A semidefinite relaxation procedure for fault-tolerant observer design

A fault-tolerant observer design methodology is proposed. The aim is to guarantee a minimum level of closed-loop performance under all possible sensor fault combinations while optimizing performance under the nominal, fault-free condition. A novel approach is proposed to tackle the combinatorial nature of the problem, which is computationally intractable even for a moderate number of sensors, by recasting the problem as a robust performance problem, where the uncertainty set is composed of all combinations of a set of binary variables. A procedure based on an elimination lemma and an extension of a semidefinite relaxation procedure for binary variables is then used to derive sufficient conditions (necessary and sufficient in the case of one binary variable) for the solution of the problem which significantly reduces the number of matrix inequalities needed to solve the problem. The procedure is illustrated by considering a fault-tolerant observer switching scheme in which the observer outputs track the actual sensor fault condition. A numerical example from an electric power application is presented to illustrate the effectiveness of the design

Relay synchronization in multiplex networks

Relay (or remote) synchronization between two not directly connected oscillators in a network is an important feature allowing distant coordination. In this work, we report a systematic study of this phenomenon in multiplex networks, where inter-layer synchronization occurs between distant layers mediated by a relay layer that acts as a transmitter. We show that this transmission can be extended to higher order relay configurations, provided symmetry conditions are preserved. By first order perturbative analysis, we identify the dynamical and topological dependencies of relay synchronization in a multiplex. We find that the relay synchronization threshold is considerably reduced in a multiplex configuration, and that such synchronous state is mostly supported by the lower degree nodes of the outer layers, while hubs can be de-multiplexed without affecting overall coherence. Finally, we experimentally validated the analytical and numerical findings by means of a multiplex of three layers of electronic circuits.the analytical and numerical findings by means of a multiplex of three layers of electronic circuits

Galaxy clustering with photometric surveys using PDF redshift information

Photometric surveys produce large-area maps of the galaxy distribution, but with less accurate redshift information than is obtained from spectroscopic methods. Modern photometric redshift (photo-z) algorithms use galaxy magnitudes, or colors, that are obtained through multi-band imaging to produce a probability density function (PDF) for each galaxy in the map. We used simulated data to study the effect of using different photo-z estimators to assign galaxies to redshift bins in order to compare their effects on angular clustering and galaxy bias measurements. We found that if we use the entire PDF, rather than a single-point (mean or mode) estimate, the deviations are less biased, especially when using narrow redshift bins. When the redshift bin widths are $\Delta z=0.1$, the use of the entire PDF reduces the typical measurement bias from 5%, when using single point estimates, to 3%.Comment: Matches the MNRAS published version. 19 pages, 19 Figure

Negotiation of meaning via virtual exchange in immersive virtual reality environments

This study examines how English-as-lingua-franca (ELF) learners employ semiotic resources, including head movements, gestures, facial expression, body posture, and spatial juxtaposition, to negotiate for meaning in an immersive virtual reality (VR) environment. Ten ELF learners participated in a Taiwan-Spain VR virtual exchange project and completed two VR tasks on an immersive VR platform. Multiple datasets, including the recordings of VR sessions, pre- and post-task questionnaires, observation notes, and stimulated recall interviews, were analyzed quantitatively and qualitatively with triangulation. Built upon multimodal interaction analysis (Norris, 2004) and Varonis and Gass’ (1985a) negotiation of meaning model, the findings indicate that ELF learners utilized different embodied semiotic resources in constructing and negotiating meaning at all primes to achieve effective communication in an immersive VR space. The avatar-mediated representations and semiotic modalities were shown to facilitate indication, comprehension, and explanation to signal and resolve non-understanding instances. The findings show that with space proxemics and object handling as the two distinct features of VR-supported environments, VR platforms transform learners’ social interaction from plane to three-dimensional communication, and from verbal to embodied, which promotes embodied learning. VR thus serves as a powerful immersive interactive environment for ELF learners from distant locations to be engaged in situated languacultural practices that goes beyond physical space. Pedagogical implications are discussed

