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

Design and implementation of integrated common mode capacitors for SiC-JFET inverters

Abstract—This paper deals with the issue of electromagnetic interference (EMI) in SiC-JFET inverter power modules, and proposes a solution to limit conducted emissions at high frequencies. SiC-JFET inverters can achieve very fast switching, thereby reducing commutation losses, at the cost of a high level of EMI. In order to limit conducted EMI emissions, it is proposed to integrate small-value common mode (CM) capacitors, directly into the power module. High frequency noise, which is usually difficult to filter, is then contained within the module, thus keeping it far from the external network. This approach is in line with the current trend towards the integration of various functions (such as protection, sensors or drivers) around power devices in modern power modules. To demonstrate this concept, the resulting CM noise was investigated, and compared with a standard configuration. Simulations were used to design the integrated capacitors, and measurements were carried out on an experimental SiC-JFET half-bridge structure. A significant reduction was achieved in the experimentally observed CM conducted emissions, with a very minor influence on the switching waveforms, losses and overall size of the system. The benefits and limitations of this design are discussed, for the case of mid-power range inverters for aircraft applications. Index Terms—Electromagnetic compatibility, Inverters, Multichip modules

Characterization of materials and their interfaces in a direct bonded copper substrate for power electronics applications

International audienceDirect Bonded Copper (DBC) are produced by high temperature (>1000 °C) bonding between copper and a ceramic (usually alumina). They are commonly used in power electronics. However, their reliability when exposed to thermal cycling is still an issue, that could be addressed by advanced numerical simulations. This paper describes the identification of the parameters for a numerical model that uses finite elements with cohesive zones. This identification is based on careful mechanical characterization of all components of the DBC (ceramic, copper and interface) using an innovative approach based on image correlation

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