Exciton energies and wave functions in hexagonal Boron Nitride using Miller and Good’s uniform approach

In this paper we revisit the work of Miller and Good, which describes an uniform JWKB type of approximation to the solution of quantum problems. This paper, very well known in atomic physics in the 1970's 1980's of the last century, did not attract the same attention from the condensed matter community. Contrary to the usual JWKB approach, Miller and Good's method yields wave functions that do not diverge at the classical turning points. We apply the method in the context of two-dimensional excitons, an important condensed matter system. In particular, we apply our results to excitons in hexagonal boron nitride, solving the corresponding Wannier equation. We compare the semiclassical results with others from the literature and find good agreement.The authors acknowledge Mike Belsley for carefully reading the manuscript and for comments that allowed to improve the overall presentation. N.M.R.P. acknowledges support from the European Commission through the project "Graphene-Driven Revolutions in ICT and Beyond" (Ref. no. 881603 - core 3), and the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Financing UID/FIS/04650/2019. In addition, N.M.R.P. acknowledges COMPETE2020, PORTUGAL2020, FEDER and the Portuguese Foundation for Science and Technology (FCT) through projects POCI-01-0145-FEDER-028114, POCI-01-0145-FEDER- 029265, PTDC/NAN-OPT/29265/2017, and POCI-01-0145-FEDER-02888

Electronic doping of graphene by deposited transition metal atoms

We perform a phenomenological analysis of the problem of the electronic doping of a graphene sheet by deposited transition metal atoms, which aggregate in clusters. The sample is placed in a capacitor device such that the electronic doping of graphene can be varied by the application of a gate voltage and such that transport measurements can be performed via the application of a (much smaller) voltage along the graphene sample, as reported in the work of Pi et al. [Phys. Rev. B 80, 075406 (2009)]. The analysis allows us to explain the thermodynamic properties of the device, such as the level of doping of graphene and the ionisation potential of the metal clusters in terms of the chemical interaction between graphene and the clusters. We are also able, by modelling the metallic clusters as perfect conducting spheres, to determine the scattering potential due to these clusters on the electronic carriers of graphene and hence the contribution of these clusters to the resistivity of the sample. The model presented is able to explain the measurements performed by Pi et al. on Pt-covered graphene samples at the lowest metallic coverages measured and we also present a theoretical argument based on the above model that explains why significant deviations from such a theory are observed at higher levels of coverage.Comment: 16 pages, 10 figure

Unintended multispecies co-benefits of an Amazonian community-based conservation programme

Urgent challenges posed by widespread degradation in tropical ecosystems with poor governance require new development pathways to reconcile biodiversity conservation and human welfare. Community-based conservation management has shown potential for integrating socio-economic needs with conservation goals in tropical environments; however, assessing the effectiveness of this approach is often held back by the lack of comprehensive ecological assessments. We conduct a robust ecological evaluation of the largest community-based conservation management initiative in the Brazilian Amazon over the last 40 years. We show that this programme has induced large-scale population recovery of the target giant South American turtle (Podocnemis expansa) and other freshwater turtles along a 1,500-km section of a major tributary of the Amazon River. Poaching activity on protected beaches was around 2% compared to 99% on unprotected beaches. We also find positive demographic co-benefits across a wide range of non-target vertebrate and invertebrate taxa. As a result, beaches protected by local communities represent islands of high biodiversity, while unprotected beaches remain ‘empty and silent’, showing the effectiveness of empowering local conservation action, particularly in countries experiencing shortages in financial and human resources

Supervised chemical pattern recognition in almond (Prunus dulcis) Portuguese PDO cultivars: a PCA and LDA based triennial study

Almonds harvested in three years in Trás-os-Montes (Portugal) were characterized to find differences among Protected Designation of Origin (PDO) Amêndoa Douro and commercial non-PDO cultivars. Nutritional parameters, fiber (neutral and acid detergent fibers, acid detergent lignin and cellulose), fatty acids, triacylglycerols (TAG) and tocopherols were evaluated. Fat was the major component, followed by carbohydrates, protein and moisture. Fatty acids were mostly detected as monounsaturated and polyunsaturated forms, with relevance of oleic and linoleic acids. Accordingly, 1,2,3-trioleoylglycerol and 1,2-dioleoyl-3-linoleoylglycerol were the major TAG. α-Tocopherol was the leading tocopherol. To verify statistical differences among PDO and non-PDO cultivars independently of the harvesting year, data were analyzed through an analysis of variance, a principal components analysis and a linear discriminant analysis (LDA). These differences identified classification parameters, providing an important tool for authenticity purposes. The best results were achieved with TAG analysis coupled with LDA, that proved its effectiveness to discriminate almond cultivars