Immigració, immersió en català i rendiment escolar: dos estudis revisats

Després de repassar, aportant-hi dades empíriques, que la llengua del país és la porta d'entrada dels immigrants a la societat receptora, són revistats dos estudis sobre el reeiximent acadèmic i la immersió en català. El primer estudi examina els expedients acadèmics d'una escola vallesana d'educació general bàsica (EGB) des de set anys abans de la Llei del català del 1983 fins al curs 1983-1984. El segon és una enquesta sobre adaptació al país a estudiants de diversos instituts de les Balears, ja sota el règim de la Llei de normalització del català a les Balears del 1986. En ambdós casos hom relaciona els resultats acadèmics en funció de la llengua familiar (català o castellà) o dels indicadors d'integració. Com a conclusions: 1) L'adquisició de la llengua catalana no compleix una simple funció comunicativa sinó que principalment facilita l'adquisició de la cultura subjectiva del país. 2) La immersió escolar en català millora, com més va, més, els rendiments dels infants d'immigrants de la resta d'Espanya. 3) El progrés acadèmic, en instituts balears de secundària, està relacionat positivament i significativa amb l'ús de la llengua catalana i amb la integració dels alumnes a la cultura subjectiva del país.After considering, with the provision of empirical facts, the assertion that a country's language is the gateway to the host society for immigrants, two research studies on academic success and Catalan language are reviewed. The first study deals with the academic records in a primary school in the Vallès region in the period extending from seven years before the enactment of the Catalan Language Law of 1983 up to the school year 1983-1984. The second study is a survey among students from different Balearic secondary schools on their adaptation to the country during the period under the Catalan Normalisation Law of the Balearic Islands enacted in 1986. In both cases the academic results are presented on the basis of the mother tongue (Catalan or Spanish) or of integration indicators. The following conclusions are reached: 1) The acquisition of the Catalan language has not a mere communicative function but above all it facilitates the acquisition of the subjective culture of the country. 2) Increased Catalan language immersion at school improves proportionally the academic results of the children of Spanish immigrants. 3) School progress, in Balearic high schools, is positively and significantly correlated to the use of the Catalan language and to students' integration into the subjective culture of the country

Explosive first-order transition to synchrony in networked chaotic oscillators

Critical phenomena in complex networks, and the emergence of dynamical abrupt transitions in the macroscopic state of the system are currently a subject of the outmost interest. We report evidence of an explosive phase synchronization in networks of chaotic units. Namely, by means of both extensive simulations of networks made up of chaotic units, and validation with an experiment of electronic circuits in a star configuration, we demonstrate the existence of a first order transition towards synchronization of the phases of the networked units. Our findings constitute the first prove of this kind of synchronization in practice, thus opening the path to its use in real-world applications.Comment: Phys. Rev. Lett. in pres

Fault-tolerant Wide-area Control for Power Oscillation Damping

The effectiveness of using both local and remote (wide-area) feedback signals for power oscillation damping (POD) controllers is first demonstrated. The challenge is then to guarantee a minimum level of dynamic performance with only the local signals following a sudden loss of remote signals. A case study on the Nordic equivalent system is presented to show that the closed-loop response could deteriorate if the remote signals are lost. A fault-tolerant control (FTC) design methodology is presented to solve this problem and ensure an acceptable performance level even in case of loss of remote signals. The FTC design methodology is based on simultaneous regional pole-placement for normal and loss of (remote) signals conditions. First the problem is solved non-iteratively using a Linear Matrix Inequality (LMI) approximation and then it is shown that, although this procedure is linear and easy to implement, it has a drawback: the value of one of the control matrices is fixed before calculating the others. An iterative procedure is presented instead to ameliorate this problem and potentially improve the damping of the system. Case studies on the Nordic equivalent system confirm that the proposed iterative fault tolerant controller (FTCit) is able to improve performance against the non-iterative fault tolerant controller (FTC) and produce acceptable performance in case of loss of the remote signals while the response with a CC is unacceptable if a fault occurs