Felipe Núñez

Increasing Sync Rate of Pulse-Coupled Oscillators via Phase Response Function Design: Theory and Application to Wireless Networks

This brief addresses the synchronization rate of weakly connected pulse-coupled oscillators (PCOs). We prove that besides the coupling strength, the phase response function is also a determinant of the synchronization rate. Inspired by the result, we propose to increase the synchronization rate of PCOs by designing the phase response function. This has important significance in the PCO-based clock synchronization of wireless networks. By designing the phase response function, the synchronization rate is increased even under a fixed transmission power. Given that the energy consumption in synchronization is determined by the product of synchronization time and transmission power, the new strategy reduces energy consumption in the clock synchronization. QualNet experiments confirm the theoretical results.

An event-driven simulator for multi-line metro systems and its application to Santiago de Chile metropolitan rail network

Metros are the principal means of public transportation in many of the world’s cities, and continue to grow in the face of rising demand. Expanding metro infrastructure is costly, however, and at a certain point becomes unsustainable. When this occurs the only feasible solution is to improve the train’s management system by using either offline approaches, such as pre-programming schedules which use historic information, or online approaches which employ system status information obtained during operation. A new planning or control system, be it on or off line, requires prior testing that usually involves conducting simulations. This paper presents the design and implementation of an event-driven dynamic simulator for multi-line metro systems, and its practical application for studying different operating strategies. The simulator is based on object-oriented programming and is capable of interacting with Matlab programs written by the user to design and evaluate real-time control strategies. This article describes the model upon which the simulator is based, presents the user interface, and demonstrates how to use the simulator for operating strategies evaluation in the Santiago de Chile multi-line metropolitan rail network.

Screening trial of human papillomavirus for early detection of cervical cancer in Santiago, Chile

Cervical cancer mortality in Chile is four times higher than in developed countries. We compared the accuracy of human papillomavirus (HPV) DNA testing and conventional Papanicolaou (Pap) testing to detect prevalent precancerous and cancerous lesions in the routine clinical practice of the public health system. Women aged 25 years and older residing in the area covered by three primary care centers of Santiago, Chile, were invited to participate. Eligible women received both HPV DNA (Hybrid Capture 2) and Pap testing. Women positive by either test (Pap: ASCUS+, HC2: RLU/CO ≥1.0) underwent colposcopy and biopsy, as did a sample of double‐negative women with an abnormal cervix at visual inspection or with risk factors for cervical lesions. Crude and verification bias‐corrected sensitivities and specificities were estimated. In total, 8,265 women (98.8% of eligible) had complete screening results. Of these, 10.7% were HPV positive, 1.7% were Pap positive and 1.1% were positive by both tests. In all, 931 (11.3%) women were screen‐positive, of whom 94.3% attended colposcopy. Additionally, 295 control women were invited for colposcopy, of whom 78% attended. In all, 42 CIN2, 45 CIN3 and 9 cancers were identified. Verification bias‐corrected sensitivity for CIN2+ (95% confidence interval) was 92.7% (84.4–96.8) for HPV and 22.1% (16.4–29.2) for Pap; corresponding specificities were 92.0% (91.4–92.6) and 98.9% (98.7–99.0). In conclusion, in routine clinical practice in a developing country, HPV testing was four times more sensitive for CIN2+ than Pap testing, identifying three times more CIN2+ lesions; HPV testing was easily implemented in our established cervical cancer prevention program.

Fault detection and isolation in cooperative mobile robots using multilayer architecture and dynamic observers

Mobile robot systems are being used more often in tasks that protect human operators from dangerous environments, but these benefits can be easily lost if the robots spend much of their time being repaired. This implies that any increment in their reliability will also improve their benefits. One way to achieve this is by adding redundant elements to the robot, but this adds complexity and cost to the design. On the other hand, cooperative mobile robots formed by members with the same basic structure provide a natural redundancy of elements, which may be used for reliability improvement. This work presents an architecture that takes advantage of the analytical and sensor redundancy present in groups of cooperative mobile robots in order to increase the reliability of the whole system. First, the design of the architecture is portrayed and the faults to be detected are described. The different layers of the system are then explained and analyzed using several simulations to test their capabilities and limitations. Finally, the experimental results on a group of small mobile robots are shown, validating the results delivered by simulations. These results show that the proposed architecture is able to detect and isolate correctly most of the faults tested.

