The M waves of the biceps brachii have a stationary (shoulder-like) component in the first phase: Implications and recommendations for M-wave analysis

Objective. We recently documented that compound muscle action potentials (M waves) recorded over the 'pennate' vastus lateralis showed a sharp deflection (named as a shoulder) in the first phase. Here, we investigated whether such a shoulder was also present in M waves evoked in a muscle with different architecture, such as the biceps brachii, with the purpose of elucidating the electrical origin of such afeature. Approach. M waves evoked by maximal single shocks to the brachial plexus were recorded in monopolar and bipolar configurations from 72 individuals using large (10 mm diameter) electrodes and from eight individuals using small (1 mm diameter) electrodes arranged in a linear array. The changes in M-wave features at different locations along the muscle fiber direction were examined. Main results. The shoulder was recognizable in most (87%) monopolar M waves, whereas it was rarely observed (6%) in bipolar derivations. Recordings made along the fiber direction showed that the shoulder was a stationary (non-propagating) feature, with short duration (spiky), which had positive polarity at all locations along the fibers. The latency of the shoulder (9.5 ± 0.5 ms) was significantly shorter than the estimated time taken for the action potentials to reach the biceps tendon (12.8 ms). Significance. The shoulder must be generated by a dipole source, i.e. a source created at a fixed anatomical position, although the exact origin of this dipole is uncertain. Our results suggest that the shoulder may not be due to the end-of-fiber signals formed at the biceps brachii tendon. The shoulder is not related to any specific arrangement of muscle fibers, as it has been observed in both pennate and fusiform muscles. Being a stationary (non-propagating) component, the shoulder is not reliable for studying changes in sarcolemmal excitability, and thus should be excluded from the M-wave analysis

Unraveling the Contribution of Turbulence and Bubbles to Air-Water Gas Exchange in Running Waters

Quantifying air-water gas exchange is critical for estimating greenhouse gas fluxes and metabolism in aquatic ecosystems. In high-energy streams, the gas exchange rate k is poorly constrained, due to an incomplete understanding of turbulence and bubble contributions to k. We performed a flume experiment with air bubble additions to evaluate the combined effects of turbulence and bubbles on k for helium, argon, xenon, and methane. We created contrasting hydraulic conditions by varying channel slope, bed roughness, water discharge, and bubble flux. We found that k increased from 1-4 to 17-66 m d(-1) with increases in turbulence and bubble flux metrics. Mechanistic models that explicitly account for these metrics, as well as gas diffusivity and solubility, agreed well with the data and indicated that bubble-mediated gas exchange accounted for 64-93% of k. Bubble contributions increased with bubble flux but were independent of gas type, as bubbles did not equilibrate with the water. This was evident through modeled bubble life and equilibration times inferred from bubble size distributions obtained from underwater sound spectra. Sound spectral properties correlated well with turbulence and bubble flux metrics. Our results demonstrate that (a) mechanistic models can be applied to separate free surface- and bubble-mediated gas exchange in running waters, (b) bubble life and equilibration times are critical for accurate scaling of k between different gases, and (c) ambient sound spectra can be used to approximate contributions of turbulence and bubbles

Storage selection functions: A coherent framework for quantifying how catchments store and release water and solutes

We discuss a recent theoretical approach combining catchment-scale flow and transport processes into a unified framework. The approach is designed to characterize the hydrochemistry of hydrologic systems and to meet the challenges posed by empirical evidence. StorAge Selection functions (SAS) are defined to represent the way catchment storage supplies the outflows with water of different ages, thus regulating the chemical composition of out-fluxes. Biogeochemical processes are also reflected in the evolving residence time distribution and thus in age-selection. Here we make the case for the routine use of SAS functions and look forward to areas where further research is needed

Gravity and low pressure die casting of aluminium alloys: a technical and economical benchmark

Among the innovative and conventional foundry processes for Aluminium alloys, low pressure die casting is characterised by several advantages, including high yield, excellent control of operative parameters, good metallurgical and technological quality. This process is often (and incorrectly) associated only to the production of automotive wheels, while it is improving its potential both towards other automotive components and non-automotive parts. The paper is aimed at showing the potential of low pressure die casting for the production of safety boxes, to be employed in chemical, petrol and off-shore plants. This potential is examined both in technical and economical terms, and is compared with that offered by other conventional Aluminium foundry processes, such as permament mould gravity diecasting

