8,394 research outputs found
Developing student spatial ability with 3D software applications
This paper reports on the design of a library of software applications for the teaching and learning of spatial geometry and visual thinking. The core objective of these applications is the development of a set of dynamic microworlds, which enables (i) students to construct, observe and manipulate configurations in space, (ii) students to study different solids and relates them to their corresponding nets, and (iii) students to promote their visualization skills through the process of constructing dynamic visual images. During the developmental process of software applications the key elements of spatial ability and visualization (mental images, external representations, processes, and abilities of visualization) are carefully taken into consideration
Analysis of swirling flow in hydrocyclones operating under dense regime
There are many circumstances where hydrocyclone performance and dense flow are intertwined, such as for example when feed solids flow exceeds hydrocyclone capacity during continuous operations. The work reported here, which is part of an ongoing research effort to develop a robust CFD model for prediction of hydrocyclone performance, focuses on hydrocyclone operation under high solids concentration. The paper presents the basic physics framework that accounts for solid–liquid and solid–solid interactions under hydrocyclone’s swirling flow. Operating conditions that are past the transition from spray to rope regime are deliberately chosen for this purpose. Model predictions are validated by comparison with solids split and separation curves measured on a 100 mm diameter hydrocyclone. CFD model predictions permit taking an insightful look at the inside of a hydrocyclone under extreme operating conditions, which would be difficult to achieve experimentally. Velocity profiles, G-force distribution and distribution of solids predicted by CFD are bound to lead to a better understanding of the separation that takes place inside a hydrocyclone, which may eventually help improve hydrocyclone design and performance
Exploratory Experimentation of Three Techniques for Rotating a 3D Scene by Primary School Students
International audienceMulti-touch mobile devices are now commonly used in any area, including education. In this context we focus on applications for 3D geometry learning in primary schools. Manipulating a 3D scene based on a 2D input touch space is one key challenge of such applications for pupils. In this paper we present the results of an exploratory experimentation with pupils. We compare three different interaction techniques for rotating a 3D scene based on different interaction metaphors by using: multi-touch input, movements of the tablet captured with a gyroscope sensor and movements of the head captured by a camera-based head tracking. We ran the exploratory experiment with 28 pupils in a primary school to compare these three techniques by considering the performance and the subjective preferences. Results indicate worst performance for head-tracking and similar performance for multi-touch input and gyroscope-based movement. Qualitative results indicate participant preference for multi-touch interaction
Unwind: Interactive Fish Straightening
The ScanAllFish project is a large-scale effort to scan all the world's
33,100 known species of fishes. It has already generated thousands of
volumetric CT scans of fish species which are available on open access
platforms such as the Open Science Framework. To achieve a scanning rate
required for a project of this magnitude, many specimens are grouped together
into a single tube and scanned all at once. The resulting data contain many
fish which are often bent and twisted to fit into the scanner. Our system,
Unwind, is a novel interactive visualization and processing tool which
extracts, unbends, and untwists volumetric images of fish with minimal user
interaction. Our approach enables scientists to interactively unwarp these
volumes to remove the undesired torque and bending using a piecewise-linear
skeleton extracted by averaging isosurfaces of a harmonic function connecting
the head and tail of each fish. The result is a volumetric dataset of a
individual, straight fish in a canonical pose defined by the marine biologist
expert user. We have developed Unwind in collaboration with a team of marine
biologists: Our system has been deployed in their labs, and is presently being
used for dataset construction, biomechanical analysis, and the generation of
figures for scientific publication
A standard format and a graphical user interface for spin system specification
We introduce a simple and general XML format for spin system description that
is the result of extensive consultations within Magnetic Resonance community
and unifies under one roof all major existing spin interaction specification
conventions. The format is human-readable, easy to edit and easy to parse using
standard XML libraries. We also describe a graphical user interface that was
designed to facilitate construction and visualization of complicated spin
