Thermodynamic potential of the Periodic Anderson Model with the X-boson method: Chain Approximation

The Periodic Anderson Model (PAM) in the $U\to\infty$ limit has been studied in a previous work employing the cumulant expansion with the hybridization as perturbation (M. S. Figueira, M. E. Foglio and G. G. Martinez, Phys. Rev. B \textbf{50}, 17933 (1994)). When the total number of electrons $N_{t}$ is calculated as a function of the chemical potential $\mu$ in the ``Chain Approximation'' (CHA), there are three values of the chemical potential $\mu$ for each $N_{t}$ in a small interval of $N_{t}$ at low $T$ (M. S Figueira, M. E Foglio, Physica A 208 (1994)). We have recently introduced the ``X-boson'' method, inspired in the slave boson technique of Coleman, that solves the problem of non conservation of probability (completeness) in the CHA as well as removing the spurious phase transitions that appear with the slave boson method in the mean field approximation. In the present paper we show that the X-boson method solves also the problem of the multiple roots of $N_{t}(\mu)$ that appear in the CHA.Comment: 13 pages, 6 figures e-mails: [email protected], [email protected], [email protected]

Cumulant Expansion Of The Periodic Anderson Model: General Derivation

We extend to the periodic Anderson model (PAM) the diagrammatic expansion in cumulants that was employed by Hubbard to study his model of a narrow band of strongly correlated electrons. The PAM is a lattice of localized and strongly correlated electrons with spin one-half and without orbital degeneracy, hybridized with a wide band of uncorrelated conduction electrons. We have extended the model by considering localized electronic states with an arbitrary scheme of energy levels: this extension would be useful to study intermediate valence compounds of Eu or Tm with the present formalism. We give the rules for the diagrammatic calculation of the grand canonical potential and of the Greens functions for the general model: only connected diagrams appear in those calculations and the lattice sums are unrestricted. To generate the cumulant averages it was necessary to employ external fields that are Grassman variables. We have found a simple way to extend the diagrammatic rules to the 0 case. The absence of excluded site restrictions, that leads to complicated excluded volume problems in other treatments, and the existence of linked cluster expansions, are features of the cumulant expansion. As an application of the present method, we have calculated the occupation numbers of localized and conduction electrons for the PAM in the limit of infinite Coulomb repulsion (U). © 1994 The American Physical Society.5024179331795

X-boson cumulant approach to the periodic Anderson model

The Periodic Anderson Model (PAM) can be studied in the infinite U limit by employing the Hubbard X operators to project out the unwanted states. We have already studied this problem employing the cumulant expansion with the hybridization as perturbation, but the probability conservation of the local states (completeness) is not usually satisfied when partial expansions like the Chain Approximation (CHA) are employed. Here we treat the problem by a technique inspired in the mean field approximation of Coleman's slave-bosons method, and we obtain a description that avoids the unwanted phase transition that appears in the mean-field slave-boson method both when the chemical potential is greater than the localized level Ef at low temperatures (T) and for all parameters at intermediate T.Comment: Submited to Physical Review B 14 pages, 17 eps figures inserted in the tex

