Laser Cladding of Cold-Work Tool Steel by Pulse Shaping

Repair welding of cold-work tool steels in cold is very risky and almost impossible by conventional processes. The application of pulse shaping in laser cladding with wire to avoid the solidification problems in relevant steel is demonstrated. The results show that sound remelting and/or cladding can be achieved by the right selection of laser parameters and pulse shape, i.e. long pulse duration, moderate pulse peak powers and ramped-down pulse shape. Despite the defects and softening in the cladding due to the formation of retained austenite, the cladding shows better wear resistance at lower loads compared to the heat-treated base material.     

Reflexive stability control framework for humanoid robots

In this paper we propose a general control framework for ensuring stability of humanoid robots, determined through a normalized zero-moment-point (ZMP). The proposed method is based on the modified prioritized kinematic control, which allows smooth and continuous transition between priorities. This, as long as the selected criterion is met, allows arbitrary joint movement of a robot without any regard of the consequential movement of the ZMP. On the other hand, it constrains the movement when the criterion approaches a critical condition. The critical condition thus triggers a reflexive, subconscious behavior, which has a higher priority than the desired, conscious movement. The transition between the two is smooth and reversible. Furthermore, the switching is encapsulated in a single modified prioritized task control equation. We demonstrate the properties of the algorithm on two human-inspired robots developed in our laboratory; a human-inspired leg-robot used for imitating human movement and a skiing robot.     

Mobile Domain Walls as a Bridge between Nanoscale Conductivity and Macroscopic Electromechanical Response

The interfaces in complex oxides present unique properties exploitable in nanoscale devices. Recent studies on ferroelectric BiFeO₃, BaTiO₃, and Pb(Zr,Ti)O₃ have revealed an unusually high electric conductivity of the domain walls (DWs), adding another degree of freedom for controlling the local properties of these materials. While most of the investigations are focused on thin films for nanoscale applications, many practical devices, including piezoelectric sensors, actuators, and transducers, rely on the macroscopic properties of bulk polycrystalline materials where the average effect of local properties should be small. It is shown that in polycrystalline BiFeO₃ the local domain‐wall conductivity interferes with the dynamics of the DWs within the grains, resulting in an unexpectedly large effect on the macroscopic piezoelectric response. The results thus bridge the local conductivity and the macroscopic piezoelectricity via domain‐wall dynamics, revealing that the domain‐wall conductivity must be considered when interpreting and controlling macroscopic electromechanical properties.     

Electric‐Field‐Induced Domain Switching and Domain Texture Relaxations in Bulk Bismuth Ferrite

Bismuth ferrite, BiFeO₃, is an important multiferroic material that has attracted remarkable attention for potential applications in functional devices. While thin films of BiFeO₃ are attractive for applications in nanoelectronics, bulk polycrystalline BiFeO₃ has great potential as a lead‐free and/or high‐temperature actuator material. However, the actuation mechanisms in bulk BiFeO₃ are still to be resolved. Here we report the microscopic origin of electric‐field‐induced strain in bulk BiFeO₃ ceramic by means of in situ high‐energy X‐ray diffraction. Quantification of intrinsic lattice strain and extrinsic domain switching strain from diffraction data showed that the strain response in rhombohedral bulk BiFeO₃ is primarily due to non‐180° ferroelectric domain switching, with no observable change in the phase symmetry, up to the maximum field used in the study. The origin of strain thus differs from the strain mechanism previously shown in thin film BiFeO₃, which gives a similar strain/field ratio as rhombohedral bulk BiFeO₃. A strong post‐poling relaxation of switched non‐180° ferroelectric domains has been observed and hypothesized to be due to intergranular residual stresses with a possible contribution from the conductive nature of the domain walls in BiFeO₃ ceramics.     