systems. The interface is capable of generating input files for several popular
spin dynamics simulation packages.Comment: Submitted for publicatio
Transforming mesoscale granular plasticity through particle shape
When an amorphous material is strained beyond the point of yielding it enters
a state of continual reconfiguration via dissipative, avalanche-like slip
events that relieve built-up local stress. However, how the statistics of such
events depend on local interactions among the constituent units remains
debated. To address this we perform experiments on granular material in which
we use particle shape to vary the interactions systematically. Granular
material, confined under constant pressure boundary conditions, is uniaxially
compressed while stress is measured and internal rearrangements are imaged with
x-rays. We introduce volatility, a quantity from economic theory, as a powerful
new tool to quantify the magnitude of stress fluctuations, finding systematic,
shape-dependent trends. For all 22 investigated shapes the magnitude of
relaxation events is well-fit by a truncated power law distribution , as has been proposed within the context of plasticity
models. The power law exponent for all shapes tested clusters around
1.5, within experimental uncertainty covering the range 1.3 - 1.7. The
shape independence of and its compatibility with mean field models
indicate that the granularity of the system, but not particle shape, modifies
the stress redistribution after a slip event away from that of continuum
elasticity. Meanwhile, the characteristic maximum event size changes by
two orders of magnitude and tracks the shape dependence of volatility. Particle
shape in granular materials is therefore a powerful new factor influencing the
distance at which an amorphous system operates from scale-free criticality.
These experimental results are not captured by current models and suggest a
need to reexamine the mechanisms driving mesoscale plastic deformation in
amorphous systems.Comment: 11 pages, 8 figures. v3 adds a new appendix and figure about event
rates and changes several parts the tex
Stiffness pathologies in discrete granular systems: bifurcation, neutral equilibrium, and instability in the presence of kinematic constraints
The paper develops the stiffness relationship between the movements and
forces among a system of discrete interacting grains. The approach is similar
to that used in structural analysis, but the stiffness matrix of granular
material is inherently non-symmetric because of the geometrics of particle
interactions and of the frictional behavior of the contacts. Internal geometric
constraints are imposed by the particles' shapes, in particular, by the surface
curvatures of the particles at their points of contact. Moreover, the stiffness
relationship is incrementally non-linear, and even small assemblies require the
analysis of multiple stiffness branches, with each branch region being a
pointed convex cone in displacement-space. These aspects of the particle-level
stiffness relationship gives rise to three types of micro-scale failure:
neutral equilibrium, bifurcation and path instability, and instability of
equilibrium. These three pathologies are defined in the context of four types
of displacement constraints, which can be readily analyzed with certain
generalized inverses. That is, instability and non-uniqueness are investigated
in the presence of kinematic constraints. Bifurcation paths can be either
stable or unstable, as determined with the Hill-Bazant-Petryk criterion.
Examples of simple granular systems of three, sixteen, and sixty four disks are
analyzed. With each system, multiple contacts were assumed to be at the
friction limit. Even with these small systems, micro-scale failure is expressed
in many different forms, with some systems having hundreds of micro-scale
failure modes. The examples suggest that micro-scale failure is pervasive
within granular materials, with particle arrangements being in a nearly
continual state of instability
Plasticity size effects in tension and compression of single crystals
The effect of size and loading conditions on the tension and compression stress–strain response of micron-sized planar crystals is investigated using discrete dislocation plasticity. The crystals are taken to have a single active slip system and both small-strain and finite-strain analyses are carried out. When rotation of the tensile axis is constrained, the build-up of geometrically necessary dislocations results in a weak size dependence but a strong Bauschinger effect. On the other hand, when rotation of the tensile axis is unconstrained, there is a strong size dependence, with the flow strength increasing with decreasing specimen size, and a negligible Bauschinger effect. Below a certain specimen size, the flow strength of the crystals is set by the nucleation strength of the initially present Frank–Read sources. The main features of the size dependence are the same for the small-strain and finite-strain analyses. However, the predicted hardening rates differ and the finite-strain analyses give rise to some tension–compression asymmetry.
- …