Atomistic simulation of fracture in TiAl

Atomistic simulations of fracture in L1₀ TiAl were carried out using embedded atom method (EAM) interatomic potentials and molecular statics. We studied the behavior of semi-infinite cracks under mode I loading in different orientations of the crack front and plane. For the orientation, we observed dislocation emission involving the formation of superlattice intrinsic stacking fault (SISF). For the [001](110) orientation, we observed the emission of ordinary 1/2[110] edge dislocations that were highly mobile and had a compact core. We found that cracks with [001](100) orientation cleaved near the Griffith value of loading in a purely brittle manner. Similar behavior was observed for cracks with orientation. This article is based on a presentation made in the symposium “Fundamentals of Gamma Titanium Aluminides”, presented at the TMS Annual Meeting, February 10–12, 1997, Orlando, Florida, under the auspices of the ASM/MSD Flow & Fracture and Phase Transformations Committees.     

Atomistic simulation of fracture in TiAl

Atomistic simulations of fracture in L1₀ TiA1 were carried out using embedded atom method (EAM) interatomic potentials and molecular statics. We studied the behavior of semi-infinite cracks under mode I loading in different orientations of the crack front and plane. For the (111) orientation, we observed dislocation emission involving the formation of superlattice intrinsic stacking fault (SISF). For the [001](110) orientation, we observed the emission of ordinary 1/2[110] edge dislocations that were highly mobile and had a compact core. We found that cracks with [001](100) orientation cleaved near the Griffith value of loading in a purely brittle manner. Similar behavior was observed for cracks with (100) orientation. This article is based on a presentation made in the symposium “Fundamentals of Gamma Titanium Aluminides,” presented at the TMS Annual Meeting, February 10–12, 1997, Orlando, Florida, under the auspices of the ASM/MSD Flow & Fracture and Phase Transformations Committees.     

Two-Grid Mixed Finite-Element Approximations to the Navier–Stokes Equations Based on a Newton-Type Step

A two-grid scheme to approximate the evolutionary Navier–Stokes equations is introduced and analyzed. A standard mixed finite element approximation is first obtained over a coarse mesh of size H at any positive time \(T>0\). Then, the approximation is postprocessed by means of solving a steady problem based on one step of a Newton iteration over a finer mesh of size \(h<H\). The method increases the rate of convergence of the standard Galerkin method in one unit in terms of H and equals the rate of convergence of the standard Galerkin method over the fine mesh h. However, the computational cost is essentially the cost of approaching the Navier–Stokes equations with the plain Galerkin method over the coarse mesh of size H since the cost of solving one single steady problem is negligible compared with the cost of computing the Galerkin approximation over the full time interval (0, T]. For the analysis we take into account the loss of regularity at initial time of the solution of the Navier–Stokes equations in the absence of nonlocal compatibility conditions. Some numerical experiments are shown.     

Identifikation von potenziellen Leitprozessen in Einzugsgebieten

For hazard zoning or planning of control measures the identification of the hydrogeomorphic key process is an important step to determine the recurrent design event. The present methodology for the identification of potential hydrogeomorphic key processes is a practicable tool for experts assessing homogeneous sections of running waters (torrents, mountain streams and low-lying rivers) by means of certain parameters. Filling in the developed matrix from your desk and reviewing the results with field surveys on site, the potential key process is rapidly identified for each homogeneous area, as the evaluation of 12 sample streams in Carinthia shows. Further on this method is a useful tool concerning sediment management concepts according to the National Watercourse Development Plan or financial supporting of control measures at stakeholder waters at the field of competence of the Austrian Flood Control Management.     

Design and implementation of a decision support system for competitive electricity markets

In this paper we describe software which could be used as a decision support tool for decision makers in competitive electricity markets. The tool is based on the behavior of the competitors in the market, thus many different parameters around them are considered and, additionally, many different scenarios can be used. The possible results are obtained by simulation. Two modes are implemented; one to simulate the functioning of a competitive electricity market and the other, called manual, to evaluate the success of particular strategies by a user. Finally, some computational experience is reported to validate the simulation model.     

