6,323 research outputs found
Security Policies as Membranes in Systems for Global Computing
We propose a simple global computing framework, whose main concern is code migration. Systems are structured in sites, and each site is divided into two parts: a computing body, and a membrane which regulates the interactions between the computing body and the external environment. More precisely, membranes are filters which control access to the associated site, and they also rely on the well-established notion of trust between sites. We develop a basic theory to express and enforce security policies via membranes. Initially, these only control the actions incoming agents intend to perform locally. We then adapt the basic theory to encompass more sophisticated policies, where the number of actions an agent wants to perform, and also their order, are considered
On the lexicographic representation of numbers
It is proven that, contrarily to the common belief, the notion of zero is not
necessary for having positional representations of numbers. Namely, for any
positive integer , a positional representation with the symbols for is given that retains all the essential properties of the usual
positional representation of base (over symbols for ).
Moreover, in this zero-free representation, a sequence of symbols identifies
the number that corresponds to the order number that the sequence has in the
ordering where shorter sequences precede the longer ones, and among sequences
of the same length the usual lexicographic ordering of dictionaries is
considered. The main properties of this lexicographic representation are proven
and conversion algorithms between lexicographic and classical positional
representations are given. Zero-free positional representations are relevantt
in the perspective of the history of mathematics, as well as, in the
perspective of emergent computation models, and of unconventional
representations of genomes.Comment: 15 page
Ultrafunctions and Applications
This paper deals with a new kind of generalized functions, called
"ultrafunctions" which have been introduced recently and developed in some
previous works. Their peculiarity is that they are based on a Non-Archimedean
field namely on a field which contains infinite and infinitesimal numbers.
Ultrafunctions have been introduced to provide generalized solutions to
equations which do not have any solutions not even among the distributions.
Some of these applications will be presented in the second part of this paper
Explicit Simplicial Discretization of Distributed-Parameter Port-Hamiltonian Systems
Simplicial Dirac structures as finite analogues of the canonical Stokes-Dirac
structure, capturing the topological laws of the system, are defined on
simplicial manifolds in terms of primal and dual cochains related by the
coboundary operators. These finite-dimensional Dirac structures offer a
framework for the formulation of standard input-output finite-dimensional
port-Hamiltonian systems that emulate the behavior of distributed-parameter
port-Hamiltonian systems. This paper elaborates on the matrix representations
of simplicial Dirac structures and the resulting port-Hamiltonian systems on
simplicial manifolds. Employing these representations, we consider the
existence of structural invariants and demonstrate how they pertain to the
energy shaping of port-Hamiltonian systems on simplicial manifolds
On the dynamics of random neuronal networks
We study the mean-field limit and stationary distributions of a pulse-coupled
network modeling the dynamics of a large neuronal assemblies. Our model takes
into account explicitly the intrinsic randomness of firing times, contrasting
with the classical integrate-and-fire model. The ergodicity properties of the
Markov process associated to finite networks are investigated. We derive the
limit in distribution of the sample path of the state of a neuron of the
network when its size gets large. The invariant distributions of this limiting
stochastic process are analyzed as well as their stability properties. We show
that the system undergoes transitions as a function of the averaged
connectivity parameter, and can support trivial states (where the network
activity dies out, which is also the unique stationary state of finite networks
in some cases) and self-sustained activity when connectivity level is
sufficiently large, both being possibly stable.Comment: 37 pages, 3 figure
Efficient Dynamic Access Analysis Using JavaScript Proxies
JSConTest introduced the notions of effect monitoring and dynamic effect
inference for JavaScript. It enables the description of effects with path
specifications resembling regular expressions. It is implemented by an offline
source code transformation.
To overcome the limitations of the JSConTest implementation, we redesigned
and reimplemented effect monitoring by taking advantange of JavaScript proxies.
Our new design avoids all drawbacks of the prior implementation. It guarantees
full interposition; it is not restricted to a subset of JavaScript; it is
self-maintaining; and its scalability to large programs is significantly better
than with JSConTest.
The improved scalability has two sources. First, the reimplementation is
significantly faster than the original, transformation-based implementation.
Second, the reimplementation relies on the fly-weight pattern and on trace
reduction to conserve memory. Only the combination of these techniques enables
monitoring and inference for large programs.Comment: Technical Repor
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