Unusual low-temperature behavior in the half-filled band of the one-dimensional extended Hubbard model in atomic limit.

Recently, a kind of finite-temperature pseudotransition was observed in several quasi-one-dimensional models. In this work, we consider a genuine one-dimensional extended Hubbard model in the atomic limit, influenced by an external magnetic field and with the arbitrary number of particles controlled by the chemical potential. The one-dimensional extended Hubbard model in the atomic limit was initially studied in the seventies and has been investigated over the past decades, but it still surprises us today with its fascinating properties. We rigorously analyze its low-temperature behavior using the transfer matrix technique and provide accurate numerical results. Our analysis confirms that there is an anomalous behavior in the half-filled band, specifically occurring between the alternating pair (AP) and paramagnetic (PM) phases at zero temperature. Previous investigations did not deeply identify this anomalous behavior, maybe due to the numerical simplicity of the model, but from an analytical point of view this is not so easy to manipulate algebraically because one needs to solve an algebraic cubic equation. In this study, we explore this behavior and clearly distinguish the pseudotransition, which could easily be mistaken with a real phase transition. This anomalous behavior mimics features of both first- and second-order phase transitions. However, due to its nature, we cannot expect a finite-temperature phase transition in this model.

Residual entropy and magnetocaloric effect in a diluted sawtooth spin model of hole-doped CuO chains.

Ground-state and magnetocaloric properties of a site-diluted sawtooth magnetic chain in the presence of an external magnetic field are exactly investigated by using the transfer-matrix method. The model captures the main magnetic interactions along CuO chains present in some hole-doped cuprates. The ground-state diagram is exhibited and analytical expressions for the residual entropy within each ground state and along the transition lines are derived. We explicitly discuss the role of the underlying pairing correlations and the entropy maximization principle. The isothermal entropy change is determined as a function of interaction parameters, doping concentration, and magnetic-field amplitude. Normal and inverse magnetocaloric effects are reported. Adiabatic demagnetization curves are discussed in connection with configurational and spin contributions to the residual entropy.

Low-temperature pseudo-phase-transition in an extended Hubbard diamond chain.

We consider the extended Hubbard diamond chain with an arbitrary number of particles driven by chemical potential. The interaction between dimer diamond chain and nodal couplings is considered in the atomic limit (no hopping), whereas the dimer interaction includes the hopping term. We demonstrate that this model exhibits a pseudo-transition effect in the low-temperature regime. Here, we explore the pseudo-transition rigorously by analyzing several physical quantities. The internal energy and entropy depict sudden, although continuous, jumps which closely resembles discontinuous or first-order phase-transition. At the same time, the correlation length and specific heat exhibit astonishing strong sharp peaks quite similar to a second-order phase-transition. We associate the ascending and descending parts of the peak with power-law "pseudo-critical" exponents. We determine the pseudo-critical exponents in the temperature range where these peaks are developed, namely, ν=1 for the correlation length and α=3 for the specific heat. We also study the behavior of the electron density and isothermal compressibility around the pseudo-critical temperature.

Peculiarities in pseudo-transitions of a mixed spin-(1/2, 1) Ising-Heisenberg double-tetrahedral chain in an external magnetic field.

Recently, it has been rigorously verified that several one-dimensional (1D) spin models may exhibit a peculiar pseudo-transition accompanied with anomalous response of thermodynamic quantities in a close vicinity of pseudo-critical temperature. In the present work we will introduce and exactly solve a mixed spin-(1/2,1) Ising-Heisenberg double-tetrahedral chain in an external magnetic field as another particular example of 1D lattice-statistical model with short-range interactions that displays a pseudo-transition of this type. The investigated model exhibits at zero temperature three ferrimagnetic phases, three frustrated phases, and one saturated paramagnetic phase. The ground-state phase diagram involves five unusual interfaces (phase boundaries), at which the residual entropy per site equals to a larger entropy of one of two coexisting phases. Four such interfaces are between a non-degenerate ferrimagnetic phase and a macroscopically degenerate frustrated phase, while one interface is between two non-degenerate ferrimagnetic phases. Though thermal excitations typically destroy all fingerprints of zero-temperature phase transitions of 1D lattice-statistical models with short-range forces, the mixed spin-(1/2,1) Ising-Heisenberg double-tetrahedral chain is quite robust with respect to thermal excitations and it displays peculiar pseudo-transitions close to all five aforementioned interfaces.