Characterization of phenolic compounds of OMW : toxicity and degradability by yeasts

The characterization of Olive Mill Wastewaters (OMW), focusing the phenolic compounds, is one of the aims of the present work. As a first approach to characterize the phenolic compounds of OMW, the extraction methods used were: a liquid-liquid extraction by acidified ethyl acetate and a solid-liquid extraction with acidified methanol. The analysis of these extracts by reversed phase liquid chromatography confirmed that hydroxytyrosol was the most abundant phenolic compound in OMW, and that this compound was more efficiently recovered by the solid-liquid extraction technique. It was also a goal of this work to study the phenolic compounds toxicity to some yeast strains. Among the phenolic compounds tested catechol is the most inhibitory one to the cells. The phenols degradation was quite difficult, particularly when more easily degradable carbon source is still present in the medium.Fundação para a Ciência e a Tecnologia (FCT) - PTDC/AMB/69379/2006, SFRH/BD/27915/200

Chemical characterization of chestnut cultivars from three consecutive years: chemometrics and contribution for authentication

Four Castanea sativa Miller cultivars (Aveleira, Boaventura, Judia and Longal) belonging to the Protected Designation of Origin ‘‘Castanha da Terra Fria’’, from the Northeast of Portugal, were selected in 2006, 2007 and 2008. Their nutritional, fatty acids, triacylglycerols and tocopherols profiles were evaluated. Water was the major component, followed by carbohydrates, protein and fat, with energetic values lower than 190 kcal/100 g of fresh fruit. Oleic, linoleic and palmitic were the major fatty acids, 1-oleoyl-2-linoleoyl- 3-linoleoyl-sn-glycerol, 1-linoleoyl-2-linoleoyl-3-palmitoyl-sn-glycerol, 1-oleoyl-2-linoleoyl-3- oleoyl-sn-glycerol and 1-linoleoyl-2-oleoyl-3-palmitoyl-sn-glycerol were the prevalent triacylglycerols and c-tocopherol was the most abundant tocopherol. In each parameter, differences between cultivars, harvest year and the possible cultivar year interaction were screened through a two-way analysis of variance. Differences among cultivars have been attenuated by the variability among years, leading, in general, to a significant interaction effect, which resulted in a relative homogeneity regarding chemical parameters, showing that nutritional and chemical composition was influenced by seasonal variability. A stepwise linear discriminant model, based on 10 (a-tocopherol, c-tocotrienol, LLL, OLLn, d-tocopherol, c-tocopherol, d-tocotrienol, PLLn, protein and OOO) of the 38 initial evaluated variables was also established. The model allowed the complete discrimination of cultivars with overall sensibilities and specificities of 100%, for both original grouped data and leave-one-out cross-validation procedures. Furthermore, similar results were also obtained using only tocopherols data, showing their usefulness as a discriminant factor for chestnut cultivars

Characterization of phenolic compounds of OMW: toxicity and degrability by yeasts

The olive oil extraction, performed by the 3-phases process, results on a large amount of an effluent, usually known as Olive Mill Wastewater (OMW). It is mainly produced in the Mediterranean area, with the exception of Spain that is one of the major producers but mostly use the 2-phases process. OMW represents a major environmental problem due to its high organic content, being characterized by a strong acidic smell and an intensive brown to dark color due to the presence of biodegradable, recalcitrant and biostatic compounds. OMW phytotoxicity can be attributed to the phenolic compounds (Lanciotti et al, 2005). Owing to their instability, OMW phenols tend to polymerise during storage into condensed high-molecular-weight polymers that are difficult to degrade (Crognale et al, 2006). Thus, uncontrolled OMW disposal can create severe risks to water and soil quality. OMW is currently concentrated by evaporation in open pools, but this method is not satisfactory because a black foul-smelling sludge, difficult to remove, is produced. Instead of disposal solutions an approach of using this waste as a resource to be valorized is of greater interest. In fact, OMW contains sugars, lipids, mineral elements and phenolic compounds (10 % of the organic matter) that could be either directly recovered by chemical extraction and subsequent purification, or utilized as a basis for fermentative processes

