Stabilized jellium model and structural relaxation effects on the fragmentation energies of ionized silver clusters

Using the stabilized jellium model in two schemes of `relaxed' and `rigid', we have calculated the dissociation energies and the fission barrier heights for the binary fragmentations of singly-ionized and doubly-ionized Ag clusters. In the calculations, we have assumed spherical geometries for the clusters. Comparison of the fragmentation energies in the two schemes show differences which are significant in some cases. This result reveals the advantages of the relaxed SJM over the rigid SJM in dynamical processes such as fragmentation. Comparing the relaxed SJM results and axperimental data on fragmentation energies, it is possible to predict the sizes of the clusters just before their fragmentations.Comment: 9 pages, 12 JPG figure

Effect of particle size distribution and dynamics on the performance of two-dimensional packing

AbstractExtensive computer simulation is used to revisit and to generalize two classical problems: (i) the random car-parking dynamics of A. Rényi and (ii) the irreversible random sequential adsorption (RSA) of parallel squares of same size on a planar substrate of area L2. In this paper, differently from the classical RSA, the squares obey the size distribution n(a)=n(1)a−τ, where a=1,2,3,… is the area of the squares. Using this scaling distribution and three classes of packing dynamics we study the final packing fraction of particles, ⊖(τ,L), and in particular its thermodynamic limit L→∞. We show that the efficiency to attain a high/low packing density of particles on the substrate is strongly dependent on the value of the exponent τ and on the characteristics of the dynamics

Friedel oscillations in one-dimensional metals: from Luttinger's theorem to the Luttinger liquid

Charge density and magnetization density profiles of one-dimensional metals are investigated by two complementary many-body methods: numerically exact (Lanczos) diagonalization, and the Bethe-Ansatz local-density approximation with and without a simple self-interaction correction. Depending on the magnetization of the system, local approximations reproduce different Fourier components of the exact Friedel oscillations.Comment: 3 pages, 3 figures, Manuscript accepted by Journal of Magnetism and Magnetic Materials, special issue for LAWMMM 2007 conferenc

Dry matter and area partitioning, radiation interception and radiation-use efficiency in open-field bell pepper

The objective of this study was to determine some key components of a model for bell pepper growth and yield under non-limiting water and nutrient conditions using data from field trials conducted in Southern Portugal. DM partitioning, at least before fruiting, and specific area indices for leaves, stems and fruits were conservative in relation to normalized thermal time. The interception model had a good performance. It was based on the exponential extinction of radiation on the area covered by the plants, the ellipsoidal leaf-angle distributionmodel (X-parameter 2.48 and 2.89), and absorptivities of the leaves for PAR and NIR, 0.8 and 0.2, respectively. Radiation-use efficiency (RUE) was determined and presented in four different forms. RUE did not change substantially throughout the growing season. RUE of irrigated pepper crops grown in our experiments was around 1.6 g MJ 1 of intercepted PAR. The models and parameter values presented in this study may be useful to simulate the development and growth of fieldgrown pepper cro

Spatial diet overlap and food resource in two congeneric mullet species revealed by stable isotopes and stomach content analyses

Food partitioning among coexisting species in different habitats remains an important research topic in trophic ecology. In this work, we combined carbon and nitrogen stable isotope ratios and stomach content analyses to investigate differences in diet and niche overlap of two congeneric juvenile mullet species (Mugil curema and Mugil liza) coexisting in a marine surf-zone and an estuarine zone in southern Brazil (29oS). These habitats have contrasting levels of food availability, especially in terms of prey diversity, with higher microalgae diversity in the estuary than in the marine surf-zone. In these contrasting conditions, we predicted that both mullet species will have (a) higher niche overlap and smaller niche breadth at the marine surf-zone due to the common exploration of highly abundant surf-zone diatoms and (b) lower niche overlap and higher niche breadth inside the estuary due to selective feeding on more diverse food resources. Isotope niche areas (measured as standard ellipse areas) were higher in the estuary (6.10 and 6.18) than in the marine surf-zone (3.68 and 3.37) for both M. curema and M. liza, respectively. We observed an overlap of 52% in isotopic niches of both species in the marine surf-zone and none in the estuary. We also found contrasting patterns in the diet composition between species according to the habitat. At the marine surfzone, diatoms of the classes Bacillariophyceae and Coscinodiscophyceae dominated (> 99%) the food content of both mullet species. In contrast, green algae, cyanobacteria, dinoflagellates and flagellates comprised the diet of both species in the estuary. These results could be explained by spatial differences in food availability (especially regarding diversity of microalgae) between both habitats. At the marine site, both species explored the most abundant microalgae available (mostly the surf-zone diatom Asterionellopsis cf. guyunusae and fragments of Coscinodiscus), whereas in the estuary both species shifted their diets to explore the greater diversity of microalgae resources. Overall, our findings revealed that niche partitioning theory could not fully predict changes in breadth and overlap of food niches of estuarine dependent fish species with complex life cycles encompassing marine to estuarine systems with contrasting food availabilities

Harpagifer bispinis

This rocky, intertidal species has a relatively small range, but is common and abundant. There are no known major threats at this time; therefore, it is listed as Least Concern.Fil: Buratti, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Díaz de Astarloa, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Hüne, M.. Universidad Austral de Chile; ChileFil: Irigoyen, A.. No especifíca;Fil: Landaeta, M.. Universidad de Valparaíso; ChileFil: Riestra, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Vieira, J.P.. Universidade Federal Do Rio Grande.; Brasi

