290,778 research outputs found
A new model for solution of complex distributed constrained problems
In this paper we describe an original computational model for solving
different types of Distributed Constraint Satisfaction Problems (DCSP). The
proposed model is called Controller-Agents for Constraints Solving (CACS). This
model is intended to be used which is an emerged field from the integration
between two paradigms of different nature: Multi-Agent Systems (MAS) and the
Constraint Satisfaction Problem paradigm (CSP) where all constraints are
treated in central manner as a black-box. This model allows grouping
constraints to form a subset that will be treated together as a local problem
inside the controller. Using this model allows also handling non-binary
constraints easily and directly so that no translating of constraints into
binary ones is needed. This paper presents the implementation outlines of a
prototype of DCSP solver, its usage methodology and overview of the CACS
application for timetabling problems
Neural Distributed Autoassociative Memories: A Survey
Introduction. Neural network models of autoassociative, distributed memory
allow storage and retrieval of many items (vectors) where the number of stored
items can exceed the vector dimension (the number of neurons in the network).
This opens the possibility of a sublinear time search (in the number of stored
items) for approximate nearest neighbors among vectors of high dimension. The
purpose of this paper is to review models of autoassociative, distributed
memory that can be naturally implemented by neural networks (mainly with local
learning rules and iterative dynamics based on information locally available to
neurons). Scope. The survey is focused mainly on the networks of Hopfield,
Willshaw and Potts, that have connections between pairs of neurons and operate
on sparse binary vectors. We discuss not only autoassociative memory, but also
the generalization properties of these networks. We also consider neural
networks with higher-order connections and networks with a bipartite graph
structure for non-binary data with linear constraints. Conclusions. In
conclusion we discuss the relations to similarity search, advantages and
drawbacks of these techniques, and topics for further research. An interesting
and still not completely resolved question is whether neural autoassociative
memories can search for approximate nearest neighbors faster than other index
structures for similarity search, in particular for the case of very high
dimensional vectors.Comment: 31 page
Thermodynamics and statistical mechanics of frozen systems in inherent states
We discuss a Statistical Mechanics approach in the manner of Edwards to the
``inherent states'' (defined as the stable configurations in the potential
energy landscape) of glassy systems and granular materials. We show that at
stationarity the inherent states are distributed according a generalized Gibbs
measure obtained assuming the validity of the principle of maximum entropy,
under suitable constraints. In particular we consider three lattice models (a
diluted Spin Glass, a monodisperse hard-sphere system under gravity and a
hard-sphere binary mixture under gravity) undergoing a schematic ``tap
dynamics'', showing via Monte Carlo calculations that the time average of
macroscopic quantities over the tap dynamics and over such a generalized
distribution coincide. We also discuss about the general validity of this
approach to non thermal systems.Comment: 10 pages, 16 figure
High performance constraint satisfaction problem solving: State-recomputation versus state-copying.
Constraint Satisfaction Problems (CSPs) in Artificial Intelligence have been an important focus of research and have been a useful model for various applications such as scheduling, image processing and machine vision. CSPs are mathematical problems that try to search values for variables according to constraints. There are many approaches for searching solutions of non-binary CSPs. Traditionally, most CSP methods rely on a single processor. With the increasing popularization of multiple processors, parallel search methods are becoming alternatives to speed up the search process. Parallel search is a subfield of artificial intelligence in which the constraint satisfaction problem is centralized whereas the search processes are distributed among the different processors. In this thesis we present a forward checking algorithm solving non-binary CSPs by distributing different branches to different processors via message passing interface and execute it on a high performance distributed system called SHARCNET. However, the problem is how to efficiently communicate the state of the search among processors. Two communication models, namely, state-recomputation and state-copying via message passing, are implemented and evaluated. This thesis investigates the behaviour of communication from one process to another. The experimental results demonstrate that the state-recomputation model with tighter constraints obtains a better performance than the state-copying model, but when constraints become looser, the state-copying model is a better choice.Dept. of Computer Science. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2004 .Y364. Source: Masters Abstracts International, Volume: 44-01, page: 0417. Thesis (M.Sc.)--University of Windsor (Canada), 2005
