scholarly journals Filtering items of mass distraction: Top-down biases against distractors are necessary for the feature-based carry-over to occur

2007 ◽  
Vol 47 (12) ◽  
pp. 1570-1583 ◽  
Author(s):  
Jason J. Braithwaite ◽  
Glyn W. Humphreys
Keyword(s):  
Top Down ◽  
2021 ◽  
Author(s):  
Davendu Y. Kulkarni ◽  
Gan Lu ◽  
Feng Wang ◽  
Luca di Mare

Abstract The gas turbine engine design involves multi-disciplinary, multi-fidelity iterative design-analysis processes. These highly intertwined processes are nowadays incorporated in automated design frameworks to facilitate high-fidelity, fully coupled, large-scale simulations. The most tedious and time-consuming step in such simulations is the construction of a common geometry database that ensures geometry consistency at every step of the design iteration, is accessible to multi-disciplinary solvers and allows system-level analysis. This paper presents a novel design-intent-driven geometry modelling environment that is based on a top-down feature-based geometry model generation method. In the proposed object-oriented environment, each feature entity possesses a separate identity, denotes an abstract geometry, and carries a set of characteristics. These geometry features are organised in a turbomachinery feature taxonomy. The engine geometry is represented by a tree-like logical structure of geometry features, wherein abstract features outline the engine architecture, while the detailed geometry is defined by lower-level features. This top-down flexible arrangement of feature-tree enables the design intent to be preserved throughout the design process, allows the design to be modified freely and supports the design intent variations to be propagated throughout the geometry automatically. The application of the proposed feature-based geometry modelling environment is demonstrated by generating a whole-engine computational geometry. This geometry modelling environment provides an efficient means of rapidly populating complex turbomachinery assemblies. The generated engine geometry is fully scalable, easily modifiable and is re-usable for generating the geometry models of new engines or their derivatives. This capability also enables fast multi-fidelity simulation and optimisation of various gas turbine systems.


Author(s):  
P. Franciosa ◽  
S. Gerbino

The need for a designer to have a tool able to do motion and constraint analysis, to check for the under-constrained and/or over-constrained status of an assembly, is strategic in a design contest where several changes are made during the design process by using CAD. Traditional kinematic tools provide little information on over-constraints at 3D level. Screw theory has been already used in mechanical assemblies, in a top-down design, to do motion and constraint analysis. This theory is here used to analyze mechanical assemblies in the contest of a feature-based CAD system. The structure of the CAD assembly is captured and described as assembly graph, similar to Datum Flow Chain, through which the motion or constraint status of any part (in terms of twist and wrench matrices), can be obtained. The underlying algorithm is based on the Kirchoff’s rules successfully applied by Davies to mechanisms. How to automatically create the assembly graph, detect the useful loops and then write the loop kinematic equations is described. Three case studies are presented related to CAD assemblies of mechanisms built up in SolidWorks® CAD system by Dassault Systemes from which assembly constraints have been acquired.


eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Samuel JD Lawrence ◽  
David G Norris ◽  
Floris P de Lange

Recent developments in human neuroimaging make it possible to non-invasively measure neural activity from different cortical layers. This can potentially reveal not only which brain areas are engaged by a task, but also how. Specifically, bottom-up and top-down responses are associated with distinct laminar profiles. Here, we measured lamina-resolved fMRI responses during a visual task designed to induce concurrent bottom-up and top-down modulations via orthogonal manipulations of stimulus contrast and feature-based attention. BOLD responses were modulated by both stimulus contrast (bottom-up) and by engaging feature-based attention (top-down). Crucially, these effects operated at different cortical depths: Bottom-up modulations were strongest in the middle cortical layer and weaker in deep and superficial layers, while top-down modulations were strongest in the superficial layers. As such, we demonstrate that laminar activity profiles can discriminate between concurrent top-down and bottom-up processing, and are diagnostic of how a brain region is activated.


2008 ◽  
Vol 28 (24) ◽  
pp. 6141-6151 ◽  
Author(s):  
T. Egner ◽  
J. M. P. Monti ◽  
E. H. Trittschuh ◽  
C. A. Wieneke ◽  
J. Hirsch ◽  
...  

Sign in / Sign up

Export Citation Format

Share Document