The DNA damage response is developmentally regulated in the African trypanosome

Genomes are affected by a wide range of damage, which has resulted in the evolution of a number of widely conserved DNA repair pathways. Most of these repair reactions have been described in the African trypanosome Trypanosoma brucei, which is a genetically tractable eukaryotic microbe and important human and animal parasite, but little work has considered how the DNA damage response operates throughout the T. brucei life cycle. Using quantitative PCR we have assessed damage induction and repair in both the nuclear and mitochondrial genomes of the parasite. We show differing kinetics of repair for three forms of DNA damage, and dramatic differences in repair between replicative life cycle forms found in the testse fly midgut and the mammal. We find that mammal-infective T. brucei cells repair oxidative and crosslink-induced DNA damage more efficiently than tsetse-infective cells and, moreover, very distinct patterns of induction and repair of DNA alkylating damage in the two life cycle forms. We also reveal robust repair of DNA lesions in the highly unusual T. brucei mitochondrial genome (the kinetoplast). By examining mutants we show that nuclear alkylation damage is repaired by the concerted action of two repair pathways, and that Rad51 acts in kinetoplast repair. Finally, we correlate repair with cell cycle arrest and cell growth, revealing that induced DNA damage has strikingly differing effects on the two life cycle stages, with distinct timing of alkylation-induced cell cycle arrest and higher levels of damage induced death in mammal-infective cells. Our data reveal that T. brucei regulates the DNA damage response during its life cycle, a capacity that may be shared by many microbial pathogens that exist in variant environments during growth and transmission

Patagonotothen tessellata

This demersal species inhabits nearshore rocky reefs and kelp forests in southern Chile and Argentina and has an estimated generation length of 5 years. The global-level center of its abundance is in the straits of southern Chile. Invasive Chinook salmon now occur throughout the straits of Chile, and this represents a potential major threat, including impacts from competition, predation and disease introduction. The invasion is expected to expand into other parts of its range (i.e. Argentina). The Chilean salmon aquaculture industry, which is the source of escaped individuals, is expected to expand in the near future. The centre, or the major proportion of its global population is concentrated in the area where this threat is greatest. This threat has been increasing over time, but probably began about 30 years ago. There are no data to quantify population trends at this time; and considering this major threat and the lack of understanding for the likely direct impact, it is listed as Data Deficient. It is highly recommended to conduct studies on population trends as well as the impacts from the invasive salmon. Recommended conservation actions include the continued protection of kelp forests from harvest and to improve management of invasive salmon and prevention of escapes.Fil: Hüne, M.. Universidad Austral de Chile; ChileFil: Díaz de Astarloa, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Landaeta, M.. Universidad de Valparaíso; ChileFil: Buratti, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Irigoyen, A.. No especifíca;Fil: Riestra, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Vieira, J.P.. Universidade Federal Do Rio Grande.; Brasi

Champsocephalus esox, Pike Icefish

This demersal species is endemic to the southern Patagonia Sea region where it occurs in kelp forests and fjords. Its physiology restricts it to waters of high oxygen concentration and low temperature, and its survivability is reduced when these conditions fluctuate. Based on survey data and observations of fishers catch, this species has declined by 80% since the 1980s in at least half of its range (the Chilean coast). The status of its population in the other half of its range (Argentina) is poorly understood due to the lack of surveys. Considering the uncertainty regarding its status in the other half of its range, it is conservatively suspected to have declined overall by 30% over the past three generation lengths (12-18 years). Threats include climate change (warming water temperatures), mortality as bycatch in artisanal fisheries and invasive salmon. It is listed as Vulnerable A2bcde. Additional survey work is needed to monitor and understand its population throughout its range. Research is needed on its life history and response to heat shock.Fil: Buratti, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Díaz de Astarloa, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Hüne, M.. Universidad Austral de Chile; ChileFil: Irigoyen, A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: Landaeta, M.. Universidad de Valparaíso; ChileFil: Riestra, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Vieira, J.P.. Universidade Federal Do Rio Grande.; Brasi

Engraulis anchoita

This coastal to mid-continental shelf, pelagic species is widely distributed from Brazil to Argentina. It is a short-lived species with an estimated generation length of 2-4 years. Biomass fluctuates naturally with environmental conditions. It is currently commercially exploited only in Argentina. The global population is comprised of three stocks (1. southeast Brazil north of 28°S, 2. Brazil south of 28°S, Uruguay and Argentina to 41°S and 3. Argentine Patagonia between 41°S and 48°S). Abundance of the species in Brazil is stable. According to fishery independent scientific surveys, the Buenos Aires stock has a high biomass close to historical levels and it is underexploited. The Argentine population is regularly monitored and there are stringent fishing regulations in place. Fishing activity is not expected to be driving global-level declines approaching a Near Threatened or threatened level at this time. It is listed as Least Concern with a recommendation to continue to conduct research cruises to improve stock assessments. Research is also needed to better understand the observed changes in body size structure of the southern stocks.Fil: Buratti, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Díaz de Astarloa, Juan Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Hüne, M.. Universidad Austral de Chile; ChileFil: Irigoyen, A.. No especifíca;Fil: Landaeta, M.. Universidad de Valparaíso; ChileFil: Riestra, C.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Vieira, J.P.. Universidade Federal Do Rio Grande.; BrasilFil: Di Dario F.. Universidade Federal do Rio de Janeiro; Brasi