Nutrient limitation can explain a rapid transition to synchrony in an upwelling-driven diatom community

Identifying the mechanisms controlling the temporal dynamics of ecological communities is key to understand their vulnerability to natural and anthropogenic impacts and to identify early warnings of critical transitions. At community level, inter-specific synchrony is an important indicator of ecosystem stability and variation in function. Using wavelet analysis on time-series of abundance of 12 dominant diatom species, sampled monthly (1994-2009) in a coastal upwelling embayment at the northern limit of the Canary Current Upwelling System, we find a sudden onset of synchrony between 1998 and 2002, concomitant with an increase in the amplitude of the upwelling index at different temporal scales. To better understand the underlying mechanism that could generate this sudden onset of synchrony among competitors, we analyzed a general model of competition between two species for two essential nutrients (e.g., nitrogen and silicate). We incorporate environmental variation by varying the concentration of one of the essential nutrients entering the system. Increase in the amplitude of environmental variation always leads to greater synchrony among competitors. This occurs because the system shifts from a state in which species are limited by different nutrients to one where species are often limited by the same nutrient. We show that the transition from asynchronous to synchronous dynamics can occur suddenly as the amplitude of environmental variation increases. While it is not possible to rule out alternative mechanisms, our model demonstrates that sudden changes in the extent of synchronization should be a common feature when species compete for essential nutrients in variable environments.En prensa3,38

A multidisciplinary approach to identify priority areas for the monitoring of a vulnerable family of fishes in Spanish Marine National Parks

Background Syngnathid fishes (Actinopterygii, Syngnathidae) are flagship species strongly associated with seaweed and seagrass habitats. Seahorses and pipefishes are highly vulnerable to anthropogenic and environmental disturbances, but most species are currently Data Deficient according to the IUCN (2019), requiring more biological and ecological research. This study provides the first insights into syngnathid populations in the two marine Spanish National Parks (PNIA—Atlantic- and PNAC—Mediterranean). Fishes were collected periodically, marked, morphologically identified, analysed for size, weight, sex and sexual maturity, and sampled for stable isotope and genetic identification. Due the scarcity of previous information, habitat characteristics were also assessed in PNIA. Results Syngnathid diversity and abundance were low, with two species identified in PNIA (Hippocampus guttulatus and Syngnathus acus) and four in PNAC (S. abaster, S. acus, S. typhle and Nerophis maculatus). Syngnathids from both National Parks (NP) differed isotopically, with much lower δ15N in PNAC than in PNIA. The dominant species were S. abaster in PNAC and S. acus in PNIA. Syngnathids preferred less exposed sites in macroalgal assemblages in PNIA and Cymodocea meadows in PNAC. The occurrence of very large specimens, the absence of small-medium sizes and the isotopic comparison with a nearby population suggest that the population of Syngnathus acus (the dominant syngnathid in PNIA) mainly comprised breeders that migrate seasonally. Mitochondrial cytochrome b sequence variants were detected for H. guttulatus, S. acus, and S. abaster, and a novel 16S rDNA haplotype was obtained in N. maculatus. Our data suggest the presence of a cryptic divergent mitochondrial lineage of Syngnathus abaster species in PNAC. Conclusions This is the first multidisciplinary approach to the study of syngnathids in Spanish marine NPs. Habitat preferences and population characteristics in both NPs differed. Further studies are needed to assess the occurrence of a species complex for S. abaster, discarding potential misidentifications of genus Syngnathus in PNAC, and evaluate migratory events in PNIA. We propose several preferential sites in both NPs for future monitoring of syngnathid populations and some recommendations for their conservation.Postprin

Integrated motor drives: state of the art and future trends

With increased need for high power density, high efficiency and high temperature capabilities in Aerospace and Automotive applications, Integrated Motor Drives (IMD) offers a potential solution. However, close physical integration of the converter and the machine may also lead to an increase in components temperature. This requires careful mechanical, structural and thermal analysis; and design of the IMD system. This paper reviews existing IMD technologies and their thermal effects on the IMD system. The effects of the power electronics (PE) position on the IMD system and its respective thermal management concepts are also investigated. The challenges faced in designing and manufacturing of an IMD along with the mechanical and structural impacts of close physical integration is also discussed and potential solutions are provided. Potential converter topologies for an IMD like the Matrix converter, 2-level Bridge, 3-level NPC and Multiphase full bridge converters are also reviewed. Wide band gap devices like SiC and GaN and their packaging in power modules for IMDs are also discussed. Power modules components and packaging technologies are also presented

