Spin-glass phase transition and behavior of nonlinear susceptibility in the Sherrington-Kirkpatrick model with random fields

The behavior of the nonlinear susceptibility $\chi_3$ and its relation to the spin-glass transition temperature $T_f$, in the presence of random fields, are investigated. To accomplish this task, the Sherrington-Kirkpatrick model is studied through the replica formalism, within a one-step replica-symmetry-breaking procedure. In addition, the dependence of the Almeida-Thouless eigenvalue $\lambda_{\rm AT}$ (replicon) on the random fields is analyzed. Particularly, in absence of random fields, the temperature $T_f$ can be traced by a divergence in the spin-glass susceptibility $\chi_{\rm SG}$, which presents a term inversely proportional to the replicon $\lambda_{\rm AT}$. As a result of a relation between $\chi_{\rm SG}$ and $\chi_3$, the latter also presents a divergence at $T_f$, which comes as a direct consequence of $\lambda_{\rm AT}=0$ at $T_f$. However, our results show that, in the presence of random fields, $\chi_3$ presents a rounded maximum at a temperature $T^{*}$, which does not coincide with the spin-glass transition temperature $T_f$ (i.e., $T^* > T_f$ for a given applied random field). Thus, the maximum value of $\chi_3$ at $T^*$ reflects the effects of the random fields in the paramagnetic phase, instead of the non-trivial ergodicity breaking associated with the spin-glass phase transition. It is also shown that $\chi_3$ still maintains a dependence on the replicon $\lambda_{\rm AT}$, although in a more complicated way, as compared with the case without random fields. These results are discussed in view of recent observations in the LiHo$_x$Y$_{1-x}$F$_4$ compound.Comment: accepted for publication in PR

Statics and dynamics of an Ashkin-Teller neural network with low loading

An Ashkin-Teller neural network, allowing for two types of neurons is considered in the case of low loading as a function of the strength of the respective couplings between these neurons. The storage and retrieval of embedded patterns built from the two types of neurons, with different degrees of (in)dependence is studied. In particular, thermodynamic properties including the existence and stability of Mattis states are discussed. Furthermore, the dynamic behaviour is examined by deriving flow equations for the macroscopic overlap. It is found that for linked patterns the model shows better retrieval properties than a corresponding Hopfield model.Comment: 20 pages, 6 figures, Latex with postscript figures in one tar.gz fil

Uso múltiplo da água e lâminas de irrigação da bananeira FHIA 18 nas condições de semiárida.

Este trabalho objetivou avaliar a contribuição nutricional do uso múltiplo da água da piscicultura na irrigação da bananeira cv. Fhia 18. O experimento foi desenvolvido no Projeto Piloto de Fruticultura Irrigada do Vale de Parnaíba, localizado no município de Santa Rosa do Piauí, região semi-árida do Piauí

Classical Infinite-Range-Interaction Heisenberg Ferromagnetic Model: Metastability and Sensitivity to Initial Conditions

A N-sized inertial classical Heisenberg ferromagnet, which consists in a modification of the well-known standard model, where the spins are replaced by classical rotators, is studied in the limit of infinite-range interactions. The usual canonical-ensemble mean-field solution of the inertial classical $n$-vector ferromagnet (for which $n=3$ recovers the particular Heisenberg model considered herein) is briefly reviewed, showing the well-known second-order phase transition. This Heisenberg model is studied numerically within the microcanonical ensemble, through molecular dynamics.Comment: 18 pages text, and 7 EPS figure

SIG como ferramenta de planejamento de uso de águas subterrâneas no município de Santa Rosa do Piauí-PI.

Este trabalho teve como objetivo avaliar o aquífero subterrâneo do Município de Santa Rosa do Piauí-PI delimitando com uso de ferramentas de geoprocessamento e SIG a superfície potenciométrica, a variação de STD e a descarga de sólidos a partir de dados medidos de poços instalados no município..