Bypassing the Kochen-Specker theorem: an explicit non-contextual statistical model for the qutrit
We present an explicit non-contextual model of hidden variables for the
qutrit. The model consists of an infinite set of possible hidden configurations
uniformly distributed over a sphere, each one having a well-defined probability
density to happen and a well-defined non-contextual binary outcome, either
or , for every properly formulated test. The model reproduces the
predictions of quantum mechanics and, thus, it bypasses the constraints imposed
by the Kochen-Specker theorem and its subsequent reformulations. The crux of
the model is the observation that all these theorems crucially rely on an
implicit assumption that is not actually required by fundamental physical
principles, namely, the existence of an absolute frame of reference with
respect to which the polarization properties of the qutrit as well as the
orientation of the tests performed on it can be defined. We notice, on the
other hand, that pairs of compatible tests defined in such an hypothetical
absolute frame of reference that can be obtained from each other through a
global rotation that leaves the state of the qutrit unchanged would by
physically undistinguishable and, hence, equivalent under a gauge symmetry
transformation. This spurious gauge degree of freedom must be properly fixed in
order to build the statistical model for the qutrit. In two previous papers we
have shown that the same implicit assumption is also required in order to prove
both Bell's theorem and the Greenberger-Horne-Zeilinger theorem
On the Design and Analysis of Secure Inference Networks
Parallel-topology inference networks consist of spatially-distributed sensing agents that collect and transmit observations to a central node called the fusion center (FC), so that a global inference is made regarding the phenomenon-of-interest (PoI). In this dissertation, we address two types of statistical inference, namely binary-hypothesis testing and scalar parameter estimation in parallel-topology inference networks. We address three different types of security threats in parallel-topology inference networks, namely Eavesdropping (Data-Confidentiality), Byzantine (Data-Integrity) or Jamming (Data-Availability) attacks. In an attempt to alleviate information leakage to the eavesdropper, we present optimal/near-optimal binary quantizers under two different frameworks, namely differential secrecy where the difference in performances between the FC and Eve is maximized, and constrained secrecy where FC’s performance is maximized in the presence of tolerable secrecy constraints. We also propose near-optimal transmit diversity mechanisms at the sensing agents in detection networks in the presence of tolerable secrecy constraints. In the context of distributed inference networks with M-ary quantized sensing data, we propose a novel Byzantine attack model and find optimal attack strategies that minimize KL Divergence at the FC in the presence of both ideal and non-ideal channels. Furthermore, we also propose a novel deviation-based reputation scheme to detect Byzantine nodes in a distributed inference network. Finally, we investigate optimal jamming attacks in detection networks where the jammer distributes its power across the sensing and the communication channels. We also model the interaction between the jammer and a centralized detection network as a complete information zero-sum game. We find closed-form expressions for pure-strategy Nash equilibria and show that both the players converge to these equilibria in a repeated game. Finally, we show that the jammer finds no incentive to employ pure-strategy equilibria, and causes greater impact on the network performance by employing mixed strategies
Analysis of a Waveguide-Fed Metasurface Antenna
The metasurface concept has emerged as an advantageous reconfigurable antenna
architecture for beam forming and wavefront shaping, with applications that
include satellite and terrestrial communications, radar, imaging, and wireless
power transfer. The metasurface antenna consists of an array of metamaterial
elements distributed over an electrically large structure, each subwavelength
in dimension and with subwavelength separation between elements. In the antenna
configuration we consider here, the metasurface is excited by the fields from
an attached waveguide. Each metamaterial element can be modeled as a
polarizable dipole that couples the waveguide mode to radiation modes. Distinct
from the phased array and electronically scanned antenna (ESA) architectures, a
dynamic metasurface antenna does not require active phase shifters and
amplifiers, but rather achieves reconfigurability by shifting the resonance
frequency of each individual metamaterial element. Here we derive the basic
properties of a one-dimensional waveguide-fed metasurface antenna in the
approximation that the metamaterial elements do not perturb the waveguide mode
and are non-interacting. We derive analytical approximations for the array
factors of the 1D antenna, including the effective polarizabilities needed for
amplitude-only, phase-only, and binary constraints. Using full-wave numerical
simulations, we confirm the analysis, modeling waveguides with slots or
complementary metamaterial elements patterned into one of the surfaces.Comment: Original manuscript as submitted to Physical Review Applied (2017).
14 pages, 14 figure
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