Validation of a reaction volume reduction protocol for analysis of Y chromosome haplotypes targeting DNA databases.

The use of Y chromosome haplotypes, important for the detection of sexual crimes in forensics, has gained prominence with the use of databases that incorporate these genetic profiles in their system. Here, we optimized and validated an amplification protocol for Y chromosome profile retrieval in reference samples using lesser materials than those in commercial kits. FTA® cards (Flinders Technology Associates) were used to support the oral cells of male individuals, which were amplified directly using the SwabSolution reagent (Promega). First, we optimized and validated the process to define the volume and cycling conditions. Three reference samples and nineteen 1.2 mm-diameter perforated discs were used per sample. Amplification of one or two discs (samples) with the PowerPlex® Y23 kit (Promega) was performed using 25, 26, and 27 thermal cycles. Twenty percent, 32%, and 100% reagent volumes, one disc, and 26 cycles were used for the control per sample. Thereafter, all samples (N = 270) were amplified using 27 cycles, one disc, and 32% reagents (optimized conditions). Data was analyzed using a study of equilibrium values between fluorophore colors. In the samples analyzed with 20% volume, an imbalance was observed in peak heights, both inside and in-between each dye. In samples amplified with 32% reagents, the values obtained for the intra-color and inter-color standard balance calculations for verification of the quality of the analyzed peaks were similar to those of samples amplified with 100% of the recommended volume. The quality of the profiles obtained with 32% reagents was suitable for insertion into databases.

Kinetic study of biodegradation of BTX compounds in mono- and multicomponent systems in reactor with immobilized biomass.

In this study, kinetic parameters were determined for the biodegradation of BTX compounds in a fixed-bed reactor with immobilized biomass, fed with mono- and multicomponent systems. The parameter estimation was achieved through an algorithm using the finite volume method. Different kinetic models were evaluated. The Monod model proved to be suitable to predict the experimental data for the biodegradation individual BTX compound. In multicomponent systems, it was found that the presence of more than one compound tends to cause competitive inhibition. To identify the models that best fit the experimental data, a statistical analysis using the F test was applied. For the two- and three-component systems the presence of more than one compound tends to cause competitive inhibition. In this study, it was possible to predict kinetic parameters in mono- and multicomponent systems as well as different operation conditions for a fixed-bed reactor with immobilized biomass.

Echinostomes in Felid Coprolites from Brazil.

The first record of Echinostoma (Trematoda: Echinostomatidae) in coprolites was from a mummified human body in Minas Gerais State, Brazil. The finding raised questions on this parasite's incidence in prehistoric populations and the natural hosts of each species in remote times. Echinostomes occur worldwide and, despite the wide range of hosts, there is no record of Echinostomatidae in felines in Brazil. This study reports the finding of Echinostomatidae eggs in felid coprolites in the Furna do Estrago Archaeological Site, located in Pernambuco State in the Brazilian semiarid. Despite the possibility of false parasitism, the finding expands the distribution of this Digenea in remote times and raises the hypothesis of other cases of echinostomiasis in pre-Colombian populations.

An Evaluation of Kinetic Models in the Biodesulfurization of Synthetic Oil by Rhodococcus erythropolis ATCC 4277.

Biodesulfurization is an eco-friendly technology applied in the removal of sulfur from fossil fuels. This technology is based on the use of microorganisms as biocatalysts to convert the recalcitrant sulfur compounds into others easily treatable, as sulfides. Despite it has been studied during the last decades, there are some unsolved questions, as per example the kinetic model which appropriately describes the biodesulfurization globally. In this work, different kinetic models were tested to a batch desulfurization process using dibenzothiophene (DBT) as a model compound, n-dodecane as organic solvent, and Rhodococcus erythropolis ATCC 4277 as biocatalyst. The models were solved by ODE45 function in the MATLAB. Monod model was capable to describe the biodesulfurization process predicting all experimental data with a very good fitting. The coefficients of determination achieved to organic phase concentrations of 20, 80, and 100 % (v/v) were 0.988, 0.995, and 0.990, respectively. R. erythropolis ATCC 4277 presented a good affinity with the substrate (DBT) since the coefficients of saturation obtained to reaction medium containing 20, 80, and 100 % (v/v) were 0.034, 0.07, and 0.116, respectively. This kinetic evaluation provides an improvement in the development of biodesulfurization technology because it showed that a simple model is capable to describe the throughout process.

