Francisco J. Torres-Rojas

Performance Evaluation of Plausible Clocks

Plausible Clocks do not characterize causality [6] but, under appropriate circumstances, their accuracy is close to vector clocks. This paper explores the effects that several factors have on the performance of these clocks.

Analyzing convergence in consistency models for distributed objects

At instant t, two or more sites could perceive different values for the same distributed object X. However, depending on the consistency protocol used, it might be expected that, after a while, every site in the system should see the same value for this object. In this paper, we present a formalization of the concept of convergence and analyze its relationships with several consistency models. Among other things, we claim that, by itself, sequential consistency is not a convergent protocol.

Object Recognition Using Hierarchical Temporal Memory

At this time, great effort is being directed toward developing problem-solving technology that mimic human cognitive processes. Research has been done to develop object recognition using Computer Vision for daily tasks such as secure access, traffic management, and robotic behavior. For this research, four different machine learning algorithms have been developed to overcome the computer vision problem of object recognition. Hierarchical temporal memory (HTM) is an emerging technology based on biological methods of the human cortex to learn patterns. This research applied an HTM algorithm to images (video sequences) in order to compare this technique against two others: support vector machines (SVM) and artificial neural networks (ANN). It was concluded that HTM was the most effective.

Convergence Through a Weak Consistency Model

Given a distributed system with several shared objects and many processes concurrently updating and reading them, it is convenient that the system achieves convergence on the value of these objects. Such property can be guaranteed depending on the consistency model being employed. Causal Consistency is a weak consistency model that is easy and cheap to implement. However, due to the lack of real-time considerations, this model cannot oer convergence. A solution for overcoming that problem is to include time aspects within the framework of the model. This is the aim of Timed Causal Consistency.

Sensibility analysis of the Trace Transform on land coverage images

Aerial or satellital images may be used to produce terrain coverage maps, which in time are a very useful and important tool for decision-making in several fields including biodiversity, telecommunications and natural disaster management. The Trace Transform method can be used to process these images. This method extracts features from the images by applying a series of functionals to produce a numeric representation that will be used for classification later on. This model depends on several factors in order to have an efficient operation, among them, the frequency parameters of the traces, classifier type and land coverage. Experimentation on feature extraction time and precision rate revealed that the frequency parameters, specially Δτ, and the classifier type can affect both of them.

Distributed detection of debris flows on a wireless sensor network

Debris flows are very destructive phenomena that cause damage to population living near rivers. Current warning systems for these phenomena are based on fixed instrumentation located at certain points through the river or indirectly, through remote measurements; as a result, the information they provide is limited, as it lacks real-time and precise data about the event location and its speed. In this paper, we introduce a set of algorithms and protocols for debris flows detection in rivers, using a wireless sensor network. The proposed detection protocol is distributed and decentralized, as it does not rely on a central coordinator to decide on the presence of the event. The proposed algorithms and protocols were evaluated on a simulator, in order to evaluate its performance. Results show that the algorithms are capable of detecting the phenomenon and alert people in the danger area with enough anticipation to prevent a tragedy.

Real-time based strong consistency for distributed objects

A distributed computation satisfies sequential consistency if it is possible to establish a legal ordering of all the operations such that the program order of each site in the distributed system is respected. However, sequential consistency does not necessarily consider the particular real-time instant at which each operation is executed. A timed consistency model addresses how quickly the effects of an operation are perceived by the rest of the system, by requiring that if a write operation is executed at time t, it must be visible to the entire distributed system by time t+/spl Delta/.Timed consistency generalizes several existing consistency criteria and it is well suited for applications where the action of one user must be seen by others in a timely fashion.