Development of interdigital transducer sensors for non-destructive characterization of thin films using high frequency Rayleigh waves

In this paper, Rayleigh waves were generated and studied over a broad frequency range (5-50 MHz) and from the dispersion phenomenon, two substrate on layer type-samples with thin layer thicknesses of 1 μm and 500 nm, respectively, were characterized. The originality in this paper is the use of surface acoustic wave interdigital transducers (IDT) to generate surface waves as well as the development of a measuring device enabling an accurate estimation of the phase velocity to be obtained, which is essential in order to characterize such thin layers. Considering the excitation frequencies (5-50 MHz) and therefore the widths necessary on the electrodes for these types of IDT sensors (20-200 μm), a lift-off procedure was chosen to deposit the electrodes on the lithium niobate (LiNbO(3)) piezoelectric substrates. The use of these IDT, first enabled problems of loss and attenuation linked to the high frequency of conventional sensors (wedge sensors) to be overcome and second to carry out quasi-monochromatic measurements in order to obtain an extremely accurate estimation of the phase velocity with rapid post-processing. An inverse method provided a very precise estimation of the thickness of the layers and the elastic constants of the substrate. The estimations of the thicknesses were then confirmed by measurements with a profilometer.     

Planning in the Real World

In this article, we describe how real world planning problems can be solved by employing Artificial Intelligence planning techniques. We introduce the paradigm of hybrid planning, which is particularly suited for applications where plans are not intended to be automatically executed by systems, but are made for humans. Hybrid planning combines hierarchical planning ?C the stepwise refinement of complex tasks ?C with explicit reasoning about causal dependencies between actions, thereby reflecting exactly the kinds of reasoning humans perform when developing plans. We show how plans are generated and how failed plans are repaired in a way that guarantees stability. Our illustrating examples are taken from a domain model for disaster relief missions enforced upon extensive floods. Finally, we present a tool to support the challenging task of constructing planning domain models. The article ends with an overview of a wide varity of actual planning applications and outlines further such in the area of cognitive technical systems.     

Translating Grafcet specifications into Mealy machines for conformance test purposes

Conformance test is a black-box test technique aiming at checking whether an implementation conforms to its specification. Numerous results have been already obtained in this field for specifications expressed in a formal language. However, these results cannot be applied for conformance test of industrial logic controllers whose specifications are given in standardized specification languages. To contribute to solve this issue, this paper proposes a method to obtain, from a Grafcet specification, an equivalent Mealy machine, without semantics loss. This method permits to describe explicitly and formally all the states and transitions that are implicitly represented in a Grafcet model.     

Performance evaluation of fixed‐bed,millistructured, and metallic foam reactor channels for CO2 methanation

Power‐to‐gas technologies, combining hydrogen produced by water electrolysis with carbon dioxide to produce substitute natural gas (SNG), can support the increased penetration of renewable electricity sources. However, the technical and economic feasibility of these technologies requires the conversion efficiency of the whole process, including the methanation step. This paper provides an experimental performance comparison of three catalytic methanation reactor concepts, a fixed‐bed reactor, a millistructured reactor, and a metallic foam reactor with the same nickel‐alumina catalyst. The response of each reactor was analyzed in light of five performance criteria, representing the methane yield, the reactor compactness, and the maximum temperature elevation. The millistructured reactor channel showed a higher methane space‐time yield and volumetric productivity than the other reactors, but a significant catalyst temperature elevation. The metallic foam reactor showed a much lower space‐time yield and volumetric productivity, but very good thermal management.

     

Structural studies of high-pressure Ba---Rh---O phases

Three different phases in the Ba---Rh---O system were prepared under high-pressure/high-temperature conditions. The black crystalline product was studied by X-ray diffraction techniques and the space groups for several phases were obtained. The first phase, the 4H polytype BaRhO₃, has already been reported in the literature, but in addition two new phases were isolated and their structures determined. The second high-pressure Ba---Rh---O product, previously reported to be an 18R polytype, was observed to be isostructural with BaIrO₃. This phase was found to be non-stoichiometric with a deficiency in rhodium in octahedral sites, with a stoichiometry of BaRh_0.92O₃. The space group is C2/m and the unit cell parameters are a = 10.005(2), b = 5.764(1), c = 14.937(3) Å, β = 102.99° and Z = 12. The third phase isolated in this study was observed to possess a hollandite-type structure with space group I2/m, where the RhO₆ octahedra share edges and vertices. Its unit cell parameters are a = 9.435(2), b = 3.1041(5), c = 10.399(2) Å, β = 94.45(1)° and Z = 1. Refinement of the structure generated the composition Ba_1.72Rh₈O₁₆.     