Desulfurization and denitrogenation of heavy gas oil by Rhodococcus erythropolis ATCC 4277.

Some of the noxious atmospheric pollutants such as nitrogen and sulfur dioxides come from the fossil fuel combustion. Biodesulfurization and biodenitrogenation are processes which remove those pollutants through the action of microorganisms. The ability of sulfur and nitrogen removal by the strain Rhodococcus erythropolis ATCC 4277 was tested in a biphasic system containing different heavy gas oil concentrations in a batch reactor. Heavy gas oil is an important fraction of petroleum, because after passing through, the vacuum distillation is incorporated into diesel oil. This strain was able to remove about 40% of the nitrogen and sulfur present in the gas heavy oil. Additionally, no growth inhibition occurred even when in the presence of pure heavy gas oil. Results present in this work are considered relevant for the development of biocatalytic processes for nitrogen and sulfur removal toward building feasible industrial applications.

Viabilidade econômica da inclusão de óleo de girassol em dieta à base de cana-de-açúcar para vacas em lactação / Economic viability of feeding different levels of sunflower oil in sugarcane-based diets to lactating cows

Objetivou-se avaliar a viabilidade econômica da produção de leite de vacas Holandês x Gir, pela inclusão de níveis crescentes de óleo de girassol (0,0; 1,5; 3,0 e 4,5 por cento) na matéria seca de dietas baseadas em cana-de-açúcar. Os dados utilizados no estudo foram obtidos de experimento realizado com 12 vacas Holandês x Gir, multíparas, com produção média de 18,2kg/dia de leite, distribuídas em três quadrados latinos 4 x 4, conforme a produção de leite, a ordem de lactação e o peso corpóreo. As dietas foram isoproteicas, fornecidas ad libitum na forma de mistura total (relação volumoso:concentrado de 60:40, base matéria seca), e os consumos das vacas determinados diariamente. As produções individuais diárias de leite foram registradas, e sua composição foi analisada quanto aos teores de gordura, proteína e ácidos graxos. A viabilidade econômica foi realizada considerando-se os preços dos ingredientes fornecidos e o consumo diário da dieta de cada tratamento. O benefício econômico foi obtido pela diferença entre a receita, com a venda do leite, e o custo com alimentação dos animais. O pagamento por qualidade foi estimado pela média de oito sistemas utilizados por empresas do ramo de laticínios, com base nos teores de gordura, proteína e no volume de leite. A dieta sem inclusão de OG foi a que proporcionou maior benefício econômico. A inclusão de OG nas dietas baseadas em cana-de-açúcar não foi viável, economicamente, devido aos gastos adicionais com OG e às penalizações resultantes da redução dos teores de proteína e de gordura do leite.(AU)

The aim of this study was to evaluate the economic viability of the milk yield of Holstein x Gir cows by the addition of growing levels of sunflower oil (SO) (0.0, 1.5, 3.0 and 4.5 percent) in the dry matter of sugar-cane based diets. The data utilized in the study were obtained from an experiment conducted with 12 multiparous Holstein x Gir cows, with average yield of 18.2kg/day of milk, distributed into three 4 x 4 Latin squares according to milk yield, lactation order and body weight. The diets were isoprotein, a total mixture fed at libitum (ratio roughage concentrate of 60:40, dry matter basis) and cow consumption was determined daily. The individual milk yields were recorded daily and their composition analyzed regarding fat, protein and fatty acids content. The economic viability was carried out by considering the prices of the feedstuffs fed and the daily consumption in the diet for each treatment. The economic benefit was obtained by the difference between the receipt with the milk sale and the cost with the feeding of the animals. The pay for quality was estimated on the basis of the mean of eight systems utilized by businesses in the dairy branch on the basis of the fat and protein contents and by milk volume. The diet without the addition of SO was the one which provided the greatest economic benefit. The addition of SO in the sugar-cane based diets was not economically viable due to the additional expenditures with SO and the penalizations resulting from the reduction of the milk protein and fat content.(AU)

