4,727 research outputs found
Towards an Efficient Evaluation of General Queries
Database applications often require to
evaluate queries containing quantifiers or disjunctions,
e.g., for handling general integrity constraints. Existing
efficient methods for processing quantifiers depart from the
relational model as they rely on non-algebraic procedures.
Looking at quantified query evaluation from a new angle,
we propose an approach to process quantifiers that makes
use of relational algebra operators only. Our approach
performs in two phases. The first phase normalizes the
queries producing a canonical form. This form permits to
improve the translation into relational algebra performed
during the second phase. The improved translation relies
on a new operator - the complement-join - that generalizes
the set difference, on algebraic expressions of universal
quantifiers that avoid the expensive division operator in
many cases, and on a special processing of disjunctions by
means of constrained outer-joins. Our method achieves an
efficiency at least comparable with that of previous
proposals, better in most cases. Furthermore, it is considerably
simpler to implement as it completely relies on
relational data structures and operators
Modeling phase transition and metastable phases
We propose a model that describes phase transition including metastable
phases present in the van der Waals Equation of State (EoS). We introduce a
dynamical system that is able to depict the mass transfer between two phases,
for which equilibrium states are both metastable and stable states, including
mixtures. The dynamical system is then used as a relaxation source term in a
isothermal two-phase model. We use a Finite volume scheme (FV) that treats the
convective part and the source term in a fractional step way. Numerical results
illustrate the ability of the model to capture phase transition and metastable
states
Sonar and radar SAR processing for parking lot detection
In this paper, SAR processing algorithms for automotive applications are presented and illustrated on data from non-trivial test scenes. The chosen application is parking lot detection. Laboratory results obtained with a teaching sonar experiment emphasize the resolution improvement introduced with range-Doppler SAR processing. A similar improvement is then confirmed through full scale measurements performed with an automotive radar prototype operating at 77GHz in very close range conditions, typical
of parking lot detection. The collected data allows a performance comparison between different SAR processing algorithms for realistic targets
Global solvability of a networked integrate-and-fire model of McKean-Vlasov type
We here investigate the well-posedness of a networked integrate-and-fire
model describing an infinite population of neurons which interact with one
another through their common statistical distribution. The interaction is of
the self-excitatory type as, at any time, the potential of a neuron increases
when some of the others fire: precisely, the kick it receives is proportional
to the instantaneous proportion of firing neurons at the same time. From a
mathematical point of view, the coefficient of proportionality, denoted by
, is of great importance as the resulting system is known to blow-up
for large values of . In the current paper, we focus on the
complementary regime and prove that existence and uniqueness hold for all time
when is small enough.Comment: Published at http://dx.doi.org/10.1214/14-AAP1044 in the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Web and Semantic Web Query Languages
A number of techniques have been developed to facilitate
powerful data retrieval on the Web and Semantic Web. Three categories
of Web query languages can be distinguished, according to the format
of the data they can retrieve: XML, RDF and Topic Maps. This article
introduces the spectrum of languages falling into these categories
and summarises their salient aspects. The languages are introduced using
common sample data and query types. Key aspects of the query
languages considered are stressed in a conclusion
Reactivity on the Web
Reactivity, the ability to detect simple and composite events and respond in a timely
manner, is an essential requirement in many present-day information systems. With
the emergence of new, dynamic Web applications, reactivity on the Web is receiving
increasing attention. Reactive Web-based systems need to detect and react not only
to simple events but also to complex, real-life situations. This paper introduces
XChange, a language for programming reactive behaviour on the Web, emphasising
the querying of event data and detection of composite events
Doeblin Trees
This paper is centered on the random graph generated by a Doeblin-type
coupling of discrete time processes on a countable state space whereby when two
paths meet, they merge. This random graph is studied through a novel subgraph,
called a bridge graph, generated by paths started in a fixed state at any time.
The bridge graph is made into a unimodular network by marking it and selecting
a root in a specified fashion. The unimodularity of this network is leveraged
to discern global properties of the larger Doeblin graph. Bi-recurrence, i.e.,
recurrence both forwards and backwards in time, is introduced and shown to be a
key property in uniquely distinguishing paths in the Doeblin graph, and also a
decisive property for Markov chains indexed by . Properties related
to simulating the bridge graph are also studied.Comment: 44 pages, 4 figure
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