330 research outputs found
A genetic-algorithms based evolutionary computational neural network for modelling spatial interaction data
Building a feedforward computational neural network model (CNN) involves two distinct tasks: determination of the network topology and weight estimation. The specification of a problem adequate network topology is a key issue and the primary focus of this contribution. Up to now, this issue has been either completely neglected in spatial application domains, or tackled by search heuristics (see Fischer and Gopal 1994). With the view of modelling interactions over geographic space, this paper considers this problem as a global optimization problem and proposes a novel approach that embeds backpropagation learning into the evolutionary paradigm of genetic algorithms. This is accomplished by interweaving a genetic search for finding an optimal CNN topology with gradient-based backpropagation learning for determining the network parameters. Thus, the model builder will be relieved of the burden of identifying appropriate CNN-topologies that will allow a problem to be solved with simple, but powerful learning mechanisms, such as backpropagation of gradient descent errors. The approach has been applied to the family of three inputs, single hidden layer, single output feedforward CNN models using interregional telecommunication traffic data for Austria, to illustrate its performance and to evaluate its robustness.
Soft computing for tool life prediction a manufacturing application of neural - fuzzy systems
Tooling technology is recognised as an element of vital importance within the manufacturing industry. Critical tooling decisions related to tool selection, tool life management, optimal determination of cutting conditions and on-line machining process monitoring and control are based on the existence of reliable detailed process models. Among the decisive factors of process planning and control activities, tool wear and tool life considerations hold a dominant role. Yet, both off-line tool life prediction, as well as real tune tool wear identification and prediction are still issues open to research. The main reason lies with the large number of factors, influencing tool wear, some of them being of stochastic nature. The inherent variability of workpiece materials, cutting tools and machine characteristics, further increases the uncertainty about the machining optimisation problem. In machining practice, tool life prediction is based on the availability of data provided from tool manufacturers, machining data handbooks or from the shop floor. This thesis recognises the need for a data-driven, flexible and yet simple approach in predicting tool life. Model building from sample data depends on the availability of a sufficiently rich cutting data set. Flexibility requires a tool-life model with high adaptation capacity. Simplicity calls for a solution with low complexity and easily interpretable by the user. A neural-fuzzy systems approach is adopted, which meets these targets and predicts tool life for a wide range of turning operations. A literature review has been carried out, covering areas such as tool wear and tool life, neural networks, frizzy sets theory and neural-fuzzy systems integration. Various sources of tool life data have been examined. It is concluded that a combined use of simulated data from existing tool life models and real life data is the best policy to follow. The neurofuzzy tool life model developed is constructed by employing neural network-like learning algorithms. The trained model stores the learned knowledge in the form of frizzy IF-THEN rules on its structure, thus featuring desired transparency. Low model complexity is ensured by employing an algorithm which constructs a rule base of reduced size from the available data. In addition, the flexibility of the developed model is demonstrated by the ease, speed and efficiency of its adaptation on the basis of new tool life data. The development of the neurofuzzy tool life model is based on the Fuzzy Logic Toolbox (vl.0) of MATLAB (v4.2cl), a dedicated tool which facilitates design and evaluation of fuzzy logic systems. Extensive results are presented, which demonstrate the neurofuzzy model predictive performance. The model can be directly employed within a process planning system, facilitating the optimisation of turning operations. Recommendations aremade for further enhancements towards this direction
Incremental and stable training algorithm for wind turbine neural modeling
Training and topology design of artificial neuralnetworks are important issues with largeapplication. This paper deals with an improvedalgorithm for feed forward neural networks (FNN)Â straining. The association of an incrementalapproach and the Lyapunov stability theoryaccomplishes both good generalization and stabletraining process. The algorithm is tested on windturbine modeling. Compared to the incrementalapproach and to the Lyapunov stability basedmethod, the association of both strategies givesinteresting results
Manifold Learning in Atomistic Simulations: A Conceptual Review
Analyzing large volumes of high-dimensional data requires dimensionality
reduction: finding meaningful low-dimensional structures hidden in their
high-dimensional observations. Such practice is needed in atomistic simulations
of complex systems where even thousands of degrees of freedom are sampled. An
abundance of such data makes gaining insight into a specific physical problem
strenuous. Our primary aim in this review is to focus on unsupervised machine
learning methods that can be used on simulation data to find a low-dimensional
manifold providing a collective and informative characterization of the studied
process. Such manifolds can be used for sampling long-timescale processes and
free-energy estimation. We describe methods that can work on datasets from
standard and enhanced sampling atomistic simulations. Unlike recent reviews on
manifold learning for atomistic simulations, we consider only methods that
construct low-dimensional manifolds based on Markov transition probabilities
between high-dimensional samples. We discuss these techniques from a conceptual
point of view, including their underlying theoretical frameworks and possible
limitations
Space-partitioning with cascade-connected ANN structures for positioning in mobile communication systems
The world around us is getting more connected with each day passing by – new portable
devices employing wireless connections to various networks wherever one might be. Locationaware
computing has become an important bit of telecommunication services and industry. For
this reason, the research efforts on new and improved localisation algorithms are constantly
being performed. Thus far, the satellite positioning systems have achieved highest popularity
and penetration regarding the global position estimation. In spite the numerous investigations
aimed at enabling these systems to equally procure the position in both indoor and outdoor
environments, this is still a task to be completed.
