Abstract
We investigate three fundamental issues in the physics of high-Tc cuprates, from the perspective of a recently proposed comprehensive theory for these materials. (a) Orbital ordering × ...superconductivity. The first issue is the detailed microscopic mechanism that produces an attractive interaction between holes in high-Tc cuprates. (b) Dispersion relation × pseudogap order parameter. The second issue refers to the existence of a pseudogap order parameter, which would be different from zero all over the pseudogap phase and would vanish elsewhere. (c) Chemical potential × quantum critical point location. The third issue concerns the debate as to whether the quantum critical point, located where the pseudogap transition line
T
*(
x
) meets the
T
= 0 axis is inside the superconducting dome or at its boundary. We obtain clearcut solutions for the three issues.
•AA2198-T851 is a potential substitute for AA2524-T3 with higher pitting resistance.•AA7081-T73511 is more prone to pitting corrosion than the AA7050-T7451.•Cathodic Al7Cu2Fe particles promote ...dissolution of adjacent 7XXX matrix.
The 2XXX and 7XXX series aluminium alloys are commonly used in aircraft applications where high strength-to-weight ratios are required. The present study aims to compare the corrosion resistance of two novel alloys developed for aircraft industry (AA2198-T851 and 7081-T73511) to that presented by the alternative base alloys (AA2524-T3 and 7050-T7451, respectively). Results indicate that AA2198-T851 may show a superior corrosion performance compared to AA2524-T3, being a potential candidate for its replacement, due to best mechanical properties. In what concerns the 7081-T73511, its resistance to pitting corrosion may be lower than for the base line alloy 7050-T7451.
An innovative concept of activation of electrode materials for Li-ion batteries is proposed through the preparation of carbon-phosphorus (P/C) composites. Carbon-encapsulated phosphorus composites ...can be successfully prepared via a simple route by the vaporization–condensation of red phosphorus onto mesoporous carbon. Surface area measurements and Raman spectroscopy were used for the characterization of the P/C composites, which were then tested as anode materials in Li-ion batteries showing enhanced electrochemical properties. In contrast to what is observed for pure unsupported phosphorus, Li storage in P/C composite occurs through the reversible formation of Li
3P during the discharge process, as clearly evidenced by
in situ XRD, leading to capacities greater than 900
mAh
g
−1 after 20
cycles.
After much debate, there is an emerging consensus that the composition of many ecological communities is determined both by species traits, as proposed by niche theory, as well as by chance events. A ...critical question for ecology is, therefore, which attributes of species predict the dominance of deterministic or stochastic processes. We outline two hypotheses by which organism size could determine which processes structure ecological communities, and we test these hypotheses by comparing the community structure in bromeliad phytotelmata of three groups of organisms (bacteria, zooplankton, and macroinvertebrates) that encompass a 10 000-fold gradient in body size, but live in the same habitat. Bacteria had no habitat associations, as would be expected from trait-neutral stochastic processes, but still showed exclusion among species pairs, as would be expected from niche-based processes. Macroinvertebrates had strong habitat and species associations, indicating niche-based processes. Zooplankton, with body size between bacteria and macroinvertebrates, showed intermediate habitat associations. We concluded that a key niche process, habitat filtering, strengthened with organism size, possibly because larger organisms are both less plastic in their fundamental niches and more able to be selective in dispersal. These results suggest that the relative importance of deterministic and stochastic processes may be predictable from organism size.
Local habitat size has been shown to influence colonization and extinction processes of species in patchy environments. However, species differ in body size, mobility, and trophic level, and may not ...respond in the same way to habitat size. Thus far, we have a limited understanding of how habitat size influences the structure of multitrophic communities and to what extent the effects may be generalizable over a broad geographic range. Here, we used water-filled bromeliads of different sizes as a natural model system to examine the effects of habitat size on the trophic structure of their inhabiting invertebrate communities. We collected composition and biomass data from 651 bromeliad communities from eight sites across Central and South America differing in environmental conditions, species pools, and the presence of large-bodied odonate predators. We found that trophic structure in the communities changed dramatically with changes in habitat (bromeliad) size. Detritivore : resource ratios showed a consistent negative relationship with habitat size across sites. In contrast, changes in predator : detritivore (prey) ratios depended on the presence of odonates as dominant predators in the regional pool. At sites without odonates, predator : detritivore biomass ratios decreased with increasing habitat size. At sites with odonates, we found odonates to be more frequently present in large than in small bromeliads, and predator : detritivore biomass ratios increased with increasing habitat size to the point where some trophic pyramids became inverted. Our results show that the distribution of biomass amongst food-web levels depends strongly on habitat size, largely irrespective of geographic differences in environmental conditions or detritivore species compositions. However, the presence of large-bodied predators in the regional species pool may fundamentally alter this relationship between habitat size and trophic structure. We conclude that taking into account the response and multitrophic effects of dominant, mobile species may be critical when predicting changes in community structure along a habitat-size gradient.
The study describes a stand-alone photovoltaic system in which the storage is realized using electrolytic hydrogen, converted into electricity in fuel cells. The aim of the research is the ...optimization of the sizing of the system elements chain (photovoltaic generator, electrolyzer, tank, fuel cell) with respect to the electric load to fulfil.
A positive annual balance between hydrogen production and consumption must be guaranteed; furthermore, energy production surplus that cannot be stored or converted into hydrogen due to batteries or tanks capacity limits must be avoided.
