High temperature magnetic stabilization of cobalt nanoparticles by an antiferromagnetic proximity effect

Thermal activation tends to destroy the magnetic stability of small magnetic nanoparticles, with crucial implications in ultra-high density recording among other applications. Here we demonstrate that low blocking temperature ferromagnetic (FM) Co nanoparticles (TB<70 K) become magnetically stable above 400 K when embedded in a high N\'eel temperature antiferromagnetic (AFM) NiO matrix. The origin of this remarkable TB enhancement is due to a magnetic proximity effect between a thin CoO shell (with low N\'eel temperature, TN; and high anisotropy, KAFM) surrounding the Co nanoparticles and the NiO matrix (with high TN but low KAFM). This proximity effect yields an effective AFM with an apparent TN beyond that of bulk CoO, and an enhanced anisotropy compared to NiO. In turn, the Co core FM moment is stabilized against thermal fluctuations via core-shell exchange-bias coupling, leading to the observed TB increase. Mean-field calculations provide a semi-quantitative understanding of this magnetic- proximity stabilization mechanism

Single cell gel electrophoresis as a tool to assess genetic damage in Heleobia cf. australis (Mollusca: Gastropoda) as sentinel for industrial and domestic pollution in Montevideo bay (Uruguay)

O conhecimento dos danos no DNA em organismos aquáticos de áreas poluídas é uma questão importante, já que a contaminação pode vir a alterar os organismos em níveis subletais. Apesar dos moluscos terem sido amplamente utilizados para monitorar a poluição da água, não há registros de estudos in vivo de genotoxicidade. Heleobia cf. australis é um pequeno gastrópode amplamente distribuído em quase todos os ecossistemas costeiros uruguaios, inclusive em locais altamente poluídos. O ensaio do cometa é um biomarcador genético do dano baseado na migração de fragmentos de DNA com carga negativa produzidas por agentes mutagênicos. Foram coletados indivíduos vivos na Baía de Montevidéu (área impactada) e Laguna Garzón (área controle) para analisar a presença de agentes mutagênicos que ocasionassem dano genético. Células de organismos da área impactada apresentaram níveis significativamente mais elevados de danos genéticos do que os obtidos na área controle. Esse nível de dano foi medido pela porcentagem de DNA na cauda. Embora preliminar, esta abordagem apoia a noção de que H. cf. australispoderia ser usado como sentinela para avaliar a presença de agentes mutagênicos em ambientes estuarinos, alertando sobre o impacto da poluição em estágios iniciais.The knowledge of the extent of DNA damage in aquatic organisms in polluted areas is an important issue because contamination may alter their health at sublethal levels. Although molluscs have been widely used to monitor water pollution, there are no records of in vivo genotoxicity studies. Heleobia cf. australis, is distributed in almost all Uruguayan coastal ecosystems, including highly polluted sites. The comet assay is a damage genetic biomarker based on the migration of negatively charged DNA fragments produced by mutagenic agents in individual cells. Live individuals were collected in the Montevideo Bay (impacted area) and Laguna Garzón (control) to analyze the presence of mutagenic agents in the former site through comet assay. Cells from organisms of the impacted area showed significantly higher levels of genetic damage than those obtained in the control population, measured by percentage of DNA in the tail. Although preliminary, this approach supports the idea that H. cf. australis could be used as a sentinel to evaluate the presence of mutagenic agents in estuarine environments, alerting to the impact of contamination in its early stages

Weather, Hydrological and Oceanographic Conditions of the Northern Coast of the Río de la Plata Estuary during ENSO 2009–2010

Climatic, hydrological, and oceanographic conditions were determined during the 2009–2010 El Nino/Southern Oscillation (ENSO) on the north coast of the Río de la Plata (RdlP) estuary. The maximum monthly rainfall was observed in the middle and upper La Plata basin during September 2009 and February 2010 (“El Niño” phase, (EN)). The monthly flow of RdlP showed an increase with rainfall and significant differences between ENSO phases. The wind stress showed fluctuations in both phases, being less intense during EN, during which time maximum flow of RdlP was observed. During the EN phase, increased precipitation contributed to variations in salinity and absence of water column stratification in the north coast of RdlP. This was also associated with variations in Secchi depth, oxygen saturation, and nutrient concentrations. The spatial location of the turbidity front was associated with the flow of the RdlP and wind stress, thus conditioning the physicochemical characteristics of the water column, mainly during EN phase

Performance comparison of biotic indices measuring the ecological status base on soft-bottom macroinvertebrates: a study along the shallow Gomishan lagoon (Southeast Caspian Sea)