Synchronization of Pulse-Coupled Oscillators on (Strongly) Connected Graphs

The synchronization of pulse-coupled oscillators (PCOs) interacting on general (strongly) connected graphs is addressed. It is shown that the network synchronizes if the phases are contained in an arc of length less than π, for every (strongly) connected interaction topology. Moreover, global synchronization is feasible in the all-to-all, strongly rooted, and connected bidirectional cases. Examples, counter-examples, and numerical simulations are given to illustrate the analytical findings.

Global synchronization of pulse-coupled oscillators interacting on cycle graphs

The importance of pulse-coupled oscillators (PCOs) in biology and engineering has motivated research to understand basic properties of PCO networks. Despite the large body of work addressing PCOs, a global synchronization result for networks that are more general than all-to-all connected is still unavailable. In this paper we address global synchronization of PCO networks described by cycle graphs. It is shown for the bidirectional cycle case that as the number of oscillators in the cycle grows, the coupling strength must be increased in order to guarantee synchronization for arbitrary initial conditions. For the unidirectional cycle case, the strongest coupling cannot ensure global synchronization yet a refractory period in the phase response curve is sufficient to enable global synchronization. Analytical findings are confirmed by numerical simulations.

Expectativas de estudiantes de medicina de pregrado en relación al perfil de médico esperado

Background: During the last few years, multiple new medical schools have emerged in Chile, associated to the constant preoccupation to provide a good quality medical care. This created the need to evaluate medical training programs and to open a discussion about the attributes that a good physician should have. Aim: To evaluate the medical student’s perception of the ideal medical doctor profile. Material and methods: An analytical, descriptive and cross sectional study was designed. Eleven second year, 11 third year, nine fourth year, 13 fifth year, 6 sixth year and 8 seventh year students were studied. Data collection was gathered by focus groups. Codes and triangulation were used for data analysis. Results: As attitudes and moral-ethical values, students valued the absence of discrimination a listening attitude and empathy. Among job related issues, they valued responsibility and punctuality. Emotional and legal self-care were valued as self related attitudes. Among skills, competences and capacities, a value was given to communicational skills, team work and professional easiness. Knowledge about medical and non medical topics was appraised. The valued attributes among duties and activities were patient diagnosis, treatment and education, team leadership and continuous medical training. Conclusions: These findings should help to design new curricula for medical schools (Rev Med Chile 2006; 134: 947-54). (Key words: Attitude of health personnel; Education; Schools, medical; Students, medical)

Statistical Analysis of the Pulse-Coupled Synchronization Strategy for Wireless Sensor Networks

Pulse-coupled synchronization is attracting increased attention in the sensor network community. Yet its properties have not been fully investigated. Using statistical analysis, we prove analytically that by controlling the number of connections at each node, synchronization can be guaranteed for generally pulse-coupled oscillators even in the presence of a refractory period. The approach does not require the initial phases to reside in half an oscillation cycle, which improves existing results. We also find that a refractory period can be strategically included to reduce idle listening at nearly no sacrifice to the synchronization probability. Given that reduced idle listening leads to higher energy efficiency in the synchronization process, the strategically added refractory period makes the synchronization scheme appealing to cheap sensor nodes, for which energy is a precious system resource. We also analyzed the pulse-coupled synchronization in the presence of unreliable communication links and obtained similar results. QualNet experimental results are given to confirm the effectiveness of the theoretical predictions.

Bio-inspired synchronization of wireless sensor networks for acoustic event detection systems

Detection of events using a network of simple field sensors has gained interest due to its low cost and robustness. Sensor networks have been extensively analyzed recently in terms of stability, robustness, and efficiency. Time synchronization has proven to be critical in sensor fusion applications where time of arrival is a decision property, and thus an accurate common time reference is required. In this work, we analyze the dependence on time synchronization of an acoustic event detection system, and we present a bio-inspired synchronization algorithm for wireless sensor networks capable of providing the system with a common time reference to enable accurate detection.

Bio-inspired hybrid control of pulse-coupled oscillators and application to synchronization of a wireless network

Pulse-coupled oscillators (PCOs) are limit cycle oscillators coupled in an impulsive rather than smooth manner. Its importance in biology and engineering has motivated the community to understand basic properties and design principles of PCO networks. In this work we address synchronization of PCO networks subject to both a global cue and local interactions using a hybrid systems approach. We characterize solutions and give synchronization conditions using phase response curves as design element. To illustrate the results, we provide an evaluation in QualNet™, a widely used commercial network simulator.