Visualization Support for Developing a Matrix Calculus Algorithm: A Case Study

The development of custom interactive visualization tools for specific domains and applications has been made much simpler recently by a surge of visualization tools, libraries and frameworks. Most of these tools are developed for classical data science applications, where a user is supported in analyzing measured or simulated data. But recently, there has also been an increasing interest in visual support for understanding machine learning algorithms and frameworks, especially for deep learning. Many, if not most, of the visualization support for (deep) learning addresses the developer of the learning system and not the end user (data scientist). Here we show on a specific example, namely the development of a matrix calculus algorithm, that supporting visualizations can also greatly benefit the development of algorithms in classical domains like in our case computer algebra. The idea is similar to visually supporting the understanding of learning algorithms, namely provide the developer with an interactive, visual tool that provides insights into the workings and, importantly, also into the failures of the algorithm under development. Developing visualization support for matrix calculus development went similar as the development of more traditional visual support systems for data analysts. First, we had to acquaint ourselves with the problem, its language and challenges by talking to the core developer of the matrix calculus algorithm. Once we understood the challenge, it was fairly easy to develop visual support that streamlined the development of the matrix calculus algorithm significantly.     

Direct Observation of Core–Shell Structures in Individual Lead Titanate Ferroelectric Nanostructures by Tip‐Enhanced Refractive Index Mapping

Ferroelectrics undergo a size‐driven phase transition at the nanoscale below which the spontaneous polarization, their defining property, irrevocably ceases. This threshold often referred to as the superparaelectric limit has tremendous technological relevance in an era of progressing integration. Just as the balance of short‐range elastic and long‐range electrostatic ordering in bulk, the critical size depends on temperature. Room‐temperature tip‐enhanced Raman spectroscopy (TERS) imaging of individual lead titanate (PbTiO₃) nanoislands is reported with a spatial resolution of ≈3 nm. Monitoring the spectral shift of the gold‐tip enhanced luminescence, which depends on the local refractive index, images grains composing the nanoislands. The wavelength of the enhanced luminescence shifts between the grains and their boundaries indicating the predicted core–shell structure of ferroelectric and paraelectric phase. The shear force configuration rules out the distance dependence of capacitive plasmonic coupling between tip and substrate as the origin of the observed shift. As the reported temperature‐changes in nonresonant TERS do not account for noticeable thermal effects, the underlying, even though weak, tip‐enhanced Raman spectrum of the grain core reflects PbTiO₃ close to the ferroelectric‐to‐paraelectric phase transition which is primarily related to the finite size of the grains.     

Closing ranks in rigid multi‐agent formations using edge contraction

This paper proposes a systematic approach to solve the closing rank problem for a rigid multi‐agent formation, viz. restoring rigidity after loss of an agent. The approach is based on a particular graph operation, the edge contraction operation. It is proven that when an agent is lost in an arbitrary two‐dimensional rigid formation, rigidity can always be restored by transferring all links to which this agent was incident on to one of its neighbors, though not in general any arbitrary one of them. From a graph theoretical point of view, this corresponds to contraction of a certain edge incident to the vertex representing the agent being lost. It is established, for any two‐dimensional rigid formation (graph), that there exists at least two such edges that can be contracted to solve the closing ranks problem. Later, it is demonstrated that any potential decentralized algorithm to check if an arbitrary edge is contractible would need to use information on vertices and edges that can be at arbitrarily large distance from the edge considered; and a set of rigid graph theoretical results are established for several general settings, which can be used in selection of the edge to contract in these settings in order to solve the corresponding closing ranks problems. Partial results are also obtained for three‐dimensional formations, and it is shown that the two‐dimensional results do not generalize as such to higher dimension. Copyright © 2010 John Wiley & Sons, Ltd.     

Philosophy of the M<Emphasis Type="SmallCaps">ini</Emphasis>Z<Emphasis Type="SmallCaps">inc</Emphasis> challenge

MiniZinc arose as a response to the extended discussion at CP2006 of the need for a standard modelling language for CP. This is a challenging problem, and we believe MiniZinc makes a good attempt to handle the most obvious obstacle: there are hundreds of potential global constraints, most handled by few or no systems. A standard input language for solvers gives us the capability to compare different solvers. Hence, every year since 2008 we have run the MiniZinc Challenge comparing different solvers that support MiniZinc. In this report we discuss the philosophy behind the challenge, why we do it, how we do it, and why we do it that way.