Review and comparison of effective delayed neutron fraction calculation methods with Monte Carlo codes

The calculation of the effective delayed neutron fraction, beff , with Monte Carlo codes is a complex task due to the requirement of properly considering the adjoint weighting of delayed neutrons. Nevertheless, several techniques have been proposed to circumvent this difficulty and obtain accurate Monte Carlo results for beff without the need of explicitly determining the adjoint flux. In this paper, we make a review of some of these techniques; namely we have analyzed two variants of what we call the k-eigenvalue technique and other techniques based on different interpretations of the physical meaning of the adjoint weighting. To test the validity of all these techniques we have implemented them with the MCNPX code and we have benchmarked them against a range of critical and subcritical systems for which either experimental or deterministic values of beff are available. Furthermore, several nuclear data libraries have been used in order to assess the impact of the uncertainty in nuclear data in the calculated value of beff

Distribution, Abundance and Molecular Analysis of Genus Barbadocladius Cranston & Krosch (Diptera, Chironomidae) in Tropical, High Altitude Andean Streams and Rivers

The distribution of the genus Barbadocladius Cranston & Krosch (Diptera: Chironomidae), previously reported from Chile to Bolivia, has extended northwards. Larvae, pupae and pupal exuviae of this genus have been found in the high mountain tropical streams of Peru to 9°22′56″, but are restricted to very high altitude streams (altitudes over 3,278 m asl) compared to the lower altitude streams (below 1,100 m asl) in which the genus is reported in Chile and Argentina. Based on morphological studies, both described species in the genus, Barbadocladius andinus Cranston & Krosch and Barbadocladius limay Cranston & Krosch, have been found in Peru as pupae or pupal exuviae. Morphological analysis of the larvae and pupae revealed no differences between the two described species from Patagonia and Peru, which are of similar size and with a similar armament of hooklets and spines in pupal tergites and sternites. However, molecular analysis of larvae and pupae revealed that in Peru, there are at least two different evolutionary lines, one distributed widely and another restricted to one site. Phylogenetic analysis (using cox1 mitochondrial sequences) of all available sequences of Barbadocladius shows that the Chilean and Argentinean material differs from that of Peru. Therefore, a total of four molecular segregates are identified, although morphologically, neither larvae nor the pupae may be differentiated

Population density and feeding habits of Oreaster reticulatus (Linnaeus, 1758) (Echinodermata, Asteroidea) living in seagrass beds off Venezuela

We determined the density and size ranges of individuals of the asteroid Oreaster reticulatus (Linnaeus, 1758) from three populations off the Venezuelan coast. Individuals were collected by hand, visually inspecting 100 m² quadrates in the localities of Caño León (N = 10), Las Luisas (N = 24), and Mochima (N = 5). In the field, each individual was turned upside down, in order to determine the condition of the asteroid's stomach (everted vs retracted), and to describe the substrate to which they were associated. Individuals were preserved and their gut contents were analyzed in the laboratory. Oreaster reticulatus (L., 1758) was found 65 % of the times on silt and in areas with low seagrass densities. At Las Luisas, the density of the asteroid was 0.0075 indiv/ m². However, in Caño León and Mochima, densities were at least one or two orders of magnitude higher, reaching 0.072 indiv/m² and 0.2 indiv/m², respectively. Size ranged between 4 and 9.3 cm at Las Luisas; 7.8 and 12.6 cm at Caño León; and 8.5 and 16.5 cm at Mochima. Of the 55 asteroids studied in Caño León, 63.64 % had the stomach everted on the silty substrate. Of these, 14.28 % were feeding on a colonial tunicate, and 71.34 %, on a filamentous alga. Spines of sea urchins were found in 19.05 % of all the specimens collected in Mochima. Previous observations, from laboratory experiments, have shown individuals of Oreaster reticulatus actively predating upon individuals of Lytechinus variegatus (Lamarck, 1818).Con la finalidad de determinar la densidad y talla del asteroideo Oreaster reticulatus (Linnaeus, 1758) presente en tres localidades de fanerógamas de Venezuela, se realizaron cuadrículas de 100 m² en las estaciones de Caño León (10), Las Luisas (24) y Mochima (5). La dieta de O. reticulatus (L., 1758) se determinó levantando cada uno de los ejemplares conseguidos y observando si el estómago se encontraba evertido y la naturaleza del sustrato. El asteroideo se encontró un 65 % de las veces sobre sedimento o en áreas de poca vegetación. La densidad en la localidad de Las Luisas fue de 0,0075 indiv/m², siendo un orden de magnitud mayor en Caño León (0,072 indiv/m²), mientras que Mochima presentó las mayores densidades (0,2 indiv/m²). De las 55 estrellas estudiadas en Caño León, un 63,64 % tenía el estómago evertido sobre el sedimento, mientras que un 12,73 % lo tenía sobre las hojas de las fanerógamas. En Mochima, un 14,28 % de los ejemplares se alimentaba de sedimento, un 14,28 % lo hacía sobre un tunicado colonial y un 71,34 % estaba sobre algas filamentosas. Del total observado en Mochima un 19,05 % presentaba espinas de erizos envueltas en el estómago. En laboratorio se realizaron experiencias de depredación sobre el erizo Lytechinus variegatus (Lamarck, 1818), comprobándose depredación activa sobre el mismo, en un periodo aproximado de 6 horas. La talla (radio mayor) de O. reticulatus osciló entre 4 y 9,3 cm en Las Luisas, entre 7,8 y 12,6 cm en Caño León y entre 8,5 y 16,5 cm en Mochima.Instituto Español de Oceanografí

