41,480 research outputs found
Synthesizing Modular Invariants for Synchronous Code
In this paper, we explore different techniques to synthesize modular
invariants for synchronous code encoded as Horn clauses. Modular invariants are
a set of formulas that characterizes the validity of predicates. They are very
useful for different aspects of analysis, synthesis, testing and program
transformation. We describe two techniques to generate modular invariants for
code written in the synchronous dataflow language Lustre. The first technique
directly encodes the synchronous code in a modular fashion. While in the second
technique, we synthesize modular invariants starting from a monolithic
invariant. Both techniques, take advantage of analysis techniques based on
property-directed reachability. We also describe a technique to minimize the
synthesized invariants.Comment: In Proceedings HCVS 2014, arXiv:1412.082
Structures performance, benefit, cost-study
New technology concepts and structural analysis development needs which could lead to improved life cycle cost for future high-bypass turbofans were studied. The NASA-GE energy efficient engine technology is used as a base to assess the concept benefits. Recommended programs are identified for attaining these generic structural and other beneficial technologies
Verifying the Safety of a Flight-Critical System
This paper describes our work on demonstrating verification technologies on a
flight-critical system of realistic functionality, size, and complexity. Our
work targeted a commercial aircraft control system named Transport Class Model
(TCM), and involved several stages: formalizing and disambiguating requirements
in collaboration with do- main experts; processing models for their use by
formal verification tools; applying compositional techniques at the
architectural and component level to scale verification. Performed in the
context of a major NASA milestone, this study of formal verification in
practice is one of the most challenging that our group has performed, and it
took several person months to complete it. This paper describes the methodology
that we followed and the lessons that we learned.Comment: 17 pages, 5 figure
Scientific publications of the bioscience programs division. Volume 5 - Planetary quarantine
Bibliography and indexes on planetary quarantin
Towards Practical Graph-Based Verification for an Object-Oriented Concurrency Model
To harness the power of multi-core and distributed platforms, and to make the
development of concurrent software more accessible to software engineers,
different object-oriented concurrency models such as SCOOP have been proposed.
Despite the practical importance of analysing SCOOP programs, there are
currently no general verification approaches that operate directly on program
code without additional annotations. One reason for this is the multitude of
partially conflicting semantic formalisations for SCOOP (either in theory or
by-implementation). Here, we propose a simple graph transformation system (GTS)
based run-time semantics for SCOOP that grasps the most common features of all
known semantics of the language. This run-time model is implemented in the
state-of-the-art GTS tool GROOVE, which allows us to simulate, analyse, and
verify a subset of SCOOP programs with respect to deadlocks and other
behavioural properties. Besides proposing the first approach to verify SCOOP
programs by automatic translation to GTS, we also highlight our experiences of
applying GTS (and especially GROOVE) for specifying semantics in the form of a
run-time model, which should be transferable to GTS models for other concurrent
languages and libraries.Comment: In Proceedings GaM 2015, arXiv:1504.0244
Full-scale aircraft simulation with cryogenic tunnels and status of the National Transonic Facility
The effect of thermal and caloric imperfections in cryogenic nitrogen on boundary layers was determined to indicate that in order to simulate nonadiabatic laminar or turbulent boundary layers in a cryogenic nitrogen wind tunnel, the flight enthalpy ratio, rather than the temperature ratio, should be reproduced. The absence of significant real gas effects on both viscous and inviscid flows makes it unlikely that there will be large real gas effects on the cryogenic tunnel simulation of shock boundary layer interactions or other complex flow conditions encountered in flight. Condensation effects were studied to determine the minimum usable temperature and indicated that under most circumstances free stream Mach number rather than maximum local Mach number determines the onset of condensation effects
VLSI Architecture and Design
Integrated circuit technology is rapidly approaching a state where feature sizes of one micron or less are tractable. Chip sizes are increasing slowly. These two developments result in considerably increased complexity in chip design. The physical characteristics of integrated circuit technology are also changing. The cost of communication will be dominating making new architectures and algorithms both feasible and desirable. A large
number of processors on a single chip will be possible. The cost of communication will make
designs enforcing locality superior to other types of designs.
Scaling down feature sizes results in increase of the delay that wires introduce. The delay even of metal wires will become significant. Time tends to be a local property which will make the design of globally synchronous systems more difficult. Self-timed systems will eventually become a necessity.
With the chip complexity measured in terms of logic devices increasing by more than an order of magnitude over the next few years the importance of efficient design methodologies and tools become crucial. Hierarchical and structured design are ways of dealing with the complexity of chip design. Structered design focuses on the information
flow and enforces a high degree of regularity. Both hierarchical and structured design encourage the use of cell libraries. The geometry of the cells in such libraries should be parameterized so that for instance cells can adjust there size to neighboring cells and make the proper interconnection. Cells with this quality can be used as a basis for "Silicon Compilers"
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