The energetic analysis and that of hydrogen production and consumption have been carried out on an hourly basis using the HOMER software.
The study shows that, being the load active in the evening and the system disconnected from the grid, excess energy cannot be exploited unless large tanks are used, if high gas pressures are to be avoided. Consequently, the system use in public areas or residential buildings, where visual impact generated by tanks is hardly acceptable and safety rules do not allow high gas pressures, is advisable only in grid-connected configurations. Such problems are by far reduced when a marked self consumption is present.
•Hydrogen might represent the energy vector of the future.•RES can be used as a primary source for the production of electrolytic hydrogen.•Electrolysis of water from RES has only byproducts water and heat.•After electrolysis hydrogen is stored and converted into electricity by fuel cells.•The study refers to a real stand-alone PV system equipped with hydrogen storage.
This work aims to improve the corrosion properties of the 2198-T851 aluminium alloy by coating with a set of niobium oxide thin films, using the reactive sputtering technique. The structural and ...morphological properties of the niobium oxide thin films were characterized by using SEM/EDX, AFM, FTIR and Raman spectroscopy. Global electrochemical tests (OCP, PPc, CV, and EIS) were performed in 0.6 mol L−1 NaCl solution. The results demonstrated that the reactive sputtering technique was advantageous for producing thin films on the 2198-T851 aluminium surface. Raman spectroscopy results revealed a band near 650 cm−1 related to NbO single bonds, whilst the band centred at 868 cm−1 may be attributed to NbO double bonds. The PPc results indicated that the niobium oxide acts as a protective barrier, since a difference of about 210 mV was observed between Epitting and Ecorr. The coated specimens displayed a superior breakdown potential when compared to the base material (−0.387 vs − 0.505 V/SCE). The impedance modulus has increased more than one order of magnitude and the phase angle is closer to - 90°, demonstrating a capacitive thin film was deposited on the 2198-T851 aluminium alloy surface.
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•The reactive sputtering method was able to produce NbxOy film on the 2198-T851.•Coated material has increased the impedance modulus more than one order of magnitude.•A difference of about 210 mV between the corrosion and pitting potentials was obtained..•A higher resistance to localised corrosion was achieved when compared to the untreated alloy.
This book focuses on the mind and its ability to seek answers to unknown or unanswered questions. The theory of educating provides the grounding for using V diagrams by students, educators, ...researchers, and parents. Teachers make lesson plans using V diagrams and concept maps. They become expert coaches in guiding student performances. Students learn to construct their own knowledge. They change from question-answerers to question-askers. Parents share meaning with their children and their children's teachers and administrators. Administrators monitor programs and are in touch with all participants in schools and universities. Researchers and evaluators can share records of events and facts. With this theory working in the classrooms and laboratories of many practical places of educating plus extending into the world of technology literacy, The Art of Educating with V Diagrams explains how educating works.
Recently the renormalization of the band gap m , in both tungsten diselenide ( WSe2) and molybdenumm disulfide ( MoS2 ), has been experimentally measured as a function of the carrier concentration n .... The main result establishes a decreasing of hundreds of meV, in comparison with the bare band gap, as the carrier concentration increases. These materials are known as transition metal dichalcogenides and their low-energy excitations are, approximately, described by the massive Dirac equation. Using pseudo–quantum electrodynamics (PQED) to describe the electromagnetic interaction between these quasiparticles and from renormalization group analysis at the largeN limit, we obtain that the renormalized mass describes the band gap renormalization with a function given by m ( n ) / m0 = ( n / n0 ) Cλ/2, where m0 = m ( n0 ) and Cλ is a function of the coupling constant λ = πα/4, where α is the fine-structure constant. We compare our theoretical results with the experimental findings for WSe2 and MoS2, and we conclude that our approach is in agreement with these experimental results for reasonable values of λ . Thereafter, we consider the coupling of massless Dirac particles with the Gross-Neveu interaction, which generates a mass for the Dirac field through the gap equation, and PQED. In this case, we show that there exists a critical coupling constant, namely, λc ≈ 0 , 66 in which the beta function of the mass vanishes, providing a stable fixed point in the ultraviolet limit. For λ > λc, the renormalized mass decreases while for λ < λc it increases with the carrier concentration.
Climate change and biodiversity loss are expected to simultaneously affect ecosystems, however research on how each driver mediates the effect of the other has been limited in scope. The multiple ...stressor framework emphasizes non-additive effects, but biodiversity may also buffer the effects of climate change, and climate change may alter which mechanisms underlie biodiversity–function relationships. Here, we performed an experiment using tank bromeliad ecosystems to test the various ways that rainfall changes and litter diversity may jointly determine ecological processes. Litter diversity and rainfall changes interactively affected multiple functions, but how depends on the process measured. High litter diversity buffered the effects of altered rainfall on detritivore communities, evidence of insurance against impacts of climate change. Altered rainfall affected the mechanisms by which litter diversity influenced decomposition, reducing the importance of complementary attributes of species (complementarity effects), and resulting in an increasing dependence on the maintenance of specific species (dominance effects). Finally, altered rainfall conditions prevented litter diversity from fueling methanogenesis, because such changes in rainfall reduced microbial activity by 58%. Together, these results demonstrate that the effects of climate change and biodiversity loss on ecosystems cannot be understood in isolation and interactions between these stressors can be multifaceted.
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