This research work presented herein aimed at improving the state-of-the-art positioning
techniques through the use of two highly popular mobile communication systems: WLAN and
public land mobile networks. These systems already have widely deployed network structures
(coverage) and a vast number of (inexpensive) mobile clients, so using them for additional,
positioning purposes is rational and logical.
First, the positioning in WLAN systems was analysed and elaborated. The indoor test-bed,
used for verifying the models’ performances, covered almost 10,000m2 area. It has been chosen
carefully so that the positioning could be thoroughly explored. The measurement campaigns
performed therein covered the whole of test-bed environment and gave insight into location
dependent parameters available in WLAN networks. Further analysis of the data lead to
developing of positioning models based on ANNs.
The best single ANN model obtained 9.26m average distance error and 7.75m median distance
error. The novel positioning model structure, consisting of cascade-connected ANNs, improved
those results to 8.14m and 4.57m, respectively. To adequately compare the proposed
techniques with other, well-known research techniques, the environment positioning error
parameter was introduced. This parameter enables to take the size of the test environment into
account when comparing the accuracy of the indoor positioning techniques.
Concerning the PLMN positioning, in-depth analysis of available system parameters and
signalling protocols produced a positioning algorithm, capable of fusing the system received
signal strength parameters received from multiple systems and multiple operators. Knowing
that most of the areas are covered by signals from more than one network operator and even
more than one system from one operator, it becomes easy to note the great practical value of
this novel algorithm. On the other hand, an extensive drive-test measurement campaign,
covering more than 600km in the central areas of Belgrade, was performed. Using this algorithm and applying the single ANN models to the recorded measurements, a 59m average
distance error and 50m median distance error were obtained. Moreover, the positioning in
indoor environment was verified and the degradation of performances, due to the crossenvironment
model use, was reported: 105m average distance error and 101m median distance
error.
When applying the new, cascade-connected ANN structure model, distance errors were
reduced to 26m and 2m, for the average and median distance errors, respectively.
The obtained positioning accuracy was shown to be good enough for the implementation of a
broad scope of location based services by using the existing and deployed, commonly
available, infrastructure
An instruction systolic array architecture for multiple neural network types
Modern electronic systems, especially sensor and imaging systems, are beginning to
incorporate their own neural network subsystems. In order for these neural systems to learn in
real-time they must be implemented using VLSI technology, with as much of the learning
processes incorporated on-chip as is possible. The majority of current VLSI implementations
literally implement a series of neural processing cells, which can be connected together in an
arbitrary fashion. Many do not perform the entire neural learning process on-chip, instead
relying on other external systems to carry out part of the computation requirements of the
algorithm.
The work presented here utilises two dimensional instruction systolic arrays in an attempt to
define a general neural architecture which is closer to the biological basis of neural networks - it
is the synapses themselves, rather than the neurons, that have dedicated processing units. A
unified architecture is described which can be programmed at the microcode level in order to
facilitate the processing of multiple neural network types.
An essential part of neural network processing is the neuron activation function, which can
range from a sequential algorithm to a discrete mathematical expression. The architecture
presented can easily carry out the sequential functions, and introduces a fast method of
mathematical approximation for the more complex functions. This can be evaluated on-chip,
thus implementing the entire neural process within a single system.
VHDL circuit descriptions for the chip have been generated, and the systolic processing
algorithms and associated microcode instruction set for three different neural paradigms have
been designed. A software simulator of the architecture has been written, giving results for
several common applications in the field
Battery States Monitoring and its Application in Energy Optimization of Hybrid Electric Vehicles
L'abstract è presente nell'allegato / the abstract is in the attachmen
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