Francesc Oliva

Feature Extraction for Multi-class BCI using Canonical Variates Analysis

To propose a new feature extraction method with canonical solution for multi-class brain-computer interfaces (BCI). The proposed method should provide a reduced number of canonical discriminant spatial patterns (CDSP) and rank the channels sorted by power discriminability (DP) between classes. The feature extractor relays in canonical variates analysis (CVA) which provides the CDSP between the classes. The number of CDSP is equal to the number of classes minus one. We analyze EEG data recorded with 64 electrodes from 4 subjects recorded in 20 sessions. They were asked to execute twice in each session three different mental tasks (left hand imagination movement, rest, and words association) during 7 seconds. A ranking of electrodes sorted by power discriminability between classes and the CDSP were computed. After splitting data in training and test sets, we compared the classification accuracy achieved by linear discriminant analysis (LDA) in frequency and temporal domains. The average LDA classification accuracies over the four subjects using CVA on both domains are equivalent (57.89% in frequency domain and 59.43% in temporal domain). These results, in terms of classification accuracies, are also reflected in the similarity between the ranking of relevant channels in both domains. CVA is a simple feature extractor with canonical solution useful for multi-class BCI applications that can work on temporal or frequency domain.

Using mental tasks transitions detection to improve spontaneous mental activity classification

This paper presents an algorithm based on canonical variates transformation (CVT) and distance based discriminant analysis (DBDA) combined with a mental tasks transitions detector (MTTD) to classify spontaneous mental activities in order to operate a brain-computer interface working under an asynchronous protocol. The algorithm won the BCI Competition III -Data Set V: Multiclass Problem, Continous EEG- achieving an averaged classification accuracy over three subjects of 68.65% (79.60, 70.31 and 56.02%, respectively) in a three-class problem.

Assessing species diagnostic value in large data sets: A comparison between phi-coefficient and Ochiai index

Abstract Question: Diagnostic species are useful tools for the identification and ecological interpretation of community types. Vegetation databases facilitate the computation of diagnostic values of regional validity, but it is essential to understand the behaviour of fidelity measures in large data sets. Methods: We focused our study on the phi-coefficient (Φ) of association and its limit value, the Ochiai index. The northeast Spanish relevé database was stratified using an arbitrary distance threshold in species composition. Diagnostic species analysis was undertaken using three methods of context selection: I. within a syntaxon of higher rank; II. including relevés with similar composition to that of the target unit; III. using the entire stratified database. Species diagnostic values were computed as well as bootstrap percentile confidence intervals. Results: Many species deemed as diagnostic by method I have their optima in vegetation types neighbouring the unit chosen as context. In contrast, method II excluded many of these species. Φ-values and confidence intervals were similar to those obtained by the Ochiai indexwhen using a large dataset (method III) but this similarity was greater for low level syntaxa. Conclusions: The diagnostic value of species in a given region is best assessed using the Ochiai index, since it can be split into two interpretable asymmetrical components. We recommend the determination of context-dependent differential species using the Φ-coefficient, and the assessment of species regional diagnostic value by means of a stratification procedure in combination with the Ochiai index. Nomenclature: Bolòs et al. (1990).

A multifactorial anti-cachectic approach for cancer cachexia in a rat model undergoing chemotherapy

The effectiveness of drugs aimed at counteracting cancer cachexia is generally tested in pre‐clinical rodent models, where only the tumour‐induced alterations are taken into account, excluding the co‐presence of anti‐tumour molecules that could worsen the scenario and/or interfere with the treatment.

Effects of water flow regulation on ecosystem functioning in a Mediterranean river network assessed by wood decomposition

Mediterranean rivers are extensively modified by flow regulation practises along their courses. An important part of the river impoundment in this area is related to the presence of small dams constructed mainly for water abstraction purposes. These projects drastically modified the ecosystem morphology, transforming lotic into lentic reaches and increasing their alternation along the river. Hydro-morphologial differences between these reaches indicate that flow regulation can trigger important changes in the ecosystem functioning. Decomposition of organic matter is an integrative process and this complexity makes it a good indicator of changes in the ecosystem. The aim of this study was to assess the effect caused by flow regulation on ecosystem functioning at the river network scale, using wood decomposition as a functional indicator. We studied the mass loss from wood sticks during three months in different lotic and lentic reaches located along a Mediterranean river basin, in both winter and summer. Additionally, we identified the environmental factors affecting decomposition rates along the river orders. The results revealed differences in decomposition rates between sites in both seasons that were principally related to the differences between stream orders. The rates were mainly related to temperature, nutrient concentrations (NO2(-), NO3(2-)) and water residence time. High-order streams with higher temperature and nutrient concentrations exhibited higher decomposition rates compared with low-order streams. The effect of the flow regulation on the decomposition rates only appeared to be significant in high orders, especially in winter, when the hydrological characteristics of lotic and lentic habitats widely varied. Lotic reaches with lower water residence time exhibited greater decomposition rates compared with lentic reaches probably due to more physical abrasion and differences in the microbial assemblages. Overall, our study revealed that in high orders the reduction of flow caused by flow regulation affects the wood decomposition indicating changes in ecosystem functioning.

Antifouling activity in some benthic Antarctic invertebrates by "in situ" experiments at Deception Island, Antarctica.

