A current‐mode 1kHz/10kHz low‐voltage integrated analogue PLL for lock‐in portable applications

We present a low‐supply voltage (2V) low‐power consumption (500W) analogue phase‐locked loop (PLL), working at two low frequencies (1 and 10kHz), to be used in an integrated lock‐in amplifier. An externally settable control bit allows the switching operation between the two different frequencies. The circuit has been designed in a standard 0.6–m CMOS technology and differs from the standard analogue PLL architectures for the current mode implementation of both the loop filter and of the oscillator. Three different locked waveforms (sinusoidal, triangular, squared) can be obtained at the PLL output. Simulation results, obtained through the use of PSPICE and using accurate transistor models, will be proposed. The pull‐in ranges are about ±250Hz around 1 and ±1.3kHz around 10kHz, with pull‐in times of about 10 and 4ms, respectively. Copyright © 2003 John Wiley & Sons, Ltd.     

Design and evaluation of a multimedia storage server for mixed traffic

The relative simplicity of access to digital communications nowadays and the simultaneous increase in the available bandwidth are leading to the definition of new telematic services, mainly oriented towards multimedia applications and interactivity with the user. In the near future, a decisive role will be played in this scenario by the providers of interactive multimedia services of the on-demand type, which will guarantee the end user a high degree of flexibility, speed and efficiency. In this paper, some of the technical aspects regarding these service providers are dealt with, paying particular attention to the problems of storing information and managing service requests. More specifically, the paper presents and evaluates a new storage technique based on the use of disk array technology, which can manage both typical multimedia connections and traditional requests. The proposed architecture is based on the joint use of the partial dynamic declustering and the information dispersal algorithm, which are employed for the allocation and retrieval of the data stored on the disk array. We also define efficient strategies for request management in such a way as to meet the time constraints imposed by multimedia sessions and guarantee good response times for the rest of the traffic. The system proposed is then analyzed using a simulation approach.     

An Attempt at the Classification of Energy Decaying Schemes for Structural and Multibody Dynamics

This paper analyzes the formulation of energy preserving/decaying schemes for dynamics problems. We argue that any energy preserving/decaying scheme can always be seen as composed of an underlying temporal discretization, that is then slightly modified in order to prove a discrete energy bound within a time step. While the details of the modified scheme depend in a critical way on the governing equations, the underlying discretization can in principle be applied to a variety of models. We review some of the temporal underlying schemes recently proposed in the literature, presenting them with a common notation. We show their similarities and highlight their differences.     

Implicit fault-tolerant control: application to induction motors

In this paper we propose an innovative way of dealing with the design of fault-tolerant control systems. We show how the nonlinear output regulation theory can be successfully adopted in order to design a regulator able to offset the effect of all possible faults which can occur and, in doing so, also to detect and isolate the occurred fault. The regulator is designed by embedding the (possible nonlinear) internal model of the fault. This idea is applied to the design of a fault-tolerant controller for induction motors in presence of both rotor and stator mechanical faults.     

Modelling observed California Current mesoscale eddies and the ecosystem response

Satellite and in situ observations are used to test model dynamics for the California Current System (CCS). The model and data are combined to reconstruct the mesoscale ocean structure during a given three-week period. The resulting physical flow field is used to drive a 3D ecosystem model to interpret SeaWiFS and in situ chlorophyll-a (chl-a) variations. With this approach a more complete and consistent picture of the physical and ecosystem processes of the CCS is obtained, providing the basis for addressing fundamental questions about dynamics and predictability of the coastal ocean.     

Enhanced automatic detection of human settlements using Sentinel-1 interferometric coherence

This article presents an experiment in which multi-temporal interferometric coherence calculated from 6-days Sentinel-1A and Sentinel-1B image pairs and backscatter intensity σ° are jointly used for the extraction of built-up areas in the framework of the symbolic machine learning classification. The results obtained with the proposed approach confirm the enhanced capabilities of discriminating built-up areas when using coherence information in comparison to two available global human settlement layers derived: (1) from Landsat optical data and (2) from Sentinel-1 ground range detected data and based on backscatter intensity σ° only. The experiment carried out in The Netherlands Randstad area is expected to be indicative of the results obtainable for urban areas having similar structures and types of built-up.     

Matched disturbance suppression for nonlinear systems stabilizable by logic-based feedback

We focus on a class of nonlinear systems that can be stabilized at a desired compact set by means of logic-based continuous feedback and we show how to design regulators that are robust to matched exosystem-generated disturbances. The proposed design methodology, of interest also for purely continuous-time systems, combines recent advances in the field of hybrid control systems and output regulation for nonlinear systems. As an illustrative example, the problem of global stabilization of a 6-DOF rigid body affected by a force periodic disturbance of uncertain amplitude, phase and frequency is presented.     

Evaluation of decay photocurrent measurements in dye‐sensitized solar cells: Application to laser beam‐induced current technique

The use of the laser beam‐induced current (LBIC) technique in photovoltaic devices is widespread, but its use in photoelectrochemical cells, such as dye‐sensitized solar cells (DSSCs), is limited due to the configuration of these devices. The main reason is the very slow response time of DSSCs in the decay process, and therefore LBIC scans take too long to perform. We have designed a procedure published in the literature to correct the photocurrent values obtained by the LBIC technique, based on an algorithm that uses a decreasing mono‐exponential model. This work presents a study of the decay measurements in DSSCs using several functions, in order to improve the algorithm designed. It concludes that functions such as a decreasing bi‐exponential or Becquerel function generate better fits to experimental data. Copyright © 2010 John Wiley & Sons, Ltd.