Viabilidade econômica da inclusão de óleo de girassol em dieta à base de cana-de-açúcar para vacas em lactação / Economic viability of feeding different levels of sunflower oil in sugarcane-based diets to lactating cows

Objetivou-se avaliar a viabilidade econômica da produção de leite de vacas Holandês x Gir, pela inclusão de níveis crescentes de óleo de girassol (0,0; 1,5; 3,0 e 4,5 por cento) na matéria seca de dietas baseadas em cana-de-açúcar. Os dados utilizados no estudo foram obtidos de experimento realizado com 12 vacas Holandês x Gir, multíparas, com produção média de 18,2kg/dia de leite, distribuídas em três quadrados latinos 4 x 4, conforme a produção de leite, a ordem de lactação e o peso corpóreo. As dietas foram isoproteicas, fornecidas ad libitum na forma de mistura total (relação volumoso:concentrado de 60:40, base matéria seca), e os consumos das vacas determinados diariamente. As produções individuais diárias de leite foram registradas, e sua composição foi analisada quanto aos teores de gordura, proteína e ácidos graxos. A viabilidade econômica foi realizada considerando-se os preços dos ingredientes fornecidos e o consumo diário da dieta de cada tratamento. O benefício econômico foi obtido pela diferença entre a receita, com a venda do leite, e o custo com alimentação dos animais. O pagamento por qualidade foi estimado pela média de oito sistemas utilizados por empresas do ramo de laticínios, com base nos teores de gordura, proteína e no volume de leite. A dieta sem inclusão de OG foi a que proporcionou maior benefício econômico. A inclusão de OG nas dietas baseadas em cana-de-açúcar não foi viável, economicamente, devido aos gastos adicionais com OG e às penalizações resultantes da redução dos teores de proteína e de gordura do leite...

The aim of this study was to evaluate the economic viability of the milk yield of Holstein x Gir cows by the addition of growing levels of sunflower oil (SO) (0.0, 1.5, 3.0 and 4.5 percent) in the dry matter of sugar-cane based diets. The data utilized in the study were obtained from an experiment conducted with 12 multiparous Holstein x Gir cows, with average yield of 18.2kg/day of milk, distributed into three 4 x 4 Latin squares according to milk yield, lactation order and body weight. The diets were isoprotein, a total mixture fed at libitum (ratio roughage concentrate of 60:40, dry matter basis) and cow consumption was determined daily. The individual milk yields were recorded daily and their composition analyzed regarding fat, protein and fatty acids content. The economic viability was carried out by considering the prices of the feedstuffs fed and the daily consumption in the diet for each treatment. The economic benefit was obtained by the difference between the receipt with the milk sale and the cost with the feeding of the animals. The pay for quality was estimated on the basis of the mean of eight systems utilized by businesses in the dairy branch on the basis of the fat and protein contents and by milk volume. The diet without the addition of SO was the one which provided the greatest economic benefit. The addition of SO in the sugar-cane based diets was not economically viable due to the additional expenditures with SO and the penalizations resulting from the reduction of the milk protein and fat content...

Qualidade nutricional e estabilidade oxidativa de manteigas produzidas do leite de vacas alimentadas com cana-de-açúcar suplementada com óleo de girassol / Nutritional quality and oxidative stability of butter obtained from cows fed sugar-cane supplemented with sunflower oil

