Juan José Serrano

Bio: Juan José Serrano is an academic researcher from Polytechnic University of Valencia. The author has contributed to research in topics: Wireless sensor network & Fault tolerance. The author has an hindex of 15, co-authored 71 publications receiving 1014 citations.

Underwater Acoustic Wireless Sensor Networks: Advances and Future Trends in Physical, MAC and Routing Layers

Abstract: This survey aims to provide a comprehensive overview of the current research on underwater wireless sensor networks, focusing on the lower layers of the communication stack, and envisions future trends and challenges. It analyzes the current state-of-the-art on the physical, medium access control and routing layers. It summarizes their security threads and surveys the currently proposed studies. Current envisioned niches for further advances in underwater networks research range from efficient, low-power algorithms and modulations to intelligent, energy-aware routing and medium access control protocols.

Adding instruction cache effect to schedulability analysis of preemptive real-time systems

Abstract: Cache memories are commonly avoided in real time systems because of their unpredictable behavior. Recently, some research has been done to obtain tighter bounds on the worst case execution time (WCET) of cached programs. These techniques usually assume a non preemptive underlying system. However, some techniques can be applied to allow the use of caches in preemptive systems. The paper describes how to incorporate the effect of instruction cache to the Response Time schedulability Analysis (RTA). RTA is an efficient analysis for preemptive fixed priority schedulers. We also compare through simulations the results of such an approach to both cache partitioning (increase of the cache predictability by assigning private cache partitions to tasks) and CRMA (Cached RMA: cache effect is incorporated in the utilization based rate monotonic schedulability analysis). The results show that the cached version of RTA (CRTA) clearly outperforms CRMA, however the partitioning scheme may be better depending on the system configuration. The obtained results bound the applicability domain for each method for a variety of hardware and workload configurations. The results can be used as design guidelines.

A low cost and high efficient acoustic modem for underwater sensor networks

Abstract: Underwater wireless sensor Networks (UWSN) will provide a variety of attractive working fields such as aquaculture, offshore exploitation, biological monitoring as well as water and seafloor pollution, seismic activity and ocean currents. A practical implementation of these applications will require spreading an important number of nodes to facilitate underwater monitoring by means of data acquiring, so it becomes a challenge to develop simple and reliable modem architectures to reduce both the cost in components and the developing time, still being efficient and robust. Moreover power consumption must be also considered due to energy harvesting difficulties in an underwater environment. This work is focused in the design and implementation of a low cost and energy efficient underwater modem. The paper presents a new acoustic modem design based on an original signal-conditioning model optimally adapted to commercial echo sounder based piezoelectric transducers. It represents a very low-cost solution with a power consumption level similar to current terrestrial wireless sensor networks. The modulation and demodulation algorithms are essential to define the modem architecture. In this work, they have been adapted to a low power microcontroller processing capabilities. The proposed modem architecture includes an 8-bit microcontroller and few external analog components. A binary Coherent-FSK modulation has been chosen because it is more efficient in terms of bandwidth than a non-coherent FSK. Coherent FSK modulation algorithm is quite simple, and can be easily implemented in an 8-bit microcontroller with negligible execution time. Demodulation algorithm is more complex and needs a low-power solution. The paper investigates different alternatives, obtaining a new optimal solution including an additional specific processing unit to the microprocessor core. Compared with previous researches that used microcontrollers, the presented approach also improves energy efficiency without lowering bit rate and bandwidth efficiency. The design has a variable gain reception to measure precisely the incoming signal level and obtaining signal quality indicators similar to RSSI used in wireless RF sensor networks. The circuit has been simulated and experimentally tested too with a prototype. Several tests have been carried out using the different alternatives presented. The goal of the first experiments was to characterize the frequency response of the transducers, and validate acoustic wave generation and amplification models obtained by means of simulation. Measurements were also taken to obtain receiver sensitivity and communication efficiency to power variations. Efficient design of both power amplifier and receiver analog processing stages, combined with optimal microcontroller power saving modes has extended estimated battery. As a conclusion, a worthwhile modem has been designed with the following advantages: Ultra-Low power consumption, a small form factor and a low final cost which enable future low cost deployment of underwater sensor networks.

Valproate population pharmacokinetics in children

Abstract: Summary Objective:A population analysis of the kinetics of valproic acid (VPA) in children with epilepsy was performed in order to characterize the covariates which influence VPA clearance (CL). Methods: A total of 770 steady-state serum concentration samples was analysed. These were collected during VPA therapy from 255 children, aged 0·1–14 years and weighting 4–74 kg. Age, total body weight (TBW), VPA daily dose, sex and comedication with carbamazepine (CBZ) were considered as covariates. Population analysis was made with NONMEM program, assuming a one-compartment model, fixing the VPA absorption rate, bioavailability and distribution volume at values found in the literature. The results of the population pharmacokinetics analysis were validated in a group of 45 epileptic patients. Results: The final regression model for VPA clearance, that included TBW (kg), daily dose (mg/kg) and CBZ comedication as covariates with a significant influence on this parameter, was as follows: CL (L/h) = 0·012 TBW0·715 DOSE0·306(1·359 CBZ). The coefficient of variation for interpatient variability in CL was 21·4% and the residual variability estimated was 23·9% for a concentration of 65 mg/l. In order to estimate the predictive performance of the selected final model, predictions of the VPA serum concentrations were calculated and compared with VPA measured concentrations in the validation group. This assessment revealed an important improvement in the predictive performance of VPA concentrations in comparison with the basic model that did not include any covariates (root squared mean error: 19·50 vs. 39·73 mg/l). Conclusion: A population pharmacokinetic model is proposed to estimate the individual CL for paediatric patients receiving VPA in terms of patient's dose, weight and concomitant CBZ, in order to establish a priori dosage regimens.

