Process variables determining the dimensional and metallurgical properties of directionally solidified,cored turbine blades produced by investment casting of super-alloys

The investment casting process for the manufacture of directionally solidified, cored turbine blades is described. The dimensional and metallurgical properties of blades produced by this process is subject to variations which can result in long lead times in development and scrap during production. The process variables that determine the dimensional and metallurgical properties have been identified and classified in order of importance. The objective of the research is the formation of a database of process variables that can be used as a basis for control of the casting process and for predicting the final geometry as a result of the process.     

Neural network Reinforcement Learning for visual control of robot manipulators

It is known that most of the key problems in visual servo control of robots are related to the performance analysis of the system considering measurement and modeling errors. In this paper, the development and performance evaluation of a novel intelligent visual servo controller for a robot manipulator using neural network Reinforcement Learning is presented. By implementing machine learning techniques into the vision based control scheme, the robot is enabled to improve its performance online and to adapt to the changing conditions in the environment. Two different temporal difference algorithms (Q-learning and SARSA) coupled with neural networks are developed and tested through different visual control scenarios. A database of representative learning samples is employed so as to speed up the convergence of the neural network and real-time learning of robot behavior. Moreover, the visual servoing task is divided into two steps in order to ensure the visibility of the features: in the first step centering behavior of the robot is conducted using neural network Reinforcement Learning controller, while the second step involves switching control between the traditional Image Based Visual Servoing and the neural network Reinforcement Learning for enabling approaching behavior of the manipulator. The correction in robot motion is achieved with the definition of the areas of interest for the image features independently in both control steps. Various simulations are developed in order to present the robustness of the developed system regarding calibration error, modeling error, and image noise. In addition, a comparison with the traditional Image Based Visual Servoing is presented. Real world experiments on a robot manipulator with the low cost vision system demonstrate the effectiveness of the proposed approach.     

Mapping urban assemblages: the production of spatial knowledge

This paper engages with the ontology and epistemology of urban mapping. While geographical information system (GIS) and other digital technologies have long transformed the capacities for representation of urban data, this paper explores the capacity of mapping to produce new ways of seeing, understanding, planning and designing the city. With a primary focus on urban morphology, distinctions and overlaps between mapping, diagramming, planning and designing are articulated within a framework of assemblage thinking. Through cases drawn from urban design research, we analyse the mapping of political conflict, transport flows, functional mix and informal settlement. It is argued that urban mapping is a form of spatial knowledge production that is often diagrammatic, embodying a spatial logic that cannot be reduced to words and numbers. Urban mapping constructs interconnections between the ways the city is perceived, conceived and lived; and it can reveal capacities for urban transformation – the city as a space of possibility.     

Effects of Tm3+ Additions on the Crystallization of LaF3 Nanocrystals in Oxyfluoride Glasses: Optical Characterization and Up‐Conversion

The influence of the addition of 1 mol% Tm₂O₃ on the nanocrystallization of LaF₃ in a glass of composition 55SiO₂–20Al₂O₃–15Na₂O–10LaF₃ (mol%) has been studied. Tm₂O₃ affects the phase separation in the glass and delays the onset of crystallization with respect to the undoped glass. Additionally, the maximum LaF₃ crystal size is slightly greater than that in the undoped glass–ceramics. The microstructural and compositional changes in the glass matrix have been studied using several techniques, including viscosity, dilatometry, X‐ray and neutron diffraction (XRD, ND), quantitative Rietveld refinement, transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and Raman spectroscopy. Photoluminescence measurements indicate that the Tm³⁺ ions are distributed between the glassy matrix and LaF₃ crystals. Eu₂O₃ has been used as structure probe and part of the Eu³⁺ ions are reduced to Eu²⁺ when incorporated in the LaF₃ nano‐crystals. Up‐conversion spectra under IR‐excitation show a higher intensity of the blue emission in the Tm‐doped glass–ceramic compared with that in the glass.     

Synchronization of diffusively-coupled limit cycle oscillators

We develop analytical and numerical conditions to determine whether limit cycle oscillations synchronize in diffusively coupled systems. We examine two classes of systems: reaction–diffusion PDEs with Neumann boundary conditions, and compartmental ODEs, where compartments are interconnected through diffusion terms with adjacent compartments. In both cases the uncoupled dynamics are governed by a nonlinear system that admits an asymptotically stable limit cycle. We provide two-time scale averaging methods for certifying stability of spatially homogeneous time-periodic trajectories in the presence of sufficiently small or large diffusion and develop methods using the structured singular value for the case of intermediate diffusion. We highlight cases where diffusion stabilizes or destabilizes such trajectories.     

Definition of anisotropic aberrations in planar lenses

Using recently developed techniques for calculating the effective index of refraction for off-axis propagation in Ti : LiNbO3waveguides and extraordinary ray tracing in uniaxial crystals we demonstrate numerically and define anisotropic aberrations and focal lengths in planar geodesic lenses for on-axis and off-axis wave propagation.