Diluted manganese on the bond-centered site in germanium

The functional properties of Mn-doped Ge depend to large extent on the lattice location of the Mn impurities. Here, we present a lattice location study of implanted diluted Mn by means of electron emission channeling. Surprisingly, in addition to the expected substitutional lattice position, a large fraction of the Mn impurities occupies the bond-centered site. Corroborated by ab initio calculations, the bond-centered Mn is related to Mn-vacancy complexes. These unexpected results call for a reassessment of the theoretical studies on the electrical and magnetic behavior of Mn-doped Ge, hereby including the possible role of Mn-vacancy complexes

Local Polynomial Estimation for Sensitivity Analysis on Models With Correlated Inputs

Sensitivity indices when the inputs of a model are not independent are estimated by local polynomial techniques. Two original estimators based on local polynomial smoothers are proposed. Both have good theoretical properties which are exhibited and also illustrated through analytical examples. They are used to carry out a sensitivity analysis on a real case of a kinetic model with correlated parameters.Comment: 12 page

Stressed, but not defenceless: no obvious influence of irradiation levels on antifeeding and antifouling defences of tropical macroalgae

The production of defence metabolites is assumed to be costly in metabolic terms. If this holds true, low-light stress should reduce the ability of seaweeds to defend themselves chemically against herbivory and fouling. We investigated the effect of energy limitation on the defensive status of seaweeds by assessing their attractiveness to mesograzers and their activity against a bivalve macrofouler in comparison with non-stressed conspecifics. The macroalgae Codium decorticatum (Woodw.) M. Howe, Osmundaria obtusiloba (C. Agardh) R. E. Norris, Pterocladiella capillacea (S. G. Gmel.) Santel. and Hommer., Sargassum vulgare C. Agardh and Stypopodium zonale (Lamour.) Papenf. collected at the southeastern Brazilian coast were exposed to six levels of irradiation (between 1 and 180 μmol photons m−2 s−1) for 10–14 days. After this period, algae from all treatment levels were: (a) processed as artificial food and offered to an amphipod community dominated by Elasmopus brasiliensis Dana and (b) extracted to test for differences in settlement rates of the fouling mussel Perna perna L. on filter paper loaded with the crude extracts. Generally, photosynthesis rates and growth were reduced under low light conditions. Attractiveness to herbivores and macrofoulers, however, was insensitive to energy limitation. We discuss possible explanations for the observed absence of a relationship between light availability and algal defence including the change in nutritional value of the algal tissue, the allocation of resources towards defence instead of growth and the absence of costs for defence

Effect of mesograzer and nutrient levels on the induction of defenses in several Brazilian acroalgae

Herbivory can greatly modify benthic community structure by affecting the distribution of algal species. To deter herbivores, algae have developed several mechanisms, including the induction of chemical and morphological defenses, which may be influenced by nutrient availability. We tested 4 red (Chondrophycus flagellifera, Cryptonemia seminervis, Osmundaria obtusiloba, Pterocladiella capillacea), 4 brown (Dictyota menstrualis, Lobophora variegata, Sargassum vulgare, Stypopodium zonale), and 1 green (Codium decorticatum) algae for inducible defenses following exposure to direct consumption by an amphipod community dominated by Elasmopus brasiliensis. In addition, the effects of water-borne cues from nearby grazed conspecifics and non-grazing consumers on the induction of defenses were examined in C. decorticatum under natural and enhanced (200% natural) nutrient levels. Induction of defense was assessed in choice-feeding assays, using live algae or artificial food containing non-polar extracts of amphipod-exposed (treated) and non-exposed (control) algae. Palatability levels, estimated as the relative difference in wet mass due to consumption in feeding assays between grazer-exposed and control plants, declined significantly in 3 species after the acclimatization period. Tissue from the directly consumed red alga P. capillacea (live alga) was significantly less palatable than tissue from the control plants. Likewise, a significant effect was observed in the brown alga L. variegata. Similar, although not statistically significant, trends were observed in 6 other species. For the green alga C. decorticatum, nutrient enrichment did not affect induction of defenses by herbivores, yet unfertilized plants were more palatable than fertilized conspecifics

Role of magnetic anisotropy on the magnetic properties of Ni nanoclusters embedded in a ZnO matrix