Electronic delivery of lectures in the university environment: An empirical comparison of three delivery styles

The purpose of this study was to consider the efficacy and popularity of “Virtual Lectures” (text-based, structured electronic courseware with information presented in manageable “chunks”, interaction and multimedia) and “e-Lectures” (on-screen synchrony of PowerPoint slides and recorded voice) as alternatives to traditional lectures. We considered how three modes of delivery compare when increasingly deeper forms of learning are assessed and also student reaction to electronic delivery. Fifty-eight students in three groups took three topics of a human genetics module, one in each delivery style. Results indicated no overall greater efficacy of either delivery style when all question types were taken into account but significantly different delivery-specific results depending on which level of Bloom’s taxonomy was assessed. That is, overall, questions assessing knowledge consistently achieved the highest marks followed by analysis, comprehension, evaluation and application. Students receiving traditional lectures scored significantly lower marks for comprehension questions. Students receiving Virtual Lectures scored high for knowledge, comprehension and application but significantly lower for analysis and evaluation questions. The e-Lectures scored high for knowledge questions and were the median for all question types except application. Questionnaire analysis revealed a preference for traditional lectures over computer-based but nevertheless an appreciation of the advantages offered by them.     

Exploring Plasmonic Resonances Toward “Large-Scale” Flexible Optical Sensors with Deformation Stability

The next generation of sensors requires a simple yet compact lab on chip-based precise optical detection mechanism where data interpretation can be achieved with minimum effort. Hereby, cost-efficient strategies of manufacturing both propagating surface plasmon polariton (SPP) and localized surface plasmon resonance (LSPR) sensors on flexible platforms are explored via mechanical instabilities and oblique-angled metal evaporation. Centimeter scaled dielectric grating structures produced by plasma oxidation of pre-stressed polydimethylsiloxane film have comprised the substrates, thus imparting inherent flexibility. Subsequently, both continuous and discontinuous 1D-metallic lattices are obtained via vapor deposition of gold at different angles. The optical isotropy (gold surface-grating) and anisotropy (gold edge-grating) are distinctly observed as a difference between forward and backward diffraction efficiencies, backed by analytical correlation to the observed orders. Supported with electromagnetic modeling, the SPP and LSPR excitations are experimentally characterized under reflectance and transmittance measurements, along with a demonstration of their sensing capabilities. The LSPR supported flexible sensor provides superiority in terms of sensitivity, which is investigated under mechanical deformations to exhibit consistency of the resonant wavelength. Such consistency is strategically unraveled via “finite element method” based approaches, thus providing a new paradigm of cost-efficient, large-scaled flexible sensors.     

Coverage Path Planning with Real‐time Replanning and Surface Reconstruction for Inspection of Three‐dimensional Underwater Structures using Autonomous Underwater Vehicles

We present a novel method for planning coverage paths for inspecting complex structures on the ocean floor using an autonomous underwater vehicle (AUV). Our method initially uses a 2.5‐dimensional (2.5D) prior bathymetric map to plan a nominal coverage path that allows the AUV to pass its sensors over all points on the target area. The nominal path uses a standard mowing‐the‐lawn pattern in effectively planar regions, while in regions with substantial 3D relief it follows horizontal contours of the terrain at a given offset distance. We then go beyond previous approaches in the literature by considering the vehicle's state uncertainty rather than relying on the unrealistic assumption of an idealized path execution. Toward that end, we present a replanning algorithm based on a stochastic trajectory optimization that reshapes the nominal path to cope with the actual target structure perceived in situ. The replanning algorithm runs onboard the AUV in real time during the inspection mission, adapting the path according to the measurements provided by the vehicle's range‐sensing sonars. Furthermore, we propose a pipeline of state‐of‐the‐art surface reconstruction techniques we apply to the data acquired by the AUV to obtain 3D models of the inspected structures that show the benefits of our planning method for 3D mapping. We demonstrate the efficacy of our method in experiments at sea using the GIRONA 500 AUV, where we cover part of a breakwater structure in a harbor and an underwater boulder rising from 40 m up to 27 m depth.