Body size is more important than diet in determining stable-isotope estimates of trophic position in crocodilians

The trophic position of a top predator, synonymous with food-chain length, is one of the most fundamental attributes of ecosystems. Stable isotope ratios of nitrogen (δ 15N) have been used to estimate trophic position of organisms due to the predictable enrichment of 15N in consumer tissues relative to their diet. Previous studies in crocodilians have found upward ontogenetic shifts in their 'trophic position'. However, such increases are not expected from what is known about crocodilian diets because ontogenetic shifts in diet relate to taxonomic categories of prey rather than shifts to prey from higher trophic levels. When we analysed dietary information from the literature on the four Amazonian crocodilians, ontogenetic shifts in dietary-based trophic position (TPdiet) were minimal, and differed from those estimated using δ 15N data (TPSIA). Thus, ontogenetic shifts in TPSIA may result not only from dietary assimilation but also from trophic discrimination factors (TDF or Δ 15N) associated with body size. Using a unique TDF value to estimate trophic position of crocodilians of all sizes might obscure conclusions about ontogenetic shifts in trophic position. Our findings may change the way that researchers estimate trophic position of organisms that show orders of magnitude differences in size across their life span. © 2018 The Author(s)

Biodegradable PEG–dendritic block copolymers: synthesis and biofunctionality assessment as vectors of siRNA

One important drawback of most of the currently used dendrimers for biomedical applications is their high stability under physiological conditions that can result in cytotoxicity or complications induced by the accumulation of non-degradable synthetic materials in the organism. Particularly in the gene therapy field, vector stability can further hinder the intracellular release of the nucleic acid from the dendriplex, consequently leading to low transfection efficiencies. Therefore, biodegradable cationic dendritic structures have been eagerly awaited. However, the development of these dendritic nanocarriers is challenging because of the undesired and/or premature degradation observed during their synthesis and/or application. Here, we report new hybrid-biodegradable, biocompatible, non-toxic, and water-soluble azide-terminated PEG–GATGE dendritic block copolymers, based on a gallic acid (GA) core and triethylene glycol (TG) butanoate arms, incorporating ester bonds (E) at the dendritic arms/shell. Their successful functionalization by “click” chemistry with unprotected alkynated amines allowed complexation and delivery of siRNA. The hydrophobic character of the GATGE building unit confers to these hydrolyzable dendritic bionanomaterials a great ability to complex, protect and mediate the cellular internalization of siRNA. Moreover, the localization of the degradation points at the dendritic periphery, close to the complexed siRNA, was found to be important for nucleic acid release from the nanoparticles, rendering a significant improvement of the transfection efficiency compared to their hydrolytically stable PEG–GATG copolymer counterparts. The present study puts forward these biodegradable PEG–dendritic block copolymers not only as suitable vectors for nucleic acids, but also as new avenues for further developments exploring their use in theranosticsThe authors would like to acknowledge the FEDER funds through the Programa Operacional Factores de Competitividade – COMPETE and the Portuguese funds through FCT – Fundação para a Ciência e a Tecnologia (PTDC/CTM-NAN/112428/2009 and PTDC/CTM-NAN/3547/2014) that supported this work and the FCT / MEC through National Funds and, when applicable, co-financed by the FEDER via the PT2020 Partnership Agreement under the 4293 Unit I&D. V. Leiro acknowledges the support by FCT (SFRH/BPD/69110/2010) and by the project NORTE-01-0145-FEDER-000012, financed by Norte Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). P.M.D. Moreno acknowledges the support from the Marie Curie Actions of the European Community’s Seventh Framework Program (PIEF-GA-2011-300485) and FCT fellowship (SFRH/BPD/108738/2015). This work was also financially supported by the Spanish Government (MINECO: CTQ2012-34790, CTQ2012-33436) and the Xunta de Galicia (CN2011/037)S

Estudio de crecimiento y producción de toxinas en tres especies de Alexandrium: A. catenella, A. peruvianum y A. ostenfeldii.

Se estudió el crecimiento y el contenido en toxinas de 3 especies de dinoflagelados: Alexandrium catenella, A. peruvianum y A. ostenfeldii. A. catenella mostró tasas de crecimiento más elevadas que las otras dos especies. Las tres especies crecieron más rápidamente a 26ºC y menos a 15ºC aunque las tasas de crecimiento no mostraron grandes diferencias. Se observaron diferentes ventanas óptimas de crecimiento en relación a la salinidad en las tres especies. Las máximas tasas de crecimiento fueron a 32 y 37 de salinidad para A. catenella, a 25 de salinidad para A. peruvianum y a 10 de salinidad para A. ostenfeldii. Las tres especies produjeron toxinas PSP pero en muy diferentes cantidades, mostrando notables diferencias en el perfil de toxinas: (10 componentes A. catenella: C1, C2, GTX1-6, neoSTX y STX; 3 componentes A ostenfeldii y A. peruvianum: GTX2-3 y STX). La concentración de toxinas PSP en A. peruvianum fue muy baja. Se detectó también presencia de espirólidos (13-Desmetil-SPX C) en A. peruvianum y Gymnodimina-A en A. ostenfeldii

New national and regional bryophyte records, 72

ABSTRACT: New record of Sphagnum palustre L. to Graciosa Island (Azores).info:eu-repo/semantics/publishedVersio