128,833 research outputs found
Logical Specification and Analysis of Fault Tolerant Systems through Partial Model Checking
This paper presents a framework for a logical characterisation of fault tolerance and its formal analysis based on partial model checking techniques. The framework requires a fault tolerant system to be modelled using a formal calculus, here the CCS process algebra. To this aim we propose a uniform modelling scheme in which to specify a formal model of the system, its failing behaviour and possibly its fault-recovering procedures. Once a formal model is provided into our scheme, fault tolerance - with respect to a given property - can be formalized as an equational Āµ-calculus formula. This formula expresses in a logic formalism, all the fault scenarios satisfying that fault tolerance property. Such a characterisation understands the analysis of fault tolerance as a form of analysis of open systems and thank to partial model checking strategies, it can be made independent on any particular fault assumption. Moreover this logical characterisation makes possible the fault-tolerance verification problem be expressed as a general Āµ-calculus validation problem, for solving which many theorem proof techniques and tools are available. We present several analysis methods showing the flexibility of our approach
Vibrational properties of alpha- and sigma-phase Fe-Cr alloy
Experimental investigation as well as theoretical calculations, of the
Fe-partial phonon density-of-states (DOS) for nominally Fe_52.5Cr_47.5 alloy
having (a) alpha- and (b) sigma-phase structure were carried out. The former at
sector 3-ID of the Advanced Photon Source, using the method of nuclear resonant
inelastic X-ray scattering, and the latter with the direct method [K. Parlinski
et al., Phys. Rev. Lett. {78, 4063 (1997)]. The characteristic features of
phonon DOS, which differentiate one phase from the other, were revealed and
successfully reproduced by the theory. Various data pertinent to the dynamics
such as Lamb-Mossbauer factor, f, kinetic energy per atom, E_k, and the mean
force constant, D, were directly derived from the experiment and the
theoretical calculations, while vibrational specific heat at constant volume,
C_V, and vibrational entropy, S were calculated using the Fe-partial DOS. Using
the values of f and C_V, we determined values for Debye temperatures, T_D. An
excellent agreement for some quantities derived from experiment and
first-principles theory, like C_V and quite good one for others like D and S
was obtained.Comment: 4 pages, 3 figure
Formalization, Mechanization and Automation of G\"odel's Proof of God's Existence
G\"odel's ontological proof has been analysed for the first-time with an
unprecedent degree of detail and formality with the help of higher-order
theorem provers. The following has been done (and in this order): A detailed
natural deduction proof. A formalization of the axioms, definitions and
theorems in the TPTP THF syntax. Automatic verification of the consistency of
the axioms and definitions with Nitpick. Automatic demonstration of the
theorems with the provers LEO-II and Satallax. A step-by-step formalization
using the Coq proof assistant. A formalization using the Isabelle proof
assistant, where the theorems (and some additional lemmata) have been automated
with Sledgehammer and Metis.Comment: 2 page
Differences in intention to use educational RSS feeds between Lebanese and British students: A multiāgroup analysis based on the technology acceptance model
Really Simple Syndication (RSS) offers a means for university students to receive timely updates from virtual learning environments. However, despite its utility, only 21% of home students surveyed at a university in Lebanon claim to have ever used the technology. To investigate whether national culture could be an influence on intention to use RSS, the survey was extended to British students in the UK. Using the Technology Adoption Model (TAM) as a research framework, 437 students responded to a questionnaire containing four constructs: behavioral intention to use; attitude towards benefit; perceived usefulness; and perceived ease of use. Principle components analysis and structural equation modelling were used to explore the psychometric qualities and utility of TAM in both contexts. The results show that adoption was significantly higher, but also modest, in the British context at 36%. Configural and metric invariance were fully supported, while scalar and factorial invariance were partially supported. Further analysis shows significant differences between perceived usefulness and perceived ease of use across the two contexts studied. Therefore, it is recommended that faculty demonstrate to students how educational RSS feeds can be used effectively to increase awareness and emphasize usefulness in both contexts
Parallel Chip Firing Game associated with n-cube orientations
We study the cycles generated by the chip firing game associated with n-cube
orientations. We show the existence of the cycles generated by parallel
evolutions of even lengths from 2 to on (n >= 1), and of odd
lengths different from 3 and ranging from 1 to on (n >= 4)
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