10,572 research outputs found
Multiscale analysis of re-entrant production lines: An equation-free approach
The computer-assisted modeling of re-entrant production lines, and, in
particular, simulation scalability, is attracting a lot of attention due to the
importance of such lines in semiconductor manufacturing. Re-entrant flows lead
to competition for processing capacity among the items produced, which
significantly impacts their throughput time (TPT). Such production models
naturally exhibit two time scales: a short one, characteristic of single items
processed through individual machines, and a longer one, characteristic of the
response time of the entire factory. Coarse-grained partial differential
equations for the spatio-temporal evolution of a "phase density" were obtained
through a kinetic theory approach in Armbruster et al. [2]. We take advantage
of the time scale separation to directly solve such coarse-grained equations,
even when we cannot derive them explicitly, through an equation-free
computational approach. Short bursts of appropriately initialized stochastic
fine-scale simulation are used to perform coarse projective integration on the
phase density. The key step in this process is lifting: the construction of
fine-scale, discrete realizations consistent with a given coarse-grained phase
density field. We achieve this through computational evaluation of conditional
distributions of a "phase velocity" at the limit of large item influxes.Comment: 14 pages, 17 figure
PC-based aviation training devices (PCATDs): research, development and certification
This paper examines the development of two PCATD’s (one
helicopter, one fixed-wing) and their eventual certification by CAA.
Certification has demonstrated the potential these devices have for aviation
training in New Zealand. Traditionally FTD‘s and PCATD’s have been
sourced from foreign companies, and they represent a considerable financial
investment for large flying training organisations. The procurement of these
simulator types is generally beyond the financial resources of most small to
medium sized flying schools. Aviation training in NZ is facing significant
financial constraints as well as an increasing demand to simulate complex
glass cockpit systems that are now installed in most new General Aviation
(GA) aircraft. The development, utilisation and certification of this type of
PCATD technology could solve these difficult challenges
Evaluation of ADAM/1 model for advanced coal extraction concepts
Several existing computer programs for estimating life cycle cost of mining systems were evaluated. A commercially available program, ADAM/1 was found to be satisfactory in relation to the needs of the advanced coal extraction project. Two test cases were run to confirm the ability of the program to handle nonconventional mining equipment and procedures. The results were satisfactory. The model, therefore, is recommended to the project team for evaluation of their conceptual designs
Simulation modelling and visualisation: toolkits for building artificial worlds
Simulations users at all levels make heavy use of compute resources to drive computational
simulations for greatly varying applications areas of research using different simulation
paradigms. Simulations are implemented in many software forms, ranging from highly standardised
and general models that run in proprietary software packages to ad hoc hand-crafted
simulations codes for very specific applications. Visualisation of the workings or results of a
simulation is another highly valuable capability for simulation developers and practitioners.
There are many different software libraries and methods available for creating a visualisation
layer for simulations, and it is often a difficult and time-consuming process to assemble a
toolkit of these libraries and other resources that best suits a particular simulation model. We
present here a break-down of the main simulation paradigms, and discuss differing toolkits and
approaches that different researchers have taken to tackle coupled simulation and visualisation
in each paradigm
On Testing Quantum Programs
A quantum computer (QC) can solve many computational problems more
efficiently than a classic one. The field of QCs is growing: companies (such as
DWave, IBM, Google, and Microsoft) are building QC offerings. We position that
software engineers should look into defining a set of software engineering
practices that apply to QC's software. To start this process, we give examples
of challenges associated with testing such software and sketch potential
solutions to some of these challenges.Comment: A condensed version to appear in Proceedings of the 41st
International Conference on Software Engineering (ICSE 2019
COEL: A Web-based Chemistry Simulation Framework
The chemical reaction network (CRN) is a widely used formalism to describe
macroscopic behavior of chemical systems. Available tools for CRN modelling and
simulation require local access, installation, and often involve local file
storage, which is susceptible to loss, lacks searchable structure, and does not
support concurrency. Furthermore, simulations are often single-threaded, and
user interfaces are non-trivial to use. Therefore there are significant hurdles
to conducting efficient and collaborative chemical research. In this paper, we
introduce a new enterprise chemistry simulation framework, COEL, which
addresses these issues. COEL is the first web-based framework of its kind. A
visually pleasing and intuitive user interface, simulations that run on a large
computational grid, reliable database storage, and transactional services make
COEL ideal for collaborative research and education. COEL's most prominent
features include ODE-based simulations of chemical reaction networks and
multicompartment reaction networks, with rich options for user interactions
with those networks. COEL provides DNA-strand displacement transformations and
visualization (and is to our knowledge the first CRN framework to do so), GA
optimization of rate constants, expression validation, an application-wide
plotting engine, and SBML/Octave/Matlab export. We also present an overview of
the underlying software and technologies employed and describe the main
architectural decisions driving our development. COEL is available at
http://coel-sim.org for selected research teams only. We plan to provide a part
of COEL's functionality to the general public in the near future.Comment: 23 pages, 12 figures, 1 tabl
The Optimal Gravitational Lens Telescope
Given an observed gravitational lens mirage produced by a foreground
deflector (cf. galaxy, quasar, cluster,...), it is possible via numerical lens
inversion to retrieve the real source image, taking full advantage of the
magnifying power of the cosmic lens. This has been achieved in the past for
several remarkable gravitational lens systems. Instead, we propose here to
invert an observed multiply imaged source directly at the telescope using an
ad-hoc optical instrument which is described in the present paper. Compared to
the previous method, this should allow one to detect fainter source features as
well as to use such an optimal gravitational lens telescope to explore even
fainter objects located behind and near the lens. Laboratory and numerical
experiments illustrate this new approach
- …