Semi-passive piezoelectric noise control in transmission by synchronized switching damping on voltage source

This paper deals with the so called SSD (stands for Synchronized Switch Damping) technique that is a semi-passive approach developed to address the problem of structural vibration damping and noise reduction. Compared to standard passive piezoelectric damping, this technique offers the advantage of self-adaptation with environmental variations (e.g. temperature). On the contrary to the active damping systems, its implementation does not require any sophisticated signal processing or any bulk power. In the semi passive approach, the piezoelectric element is continuously switched from open circuit to short circuit synchronously to the strain. Due to this switching mechanism, a phase difference appears between the strain induced by an incident acoustic wave and the resulting voltage, thus creating energy dissipation. With the non-linear process, damping performances directly depend on the electromechanical coupling coefficient of the system. For the weakly coefficient coupling systems, the voltage amplitude of the piezoelectric elements can be artificially increased by switching on voltage sources. Using this new method SSDV (stands for Synchronized Switch Damping on Voltage source), 16.1 dB attenuation on the transmitted wave pressure in the tube is obtained whereas only 8 dB were achieved with the classical SSDI (stands for Synchronized Switch Damping on Inductor). Furthermore, as this method is adaptive, attenuation is observed over a 600 Hz-wide frequency band

Shift in seasonal amplitude and synchronicity of zooplankton in the northwest Iberian shelf driven by meteo-hydrographic forcing

We have investigated zooplankton temporal dynamics in the northwest Iberian shelf, a temperate ecosystem subject to coastal upwelling-donnwelling processes. To this aim, we have applied wavelet analysis, a methodology able to cope with non-stationary dynamics, to monthly time series of zooplankton abundance and biomass acquired between 1995 and 2011 at two locations over the shelf and to environmental variables known to affect functioning of this ecosystem (wind regime, Ekam transport and river outflows). The seasonal signal of total zooplankton abundance and of the main taxonomic groups showed an abrupt increase in amplitude around 2001 that persisted until the end of the series in 2011. Concurrent with the change in amplitude, there was a synchronization of the seasonal cycle of abundance among taxonomics groups (e.g. copepods, larvaceans, chaetognats...) and copepod species, which persisted for several years although it decreased at the end of the series. Between 2001 and 2004, significant changes in wind regime patterns, linked to variability of the North Atlantic Oscillation, were observed: westerly winds became predominant, river outflow increased and offshore Ekman transport decreased. This meteo-climatic configuration favors retention mechanisms over across-shelf exchage processes due to the reinforcement of the western Iberian buoyant plume (WIBP) and the prevalence of downwelling. We hypothesized that the observed changes in zooplankton dynamics are governed by the amplification of the seasonal signal of these environmental drivers causing enhancement of the retention phenomena

Mesozooplankton dynamics along the Northwest and north Iberian Shelf.

Within the framework of the RADIALES time series monitoring program carried out by the Instituto Español de Oceanografía (IEO), 10 stations were monthly sampled for zooplankton biomass, abundance and taxonomic composition. Additionally, hydrographic features and nutrient concentrations were also measured. From the beginning of the program, a total of 2179 zooplankton samples have been collected. The sampling stations are located along four coastal-ocean sections in the Northwest and North Iberian shelf, off Vigo, A Coruña, Gijón and Santander beginning in 1994, 1991, 2001, 1992, respectively. There is classically a contrasted situation between the Galician and the Cantabrian coast. Since the Galician coast represents the northern limit of the Canary upwelling system, coastal upwelling has a major influence on their hydrodynamic behavior and nutrient distributions. In the Cantabrian coast, upwelling is restricted to occasional events during summer and nutrient fertilization depends mostly on the deep convection occurring during winter. In this communication we aim to describe the long-term dynamics of zooplankton biomass for oceanic and shelf waters of the northwest and north Iberian Peninsula focusing in the common period sampled in all the stations (2001-2013, representing 1405 sampling events). We used a method able to cope with the non-stationary nature of the data, namely wavelet analysis. It allows describing the periodic components of the signal as classically obtained with the Fourier analysis. But in addition, the wavelet analysis approach provides information of the variability of the periodic components along the time series. Indeed the principal periodic components (1, 1,5 and 3 years) appear to be transient in both hydrologic and zooplankton biomass series. A pair-wise comparison between the power spectrum matrices of each zooplankton biomass time series allowed us to detect common dynamics between the coastal Cantabrian stations, the oceanic Cantabrian stations and the Galician ones