columns under the combination of constant axial load and cyclic lateral load. A simplified nonlinear fiber element method is used to investigate uni-axial stress and strain relationship of materials in terms of the composite action between the steel tube and the concrete. The accuracy of the proposed computational technique is verified by comparing the results from this technique and experimental results.     

Configurable analogue building blocks for field-programmable analogue arrays

In this article, the design of configurable analogue blocks for field programmable analogue arrays is presented. The configurable blocks are capable of performing integration, differentiation, amplification, log, anti-log, add and negate functions. The realisation of these functions depends on differential continuous-time current-mode translinear loop techniques. To maintain high frequency operation, the programmability and configurability of the blocks are achieved by modifying the block's biasing conditions digitally. Simulation results for the presented circuits are included.     

Gradient histogram: Thresholding in a region of interest for edge detection

Selecting a threshold from the gradient histogram, a histogram of gradient magnitudes, of an image plays a crucial role in a gradient based edge detection system. This paper presents a methodology to determine the threshold from a gradient histogram generated using any kind of linear gradient operator on an image. We consider the image as a random process with dependent samples, model the gradient histogram using theories of random process and random input to a system, and determine a region of interest in the gradient histogram using certain properties of a probability density function. Standard histogram thresholding techniques are then used within the region of interest to get the threshold value. To obtain the edges, this threshold value is then used as the upper threshold of the hysteresis thresholding technique that follows the non-maximum suppression operation applied on the gradient magnitude image. The proposed methodology of determining a threshold in a gradient histogram is deduced through rigorous analysis and hence it helps in achieving consistently appreciable edge detection performance. Experimental results using different real-life and benchmark images are shown to demonstrate the effectiveness of the proposed technique.     

Computational evaluation of strain-rate-dependent deformation behavior of rubber and carbon-black-filled rubber under monotonic and cyclic straining

The molecular chain network model for elastic deformation behavior and the reptation theory for viscoelastic deformation behavior are used to derive a constitutive equation for rubber. The new eight-chain-like model contains eight standard models consisting of Langevin springs and dashpot to account for the interaction of chains with their surroundings. Monotonic and cyclic deformation behavior of rubber with relaxation under different strain rates have been examined. The results reveal the roles of the individual springs and dashpot, and the strain rate dependence of materials in the monotonic and cyclic deformation behaviors, particularly softening and hysteresis loss, that is, the Mullins effect, occurring in stress-stretch curves under cyclic deformation processes. The validity of the results is checked through comparison with experimental results. The deformation behaviors of a plane strain rubber unit cell containing carbon-black (CB) under monotonic and cyclic straining are investigated by computational simulation using the proposed constitutive equation and homogenization method. The results reveal the substantial enhancement of the resistance of CB-filled rubber to macroscopic deformation, which is caused by the marked orientation hardening due to the highly localized deformation of rubber. The role of strain rate sensitivity on such characteristic deformation behaviors as increases in the resistance to deformation, hysteresis loss, and the effects of the distribution morphology and the volume fraction of CB on the deformation behavior is clarified. The increases in the volume fraction and in the aggregation of the distribution of CB substantially raise the resistance to deformation and hysteresis loss.     

The static and fatigue strength of bolted joints in composites with hygrothermal cycling

The effects of hygrothermal cycling upon the performance of a bolted composite joint was examined. Bolt torque relaxed as the number of environmental cycles increased. Comparison with analytical results suggested that the bolt torque “zigzag” behavior probably results from the natural sensitivity of bolted composite joints to the existing ambient temperature and moisture. The washer effect and specimen surface finishes were investigated to study the friction effect on joint bearing performance. Fatigue tests of specimens exposed to hygrothermal cycling exhibited greater hole elongation than specimens not exposed. High preload does improve static failure strength and the fatigue life of specimens under room conditions. Tests run on IM6/3501-6 material specimens with hygrothermal cycling show reasonable declines in fatigue life. The moisture weight gains of composites under hygrothermal cycling exposure were measured and compared to numerical results; good correlation was obtained. As a result, bolt failure occurred in some fatigue tests and is most frequently associated with large thickness-to-diameter ratio. The peak-to-peak stress was defined to study the effect of the R-ratio on bolts for the bolt failure problem.     