This paper aims to test the suitability of some biotic indices for their application in Southeast Caspian Sea. For this purpose, the ecological quality of the Gomishan lagoon was assessed using three biotic indices (AMBI, BENTIX, BOPA) during summer and autumn 2010. The results from the application of the biotic indices do not highlight a clear distinction between the stations. The results show that two of the indices (AMBI and BENTIX) are very close in terms of diagnosis (good and high) and seem to generally perform better than BOPA. In addition, Principal Component Analysis (PCA) based on abiotic parameters showed clear spatial and temporal differences in environmental variables. However, at this shallow sites with low human pressure and high water residence times, such benthic community composition can be associated with physical stress due to salinity increase and to changes in environmental characteristics, triggered by conventional seasonal variations. Natural variability of transitional waters is a crucial factor for a correct evaluation of the ecological condition of macroinvertebrate communities across the lagoonal system.O presente trabalho objetiva testar a viabilidade do emprego de alguns indices bióticos para o Mar Caspio Sudeste. Para tanto, a qualidade ecológica da lagoa Gomishan foi utilizada para avaliar três indices bióticos (AMBI, BENTIX, BOPA) durante o verão e o outono de 2010. Os resultados da aplicação dos indices não permitiram uma distinção clara entre as estações de coleta. Dois dos indices (AMBI e BENTIX) são bastante próximos em termos de diagnose (bom ou alto) e parecem funcionar melhor do que o BOPA. Adicionalmente, a Análise em Componentes Principais (ACP), baseada em parâmetros abióticos, mostrou claras diferenças espaciais e temporais nas variáveis ambientais. Contudo, nesses locais rasos e sem pressão do homem e com alto tempo de residência da água, a composição da comunidade bêntica pode ser associada ao estressse físico, devido ao aumento de salinidade e mudanças nas características ambientais, aliado a mudanças sazonais convencionais. A variabilidade natural de águas de transição mostrou ser um fator crucial para a correta avaliação da condição ecológica das comunidades de macroinvertebrados ao longo do sistema lagunar

Benthic macrofauna structure in the northeast area of Todos os Santos Bay, Bahia State, Brazil: patterns of spatial and seasonal distribution

A estrutura da macrofauna bêntica das regiões entre marés e infralitoral raso na porção nordeste da Baia de Todos os Santos (BTS), nordeste do Brasil, foi investigada durante um período de dois anos. Sua relação com os parâmetros ambientais mensurados foi estudada através de análises estatísticas uni -e multivariadas, sendo os principais padrões de distribuição espacial e temporal relacionados principalmente ao tipo de sedimento e ao conteúdo de três indicadores da matéria orgânica sedimentar (Carbono, Nitrogênio e Fósforo). A macrofauna, composta majoritariamente por anelídeos poliqueta (cerca de 70% do total), apresentou baixa densidade, riqueza de espécies e diversidade, exceto nas estações amostradas nos bancos recifais. Estes se destacam como ambiente peculiar, formado por sedimentos grosseiros, pobres em matéria orgânica e ricos em carbonatos, apresentando fauna abundante e diversificada. A região entre marés e os locais rasos adjacentes à refinaria RLAM são formados por sedimentos compostos principalmente por areia fina e baixo conteúdo orgânico e constituem ambiente instável, com poucas espécies altamente dominantes, como Armandia polyophthalma e Laeonereis acuta. Em outras regiões da BTS, onde dominam os sedimentos pelíticos, densidade e diversidade foram muito baixas, especialmente nas proximidades da refinaria. Aqui, os indicadores biológicos apresentaram seus mais baixos valores, sendo as estações mais próximas (4 e 7) algumas vezes azóicas. A região adjacente de Caboto, inicialmente considerada como controle, apresentou baixa densidade, porém valores médios para diversidade, o que indica ser este ambiente relativamente menos perturbado. Foi possível identificar a existência de 5 grupos com padrões estruturais próprios (entremarés; bancos recifais; infralittoral pelitico; sedimentos mistos; Caboto), que parecem estar relacionados principalmente às características físicas e químicas do sedimento.Structure of intertidal and subtidal benthic macrofauna in the northeastern region of Todos os Santos Bay (TSB), northeast Brazil, was investigated during a period of two years. Relationships with environmental parameters were studied through uni-and multivariate statistical analyses, and the main distributional patterns shown to be especially related to sediment type and content of organic fractions (Carbon, Nitrogen, Phosphorus), on both temporal and spatial scales. Polychaete annelids accounted for more than 70% of the total fauna and showed low densities, species richness and diversity, except for the area situated on the reef banks. These banks constitute a peculiar environment in relation to the rest of the region by having coarse sediments poor in organic matter and rich in biodetritic carbonates besides an abundant and diverse fauna. The intertidal region and the shallower area nearer to the oil refinery RLAM, with sediments composed mainly of fine sand, seem to constitute an unstable system with few highly dominant species, such as Armandia polyophthalma and Laeonereis acuta. In the other regions of TSB, where muddy bottoms predominated, densities and diversity were low, especially in the stations near the refinery. Here the lowest values of the biological indicators occurred together with the highest organic compound content. In addition, the nearest sites (stations 4 and 7) were sometimes azoic. The adjacent Caboto, considered as a control area at first, presented low density but intermediate values of species diversity, which indicates a less disturbed environment in relation to the pelitic infralittoral in front of the refinery. The results of the ordination analyses evidenced five homogeneous groups of stations (intertidal; reef banks; pelitic infralittoral; mixed sediments; Caboto) with different specific patterns, a fact which seems to be mainly related to granulometry and chemical sediment characteristics

Inventory of the marine soft bottom macrofauna of São Sebastião Channel, southeastern Brazilian continental shelf

Analysis of macrofauna from 91 quantitative soft-bottom samples (from five surveys) obtained in the São Sebastião Channel at depths ranging from 2 to 45 m yielded 431 species from a total of 38,630 individuals. The present contribution gives a list of the species found in the area and their depth distribution and sedimentary preferences (granulometric characteristics of the sites where they occurred). This is the first complete inventory of the subtidal invertebrate soft-bottom fauna of the São Sebastião Channel, a peculiar marine area under crescent human impact.