We have investigated the magnetic properties of Ni nanoaggregates produced by ion implantation in ZnO single crystals. Several deviations from classical models usually adopted to describe the magnetic properties of nanoparticle systems were found. The strain between host and Ni nanoaggregates induces a magnetic anisotropy with a preferred direction. We show that these anisotropy effects can be misinterpreted as a ferromagnetic or antiferromagnetic coupling among the nanoaggregates similar to that of an oriented, interacting nanocrystal ensemble

Investigations of Carbon Nitride-Supported Mn3O4 Oxide Nanoparticles for ORR

Earth-abundant Mn-based oxide nanoparticles are supported on carbon nitride using two different immobilization methods and tested for the oxygen reduction reaction. Compared to the metal free CN, the immobilization of Mn oxide enhances not only the electrocatalytic activity but also the selectivity towards the 4e- reduction reaction of O-2 to H2O. The XPS analysis reveals the interaction of the pyridine N species with Mn3O4 nanoparticles being particularly beneficial. This interaction is realized-although to a limited extent-when preparing the catalysts via impregnation; via the oleic acid route it is not observed. Whilst this work shows the potential of these systems to catalyze the ORR, the main limiting factor is still the poor conductivity of the support which leads to overpotential

Methyl Ester Functionalized Phenalenyl Arene- and Bipyridine-Ruthenium-Based Complexes for Electroactive Langmuir-Blodgett Films

We report the synthesis of a new phenalenyl ligand, functionalized with a methyl ester electron withdrawing group, named 9-hydroxy-1-oxo-1H-phenalen-5-methyl carboxylate (L), and the generated complexes [Ru(bpy)2L]PF6 and [(η6-C6H6)Ru(L)Cl]. Compounds were characterized by spectroscopic and X-ray diffraction methods, and their electrochemical behavior was investigated via cyclic voltammetry and UV-vis spectroelectrochemistry. The one-electron oxidized compounds have an unpaired electron located in the phenalenyl ring, as supported by theoretical calculations (DFT) and EPR results. Langmuir-Blodgett (LB) films deposited by [Ru(bpy)2L]2+/3+ species mixed with stearic acid are electroactive, showing a quasi-reversible wave with E1/2Film1 = 0.74 V and E1/2Film2 = 0.81, which are promising systems that allow access to immobilized open-shell species in the film

Re-structuring of marine communities exposed to environmental change

Species richness is the most commonly used but controversial biodiversity metric in studies on aspects of community stability such as structural composition or productivity. The apparent ambiguity of theoretical and experimental findings may in part be due to experimental shortcomings and/or heterogeneity of scales and methods in earlier studies. This has led to an urgent call for improved and more realistic experiments. In a series of experiments replicated at a global scale we translocated several hundred marine hard bottom communities to new environments simulating a rapid but moderate environmental change. Subsequently, we measured their rate of compositional change (re-structuring) which in the great majority of cases represented a compositional convergence towards local communities. Re-structuring is driven by mortality of community components (original species) and establishment of new species in the changed environmental context. The rate of this re-structuring was then related to various system properties. We show that availability of free substratum relates negatively while taxon richness relates positively to structural persistence (i.e., no or slow re-structuring). Thus, when faced with environmental change, taxon-rich communities retain their original composition longer than taxon-poor communities. The effect of taxon richness, however, interacts with another aspect of diversity, functional richness. Indeed, taxon richness relates positively to persistence in functionally depauperate communities, but not in functionally diverse communities. The interaction between taxonomic and functional diversity with regard to the behaviour of communities exposed to environmental stress may help understand some of the seemingly contrasting findings of past research

3D Lowest Landau Level Theory Applied to YBCO Magnetization and Specific Heat Data: Implications for the Critical Behavior in the H-T Plane

We study the applicability of magnetization and specific heat equations derived from a lowest-Landau-level (LLL) calculation, to the high-temperature superconducting (HTSC) materials of the YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) family. We find that significant information about these materials can be obtained from this analysis, even though the three-dimensional LLL functions are not quite as successful in describing them as the corresponding two-dimensional functions are in describing data for the more anisotropic HTSC Bi- and Tl-based materials. The results discussed include scaling fits, an alternative explanation for data claimed as evidence for a second order flux lattice melting transition, and reasons why 3DXY scaling may have less significance than previously believed. We also demonstrate how 3DXY scaling does not describe the specific heat data of YBCO samples in the critical region. Throughout the paper, the importance of checking the actual scaling functions, not merely scaling behavior, is stressed.Comment: RevTeX; 10 double-columned pages with 7 figures embedded. (A total of 10 postscript files for the figures.) Submitted to Physical Review