RNA Relics and Origin of Life

A number of small RNA sequences, located in different non-coding sequences and highly preserved across the tree of life, have been suggested to be molecular fossils, of ancient (and possibly primordial) origin. On the other hand, recent years have revealed the existence of ubiquitous roles for small RNA sequences in modern organisms, in functions ranging from cell regulation to antiviral activity. We propose that a single thread can be followed from the beginning of life in RNA structures selected only for stability reasons through the RNA relics and up to the current coevolution of RNA sequences; such an understanding would shed light both on the history and on the present development of the RNA machinery and interactions. After presenting the evidence (by comparing their sequences) that points toward a common thread, we discuss a scenario of genome coevolution (with emphasis on viral infectious processes) and finally propose a plan for the reevaluation of the stereochemical theory of the genetic code; we claim that it may still be relevant, and not only for understanding the origin of life, but also for a comprehensive picture of regulation in present-day cells.     

Effect of Ba(Zn1/3Nb2/3)O3 modification on structure and ferroelectric properties of 0.6Pb(Mg1/3Nb2/3)O3–0.4Pb(Zr0.52Ti0.48)O3 ceramics

In this study, (1−x)[0.6Pb(Mg_1/3Nb_2/3)O₃–0.4Pb(Zr_0.52Ti_0.48)O₃]–xBa(Zn_1/3Nb_2/3)O₃; (1−x)PMNZT60/40–xBZN having x=0, 2.5, 5, 7.5, and 10 mol% ceramics were prepared by mixed oxide powder method and sintered using a two-step process. Phase transitions were investigated by XRD, microstructure by SEM, crystal morphology by TEM, the dielectric and ferroelectric properties by capacitance measurement setup and modified Sawyer-Tower circuit, respectively. The dielectric constant and dielectric loss tangent were measured as functions of both temperature and frequency. The XRD results show the phase transition from tetragonal phase to pseudo-cubic phase with addition of BZN in PMNZT system. Grain size of about 1.23–2.42 μm and crystallite size in a range of 421–2152 nm were obtained. The pure-phase 0.6PMN–0.4PZT ceramics show the normal ferroelectric behavior. The 0.95(PMNZT60/40)–0.05BZN and 0.925(PMNZT60/40)–0.075BZN showed a broad and diffused dielectric properties and the dispersive phase transition, indicating the relaxor ferroelectric behavior. The transition temperature in the BZN-modified PMNZT system is seen to decrease from 166 °C in pure PMNZT60/40 to 102 °C and 54 °C with increasing BZN content to 5 and 10 mol%, respectively. In addition, the maximum dielectric constant is decreased with increasing BZN content. The P–E hysteresis loop measurements show the change from the normal ferroelectric behavior in PMNZT60/40 ceramic to more relaxor behavior that was induced with BZN addition. These results clearly demonstrated the significance of BZN to the electrical responses of the PMNZT60/40 system.     

The effect of stiffeners on the strain patterns of the welded connection zone

The behavior of the welded I-beams to box-columns connections is investigated both experimentally and numerically to identify the effects of stiffeners and column flange thickness on the energy dissipation characteristic of the connection. Numerical test specimens were developed and analyzed by the finite element method and the results were compared with full-scale experiments. The effects of various stiffeners such as, column stiffeners, side-stiffeners, and top-flange, and bottom-flange stiffeners were investigated. The contribution of each stiffener in controlling the location of the plastic deformation and the energy dissipation in the connection zone were examined.     

考虑碰撞挤压的螺栓接头迟滞回线建模

在振动、冲击载荷作用下,螺栓连接结构呈现出明显的非线性迟滞现象,影响结构的整体性能。传统的动力学研究仅考虑连接界面的微观/宏观滑移,很少研究螺栓杆与孔壁之间由于界面滑移产生的接触力。基于BRAKE的RIPP模型,提出一种考虑能量损耗的“钉扎接触力”模型,以实现对切向力3个阶段的整体迟滞回线建模;基于该模型,分析预紧力以及摩擦因数对迟滞回线的影响。提出的模型与现有的研究结果吻合性良好,验证了整体迟滞模型的有效性。研究表明：摩擦因数和预紧力的增加会扩大迟滞回线所包围的面积,进而导致单个周期内切向滑移所造成的能量损耗逐渐增加;相比于摩擦因数,预紧力对微滑移阶段的迟滞特性影响更为明显。提出的模型可以反映出“钉扎”接触过程对迟滞特性的影响,有助于更好地揭示螺栓连接在冲击载荷下的响应特征及其非线性行为,为后续螺栓连接结构动力学建模提供帮助。