Underwater Sensor Networks: A New Energy Efficient and Robust Architecture

Abstract: The specific characteristics of underwater environments introduce new challenges for networking protocols. In this paper, a specialized architecture for underwater sensor networks (UWSNs) is proposed and evaluated. Experiments are conducted in order to analyze the suitability of this protocol for the subaquatic transmission medium. Moreover, different scheduling techniques are applied to the architecture in order to study their performance. In addition, given the harsh conditions of the underwater medium, different retransmission methods are combined with the scheduling techniques. Finally, simulation results illustrate the performance achievements of the proposed protocol in end-to-end delay, packet delivery ratio and energy consumption, showing that this protocol can be very suitable for the underwater medium.

Mechanism-Based Concepts of Size and Maturity in Pharmacokinetics

Abstract: Growth and development can be investigated using readily observable demographic factors such as weight and age. Size is the primary covariate and can be referenced to a 70-kg person with allometry using a coefficient of 0.75 for clearance and 1 for volume. The use of these coefficients is supported by fractal geometric concepts and observations from diverse areas in biology. Fat free mass (FFM) might be expected to do better than total body weight when there are wide variations in fat affecting body composition. Clearance pathways develop in the fetus before birth. The use of postnatal age as a descriptor of maturation is unsatisfactory because birth may occur prematurely; therefore postmenstrual age is a superior predictor of elimination function. A sigmoid E(max) model (Hill equation) describes gradual maturation of clearance in early life leading to a mature adult clearance achieved at a later age.

Exploration of underwater life with an acoustically controlled soft robotic fish

Abstract: Closeup exploration of underwater life requires new forms of interaction, using biomimetic creatures that are capable of agile swimming maneuvers, equipped with cameras, and supported by remote human operation. Current robotic prototypes do not provide adequate platforms for studying marine life in their natural habitats. This work presents the design, fabrication, control, and oceanic testing of a soft robotic fish that can swim in three dimensions to continuously record the aquatic life it is following or engaging. Using a miniaturized acoustic communication module, a diver can direct the fish by sending commands such as speed, turning angle, and dynamic vertical diving. This work builds on previous generations of robotic fish that were restricted to one plane in shallow water and lacked remote control. Experimental results gathered from tests along coral reefs in the Pacific Ocean show that the robotic fish can successfully navigate around aquatic life at depths ranging from 0 to 18 meters. Furthermore, our robotic fish exhibits a lifelike undulating tail motion enabled by a soft robotic actuator design that can potentially facilitate a more natural integration into the ocean environment. We believe that our study advances beyond what is currently achievable using traditional thruster-based and tethered autonomous underwater vehicles, demonstrating methods that can be used in the future for studying the interactions of aquatic life and ocean dynamics.

Measured Performance of a 1.72 kW Rooftop Grid Connected Photovoltaic System in Ireland

Abstract: This paper presents results obtained from monitoring a 1.72 kWp photovoltaic system installed on a flat roof of a 12 m high building in Dublin, Ireland (latitude 53.4°N and longitude 6.3°E). The system was monitored between November 2008 and October 2009 and all the electricity generated was fed into the low voltage supply to the building. Monthly average daily and annual performance parameters of the PV system evaluated include: final yield, reference yield, array yield, system losses, array capture losses, cell temperature losses, PV module efficiency, system efficiency, inverter efficiency, performance ratio and capacity factor. The maximum solar radiation, ambient temperature and PV module temperature recorded were 1241 W/m2 in March, 29.5 °C and 46.9 °C in June respectively. The annual total energy generated was 885.1 kW h/kWp while the annual average daily final yield, reference yield and array yield were 2.41 kW h/kWp/day, 2.85 kW h/kWp/day and 2.62 kW h/kWp/day respectively. The annual average daily PV module efficiency, system efficiency and inverter efficiency were 14.9%, 12.6% and 89.2% respectively while the annual average daily performance ratio and capacity factor were 81.5% and 10.1% respectively. The annual average daily system losses, capture losses and cell temperature losses were 0.23 h/day, 0.22 h/day and 0.00 h/day respectively. Comparison of this system with other systems in different locations showed that the system had the highest annual average daily PV module efficiency, system efficiency and performance ratio of 14.9%, 12.6% and 81.5% respectively. The PV system’s annual average daily final yield of 2.4 kW h/kWp/day is higher than those reported in Germany, Poland and Northern Ireland. It is comparable to results from some parts of Spain but it is lower than the reported yields in most parts of Italy and Spain. Despite low insolation levels, high average wind speeds and low ambient temperature improve Ireland’s suitability.