59,238 research outputs found
Recommended from our members
An interactive multimedia learning environment for VLSI built with COSMOS
This paper presents Bigger Bits, an interactive multimedia learning environment that teaches students about VLSI within the context of computer electronics. The system was built with COSMOS (Content Oriented semantic Modelling Overlay Scheme), which is a modelling scheme that we developed for enabling the semantic content of multimedia to be used within interactive systems
Co-occurrence Vectors from Corpora vs. Distance Vectors from Dictionaries
A comparison was made of vectors derived by using ordinary co-occurrence
statistics from large text corpora and of vectors derived by measuring the
inter-word distances in dictionary definitions. The precision of word sense
disambiguation by using co-occurrence vectors from the 1987 Wall Street Journal
(20M total words) was higher than that by using distance vectors from the
Collins English Dictionary (60K head words + 1.6M definition words). However,
other experimental results suggest that distance vectors contain some different
semantic information from co-occurrence vectors.Comment: 6 pages, appeared in the Proc. of COLING94 (pp. 304-309)
Constraint Programming viewed as Rule-based Programming
We study here a natural situation when constraint programming can be entirely
reduced to rule-based programming. To this end we explain first how one can
compute on constraint satisfaction problems using rules represented by simple
first-order formulas. Then we consider constraint satisfaction problems that
are based on predefined, explicitly given constraints. To solve them we first
derive rules from these explicitly given constraints and limit the computation
process to a repeated application of these rules, combined with labeling.We
consider here two types of rules. The first type, that we call equality rules,
leads to a new notion of local consistency, called {\em rule consistency} that
turns out to be weaker than arc consistency for constraints of arbitrary arity
(called hyper-arc consistency in \cite{MS98b}). For Boolean constraints rule
consistency coincides with the closure under the well-known propagation rules
for Boolean constraints. The second type of rules, that we call membership
rules, yields a rule-based characterization of arc consistency. To show
feasibility of this rule-based approach to constraint programming we show how
both types of rules can be automatically generated, as {\tt CHR} rules of
\cite{fruhwirth-constraint-95}. This yields an implementation of this approach
to programming by means of constraint logic programming. We illustrate the
usefulness of this approach to constraint programming by discussing various
examples, including Boolean constraints, two typical examples of many valued
logics, constraints dealing with Waltz's language for describing polyhedral
scenes, and Allen's qualitative approach to temporal logic.Comment: 39 pages. To appear in Theory and Practice of Logic Programming
Journa
O2 signature in thin and thick O2-H2O ices
Aims. In this paper we investigate the detectability of the molecular oxygen
in icy dust grain mantles towards astronomical objects. Methods. We present a
systematic set of experiments with O2-H2O ice mixtures designed to disentangle
how the molecular ratio affects the O2 signature in the mid- and near-infrared
spectral regions. All the experiments were conducted in a closed-cycle helium
cryostat coupled to a Fourier transform infrared spectrometer. The ice mixtures
comprise varying thicknesses from 8 10 to 3 m. The
absorption spectra of the O2-H2O mixtures are also compared to the one of pure
water. In addition, the possibility to detect the O2 in icy bodies and in the
interstellar medium is discussed. Results. We are able to see the O2 feature at
1551 cm even for the most diluted mixture of H2O : O2 = 9 : 1,
comparable to a ratio of O2/H2O = 10 % which has already been detected in situ
in the coma of the comet 67P/Churyumov-Gerasimenko. We provide an estimate for
the detection of O2 with the future mission of the James Webb Space Telescope
(JWST).Comment: 11 pages, 10 figures, article in press, to appear in A&A 201
Geostationary secular dynamics revisited: application to high area-to-mass ratio objects
The long-term dynamics of the geostationary Earth orbits (GEO) is revisited
through the application of canonical perturbation theory. We consider a
Hamiltonian model accounting for all major perturbations: geopotential at order
and degree two, lunisolar perturbations with a realistic model for the Sun and
Moon orbits, and solar radiation pressure. The long-term dynamics of the GEO
region has been studied both numerically and analytically, in view of the
relevance of such studies to the issue of space debris or to the disposal of
GEO satellites. Past studies focused on the orbital evolution of objects around
a nominal solution, hereafter called the forced equilibrium solution, which
shows a particularly strong dependence on the area-to-mass ratio. Here, we i)
give theoretical estimates for the long-term behavior of such orbits, and ii)
we examine the nature of the forced equilibrium itself. In the lowest
approximation, the forced equilibrium implies motion with a constant non-zero
average `forced eccentricity', as well as a constant non-zero average
inclination, otherwise known in satellite dynamics as the inclination of the
invariant `Laplace plane'. Using a higher order normal form, we demonstrate
that this equilibrium actually represents not a point in phase space, but a
trajectory taking place on a lower-dimensional torus. We give analytical
expressions for this special trajectory, and we compare our results to those
found by numerical orbit propagation. We finally discuss the use of proper
elements, i.e., approximate integrals of motion for the GEO orbits.Comment: Accepted for publication in CMD
Proceedings of the Conference on Human and Economic Resources
This paper investigates the relative efficiency of public (state) libraries of major cities in Turkey by applying a data envelopment analysis. Scale, technical, and overall efficiency scores are calculated. It is found that there is a negative correlation between economic and social development index of the cities and efficiency scores of state libraries of same cities. In order to understand the sources of technical inefficiencies, the slack analysis is employed. Book collection and library staff are turned out to be the most problematic inputs and library members and lending of the books the most problematic outputs.public libraries, efficiency, data envelopment analysis, Turkey
Residues and Topological Yang-Mills Theory in Two Dimensions
A residue formula which evaluates any correlation function of topological
Yang-Mills theory with arbitrary magnetic flux insertion in two
dimensions are obtained. Deformations of the system by two form operators are
investigated in some detail. The method of the diagonalization of a matrix
valued field turns out to be useful to compute various physical quantities. As
an application we find the operator that contracts a handle of a Riemann
surface and a genus recursion relation.Comment: 23 pages, some references added, to appear in Rev.Math.Phy
Recommended from our members
Mass spectrometric analysis of small negative ions (e/m < 100) produced by Trichel pulse negative corona discharge fed by ozonised air
Mass spectrometric analysis of small negative ions (e/m < 100) produced by DC negative corona discharge in ozonised wet air both in flow and flow-stopped regimes was conducted at pressure of 30 kPa. The point-to-plain electrode system has been used. The yield of individual ions is strongly affected by trace concentrations of ozone in both regimes. Ozone concentration greater than 25 ppm is sufficient to completely suppress the appearance of O2- and a NO2- ion as well as theirs clusters in the mass spectra. The temporal increase in concentration of NO3- ions and NO3-.(H2O)n (n = 1, 2) hydrated clusters was observed in flow-stopped regime accompanied by reduction in yield of CO3- ion and its water clusters CO3-.(H2O)n (n = 1, 2), which otherwise are the dominant ions in flowing wet air free of ozone. In contrast the addition of ozone into the flow of wet air resulted in evident increase in abundance of the clusters CO3-.(H2O)n (n = 1, 2). This is an evidence of an active role of nitrous oxide produced in flow-stopped regime in sufficient amount. The measured electrical conductivity of drift region confirmed the role of additional dissociative attachment of electrons by ozone molecules as well as a formation of clusters of lower mobility with increasing ozone concentration in the discharge gap
- …