Evolution of squeezed states under the Fock-Darwin Hamiltonian

We develop a complete analytical description of the time evolution of squeezed states of a charged particle under the Fock-Darwin Hamiltonian and a time-dependent electric field. This result generalises a relation obtained by Infeld and Pleba\'nski for states of the one-dimensional harmonic oscillator. We relate the evolution of a state-vector subjected to squeezing to that of state which is not subjected to squeezing and for which the time-evolution under the simple harmonic oscillator dynamics is known (e.g. an eigenstate of the Hamiltonian). A corresponding relation is also established for the Wigner functions of the states, in view of their utility in the analysis of cold-ion experiments. In an appendix, we compute the response functions of the FD Hamiltonian to an external electric field, using the same techniques as in the main text

Fatty acids profile of Serra da Estrela PDO cheeses and respective atherogenic and thrombogenic indices

Purpose: This study aims to determine the physicochemical and fatty acids composition of Serra da Estrela cheese (SEC), as well as health-related lipid indices, like the atherogenic and thrombogenic indices, and to evaluate the influence of producer, geographical origin and production date. Design/methodology/approach: All 24 SEC produced between November 2017 and March 2018 were collected at selected certified producers and analyzed by NIR spectrophotometer and by GC. Data were statistically evaluated by chemometric tools. Findings: In all evaluated SEC, 23 fatty acids were quantified. Cheese origin influenced nutritional and health-related lipid indices). The cheeses were characterized by a relative high abundance of saturated fatty acids (67-76%), followed by a medium content of monounsaturated fatty acids (17-25%) and by low level of polyunsaturated fatty acids (5-7%). A putative positive association between cheese consumption and healthy lipid indices could be reached. Practical implications The contents of some medium and long chain fatty acids as well as of nutritional and health indices were influenced by cheese producer, geographical origin and production date pointing out the need for standardizing production procedures. Social implications The SEC plays a key role in the local economy, being an endogenous product with unique sensory characteristics and nutritional potential, for which the knowledge of the lipids profile and health indices is of utmost relevance. Originality/value SEC is an iconic Portuguese cheese with Protected Designation of Origin. Based on the results, like health-related lipid indices, evaluated for the first time, a positive association between cheese consumption and healthy lipid indices could be envisaged.This work was financially supported by Associate Laboratory LSRE-LCM - UID/EQU/50020/2019, strategic funding UID/BIO/04469/2019-CEB and BioTecNorte operation (NORTE-01-0145-FEDER000004), and strategic project PEst-OE/AGR/UI0690/2014–CIMO funded by national funds through FCT/MCTES (PIDDAC). The authors would also like to acknowledge the funding provided by the approved Project, with reference 02/SAICT/2016/23290, entitled Characterization and Valorization of QSE PDO and its ability for health promotion (QCLASSE), financed by FCT.info:eu-repo/semantics/publishedVersio

Zigzag graphene nanoribbon edge reconstruction with stone-wales defects

In this paper, we study zigzag graphene nanoribbons with edges reconstructed with Stone-Wales defects, by means of an empirical (first-neighbor) tight-binding method, with parameters determined by ab initio calculations of very narrow ribbons. We explore the characteristics of the electronic band structure with a focus on the nature of edge states. Edge reconstruction allows the appearance of a new type of edge states. They are dispersive, with nonzero amplitudes in both sublattices; furthermore, the amplitudes have two components that decrease with different decay lengths with the distance from the edge; at the Dirac points one of these lengths diverges, whereas the other remains finite, of the order of the lattice parameter. We trace this curious effect to the doubling of the unit cell along the edge, brought about by the edge reconstruction. In the presence of a magnetic field, the zero-energy Landau level is no longer degenerate with edge states as in the case of the pristine zigzag ribbon.Fundacao para a Ciência e a Tecnologia (FCT) SFRH/BD/44456/2008.FEDER - Programa Operacional Factores de Competitividade - COMPET