Dynamic spatio-temporal patterns of metapopulation occupancy in patchy habitats

Spatio-temporal dynamics in habitat suitability and connectivity among mosaics of heterogeneous wetlands are critical for biological diversity and species persistence in aquatic patchy landscapes. Despite the recognized importance of stochastic hydroclimatic forcing in driving wetlandscape hydrological dynamics, linking such effects to emergent dynamics of metapopulation poses significant challenges. To fill this gap, we propose here a dynamic stochastic patch occupancy model (SPOM), which links parsimonious hydrological and ecological models to simulate spatio-temporal patterns in species occupancy in wetlandscapes. Our work aims to place ecological studies of patchy habitats into a proper hydrologic and climatic framework to improve the knowledge about metapopulation shifts in response to climate-driven changes in wetlandscapes. We applied the dynamic version of the SPOM (D-SPOM) framework in two wetlandscapes in the US with contrasting landscape and climate properties. Our results illustrate that explicit consideration of the temporal dimension proposed in the D-SPOM is important to interpret local- A nd landscape-scale patterns of habitat suitability and metapopulation occupancy. Our analyses show that spatio-temporal dynamics of patch suitability and accessibility, driven by the stochasticity in hydroclimatic forcing, influence metapopulation occupancy and the topological metrics of the emergent wetlandscape dispersal network. D-SPOM simulations also reveal that the extinction risk in dynamic wetlandscapes is exacerbated by extended dry periods when suitable habitat decreases, hence limiting successful patch colonization and exacerbating metapopulation extinction risks. The proposed framework is not restricted only to wetland studies but could also be applied to examine metapopulation dynamics in other types of patchy habitats subjected to stochastic external disturbances

Response of estuarine meiofauna assemblage to effects of fertilizer enrichment used in the sugar cane monoculture. Pernambuco, Brazil

A aplicação in situ de fertilizantes inorgânicos foi utilizada para simular a eutrofização associada ao cultivo da cana-de-açúcar. A estrutura da associação de meiofauna foi analisada com o objetivo de avaliar este impacto. O experimento de enriquecimento do sedimento foi desenvolvido em nove áreas quadrangulares de 4m² distribuídas de forma aleatória no mediolitoral da área estuarina. Três áreas foram enriquecidas com alta concentração (375 g/m²) de NPK (Nitrogênio-Fósforo-Potássio), três com baixa concentração (187,5 g/m²) e as demais tratadas como controle. Os fertilizantes foram aplicados semanalmente. Os parâmetros físico-químicos do sedimento e a meiofauna bentônica foram coletados após três a quatro semanas da aplicação dos fertilizantes. Obedecendo este intervalo foram realizadas 6 amostragens subseqüentes. As amostras foram triadas e a meiofauna contada e identificada em nível de grande grupo. As respostas da meiofauna variaram de acordo com a área: enquanto a área Controle manteve sua abundância total durante todo o experimento, as áreas tratadas apresentaram forte queda nas densidades totais. A ordenação MDS e a análise ANOSIM evidenciaram mudanças significativas na estrutura da associação de meiofauna entre as áreas e também ao longo do experimento nas áreas tratadas.In situ application of inorganic fertilizer was used to simulate environmental eutrophication associated with the sugar cane monoculture. Meiofauna community structure is herein used to assess this experimental impact. Nine quadrangular areas (4m² each) were randomly defined in the midlittoral estuarine area. Three of these areas received a high dose of sugar cane fertilizer (375 g/m² Nitrogen-Phosphorus-Potassium), three areas received a low dose of the fertilizer (187.5 g/m²) and the other three areas represented the control. The fertilizer was applied every week. Environmental parameters and meiofauna were sampled using three-to-four week intervals. Six samplings were subsequently performed maintaining this interval. Meiofauna was counted and identified to major taxonomic groups. Meiofauna community structure varied throughout the experimental areas. Control areas maintained their abundance values during the study period, but within the enriched areas meiofauna abundance decreased greatly. MDS and ANOSIM analysis showed significant variation in the meiofauna community structure among experimental areas and also along the experimental period in the enriched areas

Relationship of morpho-sedimentological variations to the fate of Hg- and Zn-polluted sediments in the contaminated site of Porto Marghera, Lagoon of Venice, Italy.

New data collected from twenty-six sites during 2008 in the contaminated Site of National Interest (SIN) of Porto Mar- ghera within the Lagoon of Venice (Italy), which has been affected by the presence of an industrial zone for the last 80 years, were compared with data from a campaign performed in the same site 30 years before (1976-1978). The SIN was found to be heavily polluted in the earlier study, and several tons of Hg and Zn are still stored in soils and industrial channel sediments, potentially affecting the lagoon part of the SIN. Bathymetric variations, grain-size, Hg and Zn con- tent in sediments were analysed. The severe contamination of the late 1970s (Hg 1.7 µg/g; Zn 754 µg/g) had fallen by the late 2000s (Hg 0.9 µg/g; Zn 225 µg/g). The fall in Hg and Zn contamination over the 30-year period was mainly linked to the patterns of geomorphological change inside the SIN that affected two distinct sub-areas: 1) a stable-depo- sitional (SD) area in the Northern part, which exerted a “dilution” effect on contaminants, with significant deposition (~11%) of coarse-grained sediments (63 - 8 µm), and 2) an area characterised by moderate-to-severe-erosion (MSE) to the South, which saw the loss (~13%) of pollutant-bearing fine-grained sediments (<8 µm). A budget calculation in the MSE sub-area showed a loss of ~2.5 tons for Hg and ~700 tons for Zn over three decades, most of which was exported to other parts of the LV or at the open sea. A similar amount is still stored in the SD area, which will be subject to ero- sion if hydrodynamic conditions change in the future. This study provides useful support to decision-making systems by helping to select hot-spots for remediation measures