Produção simultânea de -fructofuranosidase e fructo-oligossacarídeos por Penicillium citreonigrum URM 4459

O objetivo deste trabalho foi a produção simultânea de -Frutofuranosidase (FFase) e frutooligossacarídeos (FOS) por P. citreonigrum utilizando um planejamento fatorial completo. Para isso, o fungo foi cultivado em meio rico em sacarose (20% p/v) a 150 rpm. As condições de tempo de fermentação, temperatura, pH e concentração de extrato de levedura foram definidas utilizando um planejamento fatorial. Ao fim da fermentação, o sobrenadante obtido por filtração foi utilizado para quantificação de FFase e FOS. Todas as variáveis independentes estudadas exerceram efeito estatisticamente significativo sob a produção de FFase. Por outro lado, apenas as variáveis tempo de fermentação e temperatura exerceram efeito significativo sob a produção do FOS. As condições ideais para produção simultânea de FFase e FOS foram obtidas na região dos pontos centrais, onde obteve-se uma produção média de 93,49 g/L de FOS e uma atividade de 260,40 U/mL de FFase

Stress distribution and the fragility of supercooled melts

We formulate a minimal ansatz for local stress distribution in a solid that includes the possibility of strongly anharmonic short-length motions. We discover a broken-symmetry metastable phase that exhibits an aperiodic, frozen-in stress distribution. This aperiodic metastable phase is characterized by many distinct, nearly degenerate configurations. The activated transitions between the configurations are mapped onto the dynamics of a long range classical Heisenberg model with 6-component spins and anisotropic couplings. We argue the metastable phase corresponds to a deeply supercooled non-polymeric, non-metallic liquid, and further establish an order parameter for the glass-to-crystal transition. The spin model itself exhibits a continuous range of behaviors between two limits corresponding to frozen-in shear and uniform compression/dilation respectively. The two regimes are separated by a continuous transition controlled by the anisotropy in the spin-spin interaction, which is directly related to the Poisson ratio $\sigma$ of the material. The latter ratio and the ultra-violet cutoff of the theory determine the liquid configurational entropy. Our results suggest that liquid's fragility depends on the Poisson ratio in a non-monotonic way. The present ansatz provides a microscopic framework for computing the configurational entropy and relaxational spectrum of specific substances.Comment: 11 pages, 5 figures, Final version published in J Phys Chem

Comment on "Critique of q-entropy for thermal statistics" by M. Nauenberg

It was recently published by M. Nauenberg [1] a quite long list of objections about the physical validity for thermal statistics of the theory sometimes referred to in the literature as {\it nonextensive statistical mechanics}. This generalization of Boltzmann-Gibbs (BG) statistical mechanics is based on the following expression for the entropy: S_q= k\frac{1- \sum_{i=1}^Wp_i^q}{q-1} (q \in {\cal R}; S_1=S_{BG} \equiv -k\sum_{i=1}^W p_i \ln p_i) . The author of [1] already presented orally the essence of his arguments in 1993 during a scientific meeting in Buenos Aires. I am replying now simultaneously to the just cited paper, as well as to the 1993 objections (essentially, the violation of "fundamental thermodynamic concepts", as stated in the Abstract of [1]).Comment: 7 pages including 2 figures. This is a reply to M. Nauenberg, Phys. Rev. E 67, 036114 (2003

OC33 Chromatographic approaches to study pine nut skin: exploitation of its composition and bioactivities