Consumers' perceptions and consumption behaviour concerning red fruits

Consumers' concern for disease prevention makes them aware of the importance to follow a healthy diet. Red fruits are known for their potential health benefits, namely due to their richness in antioxidants, vitamins and minerals. To assess consumers’ perception of red fruits purchase, conservation, preparation and consumption habits and their potential health benefits. A questionnaire was applied and distributed through e-mails and social media. From January to February of 2023, 507 individuals answered this survey. It focused on individuals’ perception of red fruits consumption and purchase habits; reasons, frequency and season of consumption; preparation and conservation procedures and potential health benefits. Among all participants, 62.7% were aged between 18-29 years, 75.3% were females and 60.4% were from Lisbon. The majority had higher education (79.6%) and a considerable number had health qualifications (36.1%). 387 participants claimed to frequently consume red fruits. Those who do not consume essentially declared high price as the main reason (60.0%). Most people purchase red fruits at super and hypermarkets (88.4%), eat them mostly fresh in spring and summer, and keep them in the fridge until consumption. Strawberry was the most frequently consumed and cranberry was the least one. Vitamins (92.1%) and anthocyanins (44.4%) were the most common substances related to red berries. 49.1% of the participants considered red fruits to be more beneficial than others, associating them with antioxidant effects (87.8%), general health and well-being (69.6%), and prevention of diseases (71.8%) like cardiovascular diseases (73.9%) and cancer (57.4%). Our findings suggest that most of this population consumes red fruits. It was verified a reasonable knowledge of their health benefits; however, several did not recognize their advantages, even having higher education. It is essential to enhance the spread of scientific information regarding the potential health benefits associated with the consumption of red fruits.this work was financially supported by INSA, I.P., under the project TradFRUIT (2012DAN668) and by European Union (FEDER funds through COMPETE), under the Partnership Agreement PT2020, and National Funds (FCT, Foundation for Science and Technology) through projects UIDB/50006/2020 and by AgriFood XXI I&D&I project (NORTE-01-0145-FEDER-000041) co-financed by European Regional Development Fund (ERDF), through the NORTE 2020 (Programa Operacional Regional do Norte 2014/2020).info:eu-repo/semantics/publishedVersio

X-boson Cumulant Approach To The Topological Kondo Insulators

In this work we present a generalization of our previous work of the X-boson approach to the periodic Anderson model (PAM), adequate to study a novel class of intermetallic 4f and 5f orbitals materials: the topological Kondo insulators, whose paradigmatic material is the compound SmB6. For simplicity, we consider a version of the PAM on a 2D square lattice, adequate to describe Ce-based compounds in two dimensions. The starting point of the model is the 4f - Ce ions orbitals, with J 5/2 multiplet, in the presence of spin-orbit coupling. Our technique works well for all of the parameters of the model and avoids the unwanted phase transitions of the slave boson mean field theory. We present a critical comparison of our results with those of the usual slave boson method, that has been intensively used to describe this class of materials. We also obtain a new valence first order transition which we attribute to the dependence of the hybridization.568DIB; Dirección de Investigación, Universidad Nacional de ColombiaColeman, P., (1984) Phys. Rev., 29 (6), p. 3035Dzero, M., Sun, K., Galitski, V., Coleman, P., (2010) Phys. Rev. Lett., 104 (10), p. 106408Dzero, M., Sun, K., Coleman, P., Galitski, V., (2012) Phys. Rev., 85 (4), p. 045130Alexandrov, V., Dzero, M., Coleman, P., (2013) Phys. Rev. Lett., 111 (22), p. 226403Tran, M.T., Takimoto, T., Kim, K.S., (2012) Phys. Rev., 85 (12), p. 125128Legner, M., Rueg, A., Sigrist, M., Phys. Rev., 89, p. 085110Werner, J., Assaad, F.F., (2013) Phys. Rev., 88 (3), p. 035113Franco, R., Figueira, M.S., Foglio, M.E., (2003) Phys. Rev., 66 (4), p. 045112Steglich, F., Geibel, C., Gloss, K., Olesch, G., Schank, C., Wassilew, C., Loidl, A., Stewart, G.F., (1994) J. Low Temperature Phys., 95 (1-2), p. 3Derr, J., Knebel, G., Lapertot, G., Salce, B., Measson, M.-A., Flouquet, J., (2006) J. Phys.: Condens. Matter, 18 (6), p. 2089Natoli, V.D., Cohen, H.M., Fornberg, B., (1996) J. Computacional Phys., 126 (1), p. 9

Fano resonance in electronic transport through a quantum wire with a side-coupled quantum dot: X-boson treatment

The transport through a quantum wire with a side coupled quantum dot is studied. We use the X-boson treatment for the Anderson single impurity model in the limit of $U=\infty$. The conductance presents a minimum for values of T=0 in the crossover from mixed-valence to Kondo regime due to a destructive interference between the ballistic channel associated with the quantum wire and the quantum dot channel. We obtain the experimentally studied Fano behavior of the resonance. The conductance as a function of temperature exhibits a logarithmic and universal behavior, that agrees with recent experimental results.Comment: 6 pages, 10 eps figs., revtex

Determinação do bisfenol A e éter diglicidílico do bisfenol A em alimentos enlatados