An adaptive IgA-BEM with hierarchical B-splines based on quasi-interpolation quadrature schemes

The isogeometric formulation of the boundary element method (IgA-BEM) is investigated within the adaptivity framework. Suitable weighted quadrature rules to evaluate integrals appearing in the Galerkin BEM formulation of 2D Laplace model problems are introduced. The proposed quadrature schemes are based on a spline quasi-interpolation (QI) operator and properly framed in the hierarchical setting. The local nature of the QI perfectly fits with hierarchical spline constructions and leads to an efficient and accurate numerical scheme. An automatic adaptive refinement strategy is driven by a residual-based error estimator. Numerical examples show that the optimal convergence rate of the Galerkin solution is recovered by the proposed adaptive method.     

Improving the multicaloric properties of Pb(Fe0.5Nb0.5)O3 by controlling the sintering conditions and doping with manganese

Designing multicaloric single-phase materials with combined electro- and magnetocaloric effects is still at its initial stage and presents a number of challenges. One of the main challenges encountered so far is to reduce the excessive electrical conductivity, which leads to the appearance of Joule heating that might completely degrade the electrocaloric response. In this work, multicaloric Pb(Fe_0.5Nb_0.5)O₃ material was successfully prepared exhibiting pronounced electrocaloric effect above room temperature and maximum magnetocaloric effect at cryogenic temperature. The conductivity was suppressed by controlling the sintering temperature. The ceramic sintered at 1000 °C exhibits maximum electrocaloric effective cooling of 0.88 °C at 28 °C and maximum magnetocaloric effect of 0.14 °C at ?271 °C. The caloric properties can be further improved by doping Pb(Fe_0.5Nb_0.5)O₃ with manganese. In comparison to the undoped sample, Pb(Fe_0.5Nb_0.5)O₃ doped with 0.5 mol% of manganese exhibits three times higher maxima of electrocaloric effective cooling (2.47 °C at 80 °C) and magnetocaloric temperature change (0.44 °C at ?271 °C).     

Nonlinear modeling of FES-supported standing-up in paraplegia for selection of feedback sensors.

This paper presents analysis of the standing-up manoeuvre in paraplegia considering the body supportive forces as a potential feedback source in functional electrical stimulation (FES)-assisted standing-up. The analysis investigates the significance of arm, feet, and seat reaction signals to the human body center-of-mass (COM) trajectory reconstruction. The standing-up behavior of eight paraplegic subjects was analyzed, measuring the motion kinematics and reaction forces to provide the data for modeling. Two nonlinear empirical modeling methods are implemented--Gaussian process (GP) priors and multilayer perceptron artificial neural networks (ANN)--and their performance in vertical and horizontal COM component reconstruction is compared. As the input, ten sensory configurations that incorporated different number of sensors were evaluated trading off the modeling performance for variables chosen and ease-of-use in everyday application. For the purpose of evaluation, the root-mean-square difference was calculated between the model output and the kinematics-based COM trajectory. Results show that the force feedback in COM assessment in FES assisted standing-up is comparable alternative to the kinematics measurement systems. It was demonstrated that the GP provided better modeling performance, at higher computational cost. Moreover, on the basis of averaged results, the use of a sensory system incorporating a six-dimensional handle force sensor and an instrumented foot insole is recommended. The configuration is practical for realization and with the GP model achieves an average accuracy of COM estimation 16+/-1.8 mm in horizontal and 39+/-3.7 mm in vertical direction. Some other configurations analyzed in the study exhibit better modeling accuracy, but are less practical for everyday usage.     

The impacts of technology on growth: Studies of agriculture and steel

Since earliest times, the human species has applied diverse types of technology. Only recently, with the application of technology on a global scale, aided by external energy, have problems of growth caused by the human transformation of earth appeared. The evidence of vigorous technological growth is ubiquitous, but this articles focuses on its driving power and energetic density as they affect agricultural fertilisers and steel production. Empirical time line patterns of development suggest two elementary growth models for projecting historical data to help answer the question of whether the unrestricted growth of consumption can be mitigated by technological development. The two examples suggest that this is not the case. The findings reveal that the increasing automation of agriculture has actually decreased overall output. The article concludes that technological applications reduce the efficiency of the system, and that technology alone cannot solve a problem that is caused by sheer quantity.