Pine nut skin (PNS) is an unexploited and uncharacterized by-product recovered during pine nut processing. The exploitation of by-products as sources of valuable compounds agrees with the current demand for the reduction of waste, and a transition to more sustainable production and consumption1. Therefore, PNS characterization and bioactive potentialities were assessed. The utilization of several chromatographic techniques allowed the characterization of PNS phenolic compounds (HPLC-DAD-UV and HPLC-DAD-ESI-MSn), and the carbohydrates quantification and structural characterization, after specific derivatization (GC-FID and GC-MS). PNS subcritical water extraction using microwave was optimized and the obtained extracts, separated into low-molecularweight (rich in phenolic compounds) and high-molecular-weight (rich in carbohydrates), were evaluated regarding their digestibility and prebiotic activity. The prebiotic potential was assessed by quantifying the short-chain fatty acids (HPLC-UV) produced after the in vitro faecal fermentation. HPLC-DAD-ESI-MSn allowed to identify PNS phenolic compounds, namely protocatechuic, p-coumaric, and caffeic acids, while HPLC-DAD-UV enabled the monomers identification of proanthocyanidins ((epi)catechins) and hydrolysable tannins (protocatechuic acid), after acid methanolysis. GC techniques allowed to disclose the polysaccharides structures (xyloglucans and pectic polysaccharides) and their degradation by microbiota. The fermentation of both extracts rich in phenolic compounds and rich in polysaccharides resulted in an increased production of acetic, propionic, and butyric acids when compared to the commercial prebiotic inulin, proposing these PNS extracts as prebiotic agents.The work was supported through the projects UIDB/50006/2020 and UIDP/50006/2020, funded by FCT/MCTES through national funds. Soraia P. Silva, Alondra González and Dalila Roupar thank FCT/MCTES and ESF through NORTE 2020 for their PhD grants (ref. SFRH/BD/136471/2018, SFRH/BD/06268/2021 and SFRH/DB/139884/2018 respectively). Elisabete Coelho thanks the research contract (CDL-CTTRI-88-ARH/2018 – REF. 049-88-ARH/2018) funded by national funds (OE), through FCT, in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19. Clarisse Nobre acknowledges FCT for the assistant research contract 2021.01234.CEECIND.info:eu-repo/semantics/publishedVersio

Caracterização morfoagronômica de acessos de mamoeiro do banco de germoplasma da Embrapa Mandioca e Fruticultura.

Resumo: O objetivo deste trabalho foi realizar uma caracterização morfoagronômica dos acessos do Banco Ativo de Germoplasma (BAG) de mamoeiro da Embrapa Mandioca e Fruticultura, por meio do estudo da diversidade genética e da análise multivariada. A caracterização foi feita em 92 acessos do germoplasma de mamoeiro, com 20 descritores, dos quais 9 eram quantitativos e, 11, qualitativos. Realizou-se uma análise descritiva dos caracteres quantitativos, dos quais se destacaram acessos com 20° Brix de sólidos solúveis e 5,5 kgf cm-2 de firmeza do fruto. A análise multivariada dos 20 descritores resultou na formação de três grupos. Os acessos apresentaram diversidade moderada. Os acessos CMF006, CMF054, CMF056, CMF067, CMF072, CMF082, CMF115, CMF131, CMF188 e CMF204 destacaram-se quanto ao teor de sólidos solúveis, firmeza de fruto, fibrosidade da polpa, altura de planta e altura dos primeiros frutos. Distribuídos equitativamente nos grupos 'Formosa' e 'Solo', esses acessos são em sua maioria oriundos de cultivares brasileiras. Apesar da estreita base genética do mamoeiro, o estudo indicou a presença de uma diversidade moderada e de importante variabilidade genética em acessos de interesse agronômico. Portanto, o BAG do mamoeiro da Embrapa Mandioca e Fruticultura pode atender às demandas de melhoramento genético e dos produtores rurais. Abstract: The objective of this work was to perform a morphoagronomic characterization of the papaya accessions of the active germplasm bank (AGB) of Embrapa Mandioca e Fruticultura, through the study of genetic diversity and multivariate analysis. Ninetytwo papaya accessions were characterized in 92 accessions of the papaya germplasm, using 20 descriptors, from which 9 were related to quantitative traits, and 11 related to qualitative ones. A descriptive analysis of the quantitative traits was performed, from which accessions with 20 °Brix soluble solids and 5.5 kgf cm-2 fruit firmness stood out. The multivariate analysis of the 20 descriptors resulted in the formation of three groups. The accessions showed moderate diversity. The accessions CMF006, CMF054, CMF056, CMF067, CMF072, CMF082, CMF115, CMF131, CMF188, and CMF204 stood out for soluble solids, fruit firmness, pulp fibrosity, plant height, and height of the first fruits. Equally distributed in the 'Formosa' and 'Solo' groups, these most accessions originated from Brazilian cultivars. Despite the narrow genetic basis of papaya, the study showed a moderate diversity and an important genetic variability in accessions of agronomic interest. Therefore, the papaya ABG of Embrapa Mandioca e Fruticultura can meet the demands for genetic improvement and the expectations of farmers.Título em inglês: Morphoagronomic characterization of papaya accessions of the active germplasm bank of Embrapa Mandioca e Fruticultura