A. Gonzalez

High voltage multilevel converter with regeneration capability

This paper presents a multilevel converter with regeneration capability. The converter is based on the series connection of several power cells, each working with reduced voltage and with an active front end at the line side. This paper presents the control method of each cell, the use of phase-shifting techniques to reduce the current distortion and criteria to select the connection of the cells. The converter generates practically sinusoidal currents at the load and at the input and works with very high power factor.

IRI-h, a Java-based distance education system: architecture and performance

We used our Original Interactive Remote Instruction (IRI) system to teach scores of university classes over the past years at sites up to 300 km apart. While this system is a prototype, its use in real classes allows us to deal with crucial issues in distributed education instruction systems. We describe our motivation and vision for a reimplementation of IRI that supports synchronous and asynchronous distance education. This new version, called IRI-h (h for hetergeneous), is coded in Java and executes on several different platforms. IRI-h extends IRI both to multiple platforms and heterogeneous network experiences with the developing prototype, including preliminary performance evaluation, and also unresolved issues still to be addressed.

Light-weight stream synchronization framework for multimedia collaborative applications

Todays Internet best-effort services introduce unavoidable uncertainties in the data transfer delay and create the need for synchronization mechanisms that preserve the temporal relationship among streams of distributed multimedia applications. We present algorithms for stream synchronization that are immune to moderate clock skew between sender and receivers and take into account the different time constraints of each media. In our time model, we introduce the idea of a virtual observer, which perceives the session as being in the same room with a sender. We propose policies for delay management and special consideration is given to the time the algorithms take to reach steady state. We avoid the need for globally synchronized clocks for media synchronization by introducing the concept of users multimedia presence, which defines a new manner for combining streams coming from multiple sites. Finally, we evaluate this framework with traces collected from the Internet.

Use of Web technology for interactive remote instruction

Advancements in web technology are changing learning paradigms. In this paper we relate various learning paradigms to existing technology and describe two approaches in IRI to use web technology for synchronous sessions: web steering and control and automatic content synthesis using the web. IRI (for Interactive Remote Instruction) is a computer-based system to support distance education developed at Old Dominion University; it is being used to teach courses between sites up to 200 miles apart.

Real-time estimation of aerodynamic features for ambulatory voice biofeedback

The development of ambulatory voice monitoring devices has the potential to improve the diagnosis and treatment of voice disorders. In this proof-of-concept study, real-time biofeedback is incorporated into a smartphone-based platform that records and processes neck surface acceleration. The focus is on utilizing aerodynamic measures of vocal function as a basis for biofeedback. This is done using regressed Z-scores to compare recorded values to normative estimates based on sound pressure level and fundamental frequency. Initial results from the analysis of different voice qualities suggest that accelerometer-based estimates of aerodynamic parameters can be used for real-time ambulatory biofeedback.

Biomedical signal acquisition, processing and transmission using smartphone

This article describes technical aspects involved in the programming of a system of acquisition, processing and transmission of biomedical signals by using mobile devices. This task is aligned with the permanent development of new technologies for the diagnosis and sickness treatment, based on the feasibility of measuring continuously different variables as electrocardiographic signals, blood pressure, oxygen concentration, pulse or simply temperature. The contribution of this technology is settled on its portability and low cost, which allows its massive use. Specifically this work analyzes the feasibility of acquisition and the processing of signals from a standard smartphone. Work results allow to state that nowadays these equipments have enough processing capacity to execute signals acquisition systems. These systems along with external servers make it possible to imagine a near future where the possibility of making continuous measures of biomedical variables will not be restricted only to hospitals but will also begin to be more frequently used in the daily life and at home.

Lightweight scalable tool sharing for the Internet

Increased desktop processing power and network bandwidth have made feasible distributed multimedia collaborative systems. Such systems are characterized by video, audio and data exchanges. While there has been much research and development of protocols and services for video and audio transmission, less work has been focused on data sharing particularly when the data is being generated by an application in real time and in turns controlled by one or more of the participants in the collaborative session. This paper describes a protocol and its implementation for sharing desktop applications in a distributed collaborative session. Key objectives of this protocol are scalability and resilience to dropped packages and to participants joining and leaving a session. We describe design decisions and give results demonstrating the effect of two different compression algorithms and protocol parameters. Finally, Odust a tool sharing system built on the implementation of shared application views is described.

A regenerative cell with reduced input current harmonics for multilevel inverters

This work presents a basic unit for a medium voltage multilevel inverter, capable of regeneration of power from the load to the three-phase source. This basic cell uses a single-phase PWM rectifier to reduce the input current harmonics. The work is focused on the control, modeling and simulation of the regenerative cell, which generates practically sinusoidal currents at the output and at the input and works with near unity power factor. Experimental results obtained in the series parallel connection of two regenerative cells confirm the simulation studies.

Evaluation and improvement of multicast service in 802.11b

Wireless Technologies have allowed a fast growing of the Internet service in both public and private environments where wireless networks mostly consist of nodes interconnected with a fixed infrastructure; nevertheless, they do not offer a good performance in all the wide variety of services that are required for applications. Although the IEEE 802.11 MAC protocol is the standard for wireless LANs, this protocol shows a very poor performance and reliability compared with the multicast traffic transmitted in wired networks, this represents a significant challenge for existing 802.11 networks because it requires transmission over multiple unreliable channels to heterogeneous receivers with different connection bit rates and very limited feedback information to the sender. In this paper, we discuss the drawbacks of several protocols proposed in the literature that offer reliable multicast service. In addition, this work evaluates the performance of the wireless networks under multicast traffic and presents a proposal for actual IEEE802.11 networks to improve their efficiency. It uses a reliability control based on a polling service along with controlled retransmissions; this allows servicing nodes applications with a high efficiency without deteriorating fairness in the service. We present details of a prototype implementation and results that suggest that our protocol performs better than other proposed in terms of reliability as well as data throughput in our measurement scenarios.3