O Bisfenol A (BPA) é um composto químico produzido a larga escala. De facto a produção mundial de BPA por ano é superior a 3,5 milhões de toneladas. Devido às suas características de resistência e elasticidade este composto é utilizado na produção de diversos produtos, como policarbonato e resinas epóxi. As resinas epóxi são obtidas comercialmente a partir da reação entre o bisfenol A e a epicloridrina que resulta no éter diglicidílico de bisfenol A, também conhecido como BADGE e estão presentes no revestimento de embalagens de alimentos enlatados. A União Europeia estabeleceu um limite de migração específica (LME) para o BPA de 0,6 mg/kg de alimento (Regulamento (EU) nº 10/2011 da comissão 2011). O presente trabalho teve como propósito a determinação de BPA e de BADGE em materiais em contato com alimentos. Neste sentido, procedeu-se ao desenvolvimento, otimização e validação de um método para determinação destes dois compostos por Cromatografia Líquida de Ultra Eficiência acoplada a um Detetor de Fluorescência (UHPLC-FL). Foram analisadas amostras de pescado enlatado, de diferentes marcas, disponíveis no mercado português, no período de Janeiro a Julho de 2017. Os parâmetros de validação determinados foram a especificidade, linearidade e gama de trabalho, limite de deteção, limite de quantificação, repetibilidade, precisão e exatidão. Os valores da Precisão (expressos em % de desvio padrão relativo) encontram-se em conformidade com os citérios de validação para métodos analíticos, tendo sido sempre inferiores a 4,9% e a recuperação foi aceitável nos 4 níveis de fortificação testados. Verificou-se que todas as amostras cumpriram com os limites máximos permitidos pela legislação europeia em vigor, garantindo assim a segurança do consumo destes alimentos.O presente trabalho insere-se no projeto “Desenvolvimento de metodologias para avaliação de componentes de embalagens alimentares poliméricas e determinação das suas propriedades estruturais e mecânicas (2016 DAN 1283), financiado pelo Instituto Nacional de Saúde Doutor Ricardo Jorge.N/

Thermodynamic properties of the periodic Anderson model:X-boson treatment

We study the specific dependence of the periodic Anderson Model (PAM) in the limit of $U=\infty$ employing the X-boson treatment in two fifferent regimes of the PAM: the heavy fermion Kondo (HF-K) and the heavy fermion local magnetic regime (HF-LMM). We obtain a multiple peak structure for the specific heat in agreement with experimental results as well as the increase of the electronic effective mass at low temperatures associated with the HF-K regime. The entropy per site at low T tends to zero in the HF-K regime, corresponding to a singlet ground state, and it tends to $k_{B}ln(2)$ in the HF-LMM, corresponding to a doublet ground state at each site. The linear coefficient $\gamma(T)=C_{v}/T$ of the specific heat qualitatively agrees with the experimental results obtained for differents materials in the two regimes considered here.Comment: 9 pages, 14 figure

Evidence for a mixed mass composition at the `ankle' in the cosmic-ray spectrum

We report a first measurement for ultra-high energy cosmic rays of the correlation between the depth of shower maximum and the signal in the water Cherenkov stations of air-showers registered simultaneously by the fluorescence and the surface detectors of the Pierre Auger Observatory. Such a correlation measurement is a unique feature of a hybrid air-shower observatory with sensitivity to both the electromagnetic and muonic components. It allows an accurate determination of the spread of primary masses in the cosmic-ray flux. Up till now, constraints on the spread of primary masses have been dominated by systematic uncertainties. The present correlation measurement is not affected by systematics in the measurement of the depth of shower maximum or the signal in the water Cherenkov stations. The analysis relies on general characteristics of air showers and is thus robust also with respect to uncertainties in hadronic event generators. The observed correlation in the energy range around the `ankle' at $\lg(E/{\rm eV})=18.5-19.0$ differs significantly from expectations for pure primary cosmic-ray compositions. A light composition made up of proton and helium only is equally inconsistent with observations. The data are explained well by a mixed composition including nuclei with mass $A > 4$. Scenarios such as the proton dip model, with almost pure compositions, are thus disfavoured as the sole explanation of the ultrahigh-energy cosmic-ray flux at Earth.Comment: Published version. Added journal reference and DOI. Added Report Numbe