Competition for space is a remarkable ecological force, comparable to predation, producing a strong selective pressure on benthic invertebrates. Some invertebrates, thus, possess antimicrobial compounds to reduce surface bacterial growth. Antimicrobial inhibition is the first step in avoiding being overgrown by other organisms, which may have a negative impact in feeding, respiration, reproduction … The in situ inhibition of bacterial biofilm was used here as an indicator of antifouling activity by testing hydrophilic extracts of twelve Antarctic invertebrates. Using two different approaches (genetics and confocal techniques) different levels of activity were found in the tested organisms. In fact, differences within body parts of the studied organisms were determined, in agreement with the Optimal Defense Theory. Eight out of 15 extracts tested had negative effects on fouling after 28 days submerged in Antarctic waters. Thus, although chemical defenses may be quite species-specific in their ecological roles, these results suggest that different chemical strategies exist to deal with space competition.

Flagellar Sensillar Equipment of Two Morphologically Closely Related Aphid Hyperparasitoids (Hymenoptera: Figitidae: Alloxysta)

The antennal sensillar equipment in the parasitic wasp family Figitidae was analyzed to date only in few species, despite some are associated with crop pests and can have an economic importance. It is the case of the genus Alloxysta, which includes hyperparasitoids of aphids which can potentially reduce effectiveness of primary pest parasitoids. Here we analyzed, through scanning electron microscopy, the diversity, morphology, and distribution of the antennal sensilla in males and females of Alloxysta consobrina (Zetterstedt) and Alloxysta victrix (Westwood), two species with overall very similar morphology. In both species, antennae are filiform and cylindrical, and flagellum was longer in A. victrix. Eight sensillar types have been recognized: four types of sensilla trichoidea (ST-A, ST-B, ST-C, ST-D), sensilla coeloconica, sensilla placoidea, sensilla campaniformia, and sensilla basiconica. ST-A, ST-B, ST-C, and sensilla placoidea were the most abundant types on the antennae and often increased in number and decreased in size toward the tip of antenna. The two species seem to have several differences in their sensillar equipment, possibly in accordance with the different degree of host range. On the other hand, sexual dimorphism is probably due to the different stimuli that have to be correctly processed. The comparison with the other species of Figitidae studied by far showed, at subfamily-level, that variability in sensillar equipment and phylogeny do not agree. This suggests a complex series of morphological changes during evolution of this group. The taxonomic sample should be thus substantially enlarged to disclose possible trends in sensillar equipment evolution in the family.

A Rat Immobilization Model Based on Cage Volume Reduction: A Physiological Model for Bed Rest?

Bed rest has been an established treatment in the past prescribed for critically illness or convalescing patients, in order to preserve their body metabolic resource, to prevent serious complications and to support their rapid path to recovery. However, it has been reported that prolonged bed rest can have detrimental consequences that may delay or prevent the recovery from clinical illness. In order to study disuse-induced changes in muscle and bone, as observed during prolonged bed rest in humans, an innovative new model of muscle disuse for rodents is presented. Basically, the animals are confined to a reduced space designed to restrict their locomotion movements and allow them to drink and eat easily, without generating physical stress. The animals were immobilized for either 7, 14, or 28 days. The immobilization procedure induced a significant decrease of food intake, both at 14 and 28 days of immobilization. The reduced food intake was not a consequence of a stress condition induced by the model since plasma corticosterone levels –an indicator of a stress response– were not altered following the immobilization period. The animals showed a significant decrease in soleus muscle mass, grip force and cross-sectional area (a measure of fiber size), together with a decrease in bone mineral density. The present model may potentially serve to investigate the effects of bed-rest in pathological states characterized by a catabolic condition, such as diabetes or cancer.

The role of abiotic and biotic factors in functional structure and processes of alpine subshrub communities

Species occurrence is subjected to the particular ecological constraints of each site where species that can become dominant exert strong influence on community structure and functioning. Given the harsh environmental conditions in alpine areas and the low number of woody species able to support them, we wanted to study the effect of the main abiotic (environmental conditions related to topographical situation and bedrock type) and biotic (functional type of the dominant species) factors on functional structure and processes of alpine subshrub communities. In 24 study sites, we collected aboveground biomass and raw litter. Biomass was sorted into functional groups (shrubs, graminoids, forbs, bryophytes, lichens), which, in turn, were separated into photosynthetic and structural compartments. We characterized community structure in terms of biomass allocation of functional groups, estimated leaf primary production and litter persistence, and performed analyses of variance for each of the factors considered. Our results showed that community structure is driven mainly by the functional type of the dominant species, although abiotic factors are also relevant. Production depends on abiotic conditions. It is constrained by low temperatures in northern exposures and by low water availability in permeable bedrock types. Litter decomposition depends on environmental conditions and the dominant species characteristics. It is limited by dry conditions in southern slopes and by the thick and N-poor leaves of evergreen subshrubs. In summary, the few alpine woody species able to build specific communities in the Pyrenees grow in particular topographical situations, where they become crucial drivers of ecosystem structure and functioning.

Trend Assessment for Groundwater Pollutants: A Brief Review and Some Remarks

Groundwater is a valuable natural resource that needs to be assessed and protected. The European Union (EU) adopted new water legislation that includes the Water Framework Directive (WFD) and the Groundwater Daughter Directive (GWD). Both require the identification of sustained increasing pollution trends and their reversal. This is the second pillar of the WFD: such trends have to be identified for any pollutants that result in groundwater being characterized as at risk of not meeting the environmental objectives. Measuring these trends is necessary to determine and understand whether changes in land use, fertilizer application, pollution history, or climate change are affecting groundwater quality. However, in many cases, groundwater data series may not meet minimum requirements for classical statistical procedures employed in trend assessment: among other obstacles, data may be sparse, with missing or extreme values, censored data, seasonal effects, and autocorrelation. The aim of this chapter is to present and review several statistical methodologies that have been proposed and applied in recent years to deal with groundwater trend assessment, discussing the relative advantages and disadvantages of each one.