O objetivo deste estudo foi avaliar o perfil de ácidos graxos (AG), os índices de qualidade nutricional e a estabilidade oxidativa (EO) de manteigas produzidas do leite de vacas alimentadas com dietas à base de cana-de-açúcar contendo níveis crescentes de óleo de girassol (OG): 0 (controle); 1,5; 3,0 e 4,5% da matéria seca (MS). O perfil de AG das manteigas foi analisado por cromatografia gasosa, e a EO foi determinada utilizando-se o equipamento Rancimat®, modelo 743, operado a 120ºC e fluxo de ar de 20L/h. As concentrações dos AG rumênico (CLA cis-9, trans-11), vacênico (C18:1 trans-11) e oleico (C18:1 cis-9) na gordura das manteigas foram aumentadas em 867, 687 e 148%, respectivamente, à medida que se aumentou de 0 para 4,5% o nível de OG na dieta. Por outro lado, as concentrações dos AG saturados de cadeia média foram linearmente reduzidas (P<0,0001) na gordura das manteigas, em razão do incremento de OG nas dietas. Quanto aos índices de qualidade nutricional, houve redução linear (P<0,0001) no índice de aterogenicidade e no de trombogenicidade e aumento da relação entre AG hipo e hipercolesterolêmicos, em resposta ao aumento do nível de OG na dieta. Consistente com o incremento (P<0,0001) nas concentrações totais dos AG mono e poli-insaturados, a EO da gordura das manteigas foi linearmente reduzida (P<0,0001) em razão do incremento de OG nas dietas. Concluiu-se que a suplementação com OG melhorou a qualidade nutricional das manteigas produzidas do leite de vacas Holandês x Gir devido a mudanças positivas no perfil de AG da gordura. Entretanto, tais mudanças na composição dos AG da gordura foram acompanhadas de redução da EO das manteigas, associada à menor vida de prateleira.(AU)

The objective of this study was to evaluate the fatty acid (FA) profile, nutritional quality and oxidative stability (OE) indexes of butter obtained from milk of cows fed sugar cane-based diets containing increasing levels of sunflower oil (SO): 0 (Control); 1.5; 3.0 and 4.5% of diet DM. The butter FA profile was analyzed by gas chromatography and OE was determined using the Rancimat® equipment (model 743) operated at 120ºC and air flow of 20 L/h. The concentrations of rumenic acid (cis-9 trans-11 CLA), vaccenic acid (trans-11 C18:1) and oleic acid (cis-9 C18:1) in butter fat were increased by 867, 687 and 148%, respectively, as the dietary SO level increased from 0 to 4.5%. In contrast, the concentrations of medium chain saturated FA were linearly reduced (P<0.05) in butter fat from cows fed increasing levels of SO. Regarding the butter nutritional quality, a linear decrease (P<0.0001) in atherogenicity and thrombogenicity indexes and a linear increase (P<0.0001) in the hypocholesterolemic/ hypercholesterolemic ratio were observed compared to control, 1.5, 3.0 and 4.5% SO, respectively. Consistent with the increased (P<0.0001) concentration of mono and polyunsaturated FA, the OE of butter fat was linearly reduced (P<0.0001) as the dietary SO level increased. It was concluded that diet supplementation with SO improved the nutritional quality of butter fat of Holstein x Gir dairy cows as a result of positive changes in milk FA profile. However, these changes in milk FA composition were accompanied by a reduction in the SO of butter, which in turn is associated with a shorter shelf life.(AU)

Qualidade nutricional e estabilidade oxidativa de manteigas produzidas do leite de vacas alimentadas com cana-de-açúcar suplementada com óleo de girassol / Nutritional quality and oxidative stability of butter obtained from cows fed sugar-cane supplemented with sunflower oil

O objetivo deste estudo foi avaliar o perfil de ácidos graxos (AG), os índices de qualidade nutricional e a estabilidade oxidativa (EO) de manteigas produzidas do leite de vacas alimentadas com dietas à base de cana-de-açúcar contendo níveis crescentes de óleo de girassol (OG): 0 (controle); 1,5; 3,0 e 4,5% da matéria seca (MS). O perfil de AG das manteigas foi analisado por cromatografia gasosa, e a EO foi determinada utilizando-se o equipamento Rancimat®, modelo 743, operado a 120ºC e fluxo de ar de 20L/h. As concentrações dos AG rumênico (CLA cis-9, trans-11), vacênico (C18:1 trans-11) e oleico (C18:1 cis-9) na gordura das manteigas foram aumentadas em 867, 687 e 148%, respectivamente, à medida que se aumentou de 0 para 4,5% o nível de OG na dieta. Por outro lado, as concentrações dos AG saturados de cadeia média foram linearmente reduzidas (P<0,0001) na gordura das manteigas, em razão do incremento de OG nas dietas. Quanto aos índices de qualidade nutricional, houve redução linear (P<0,0001) no índice de aterogenicidade e no de trombogenicidade e aumento da relação entre AG hipo e hipercolesterolêmicos, em resposta ao aumento do nível de OG na dieta. Consistente com o incremento (P<0,0001) nas concentrações totais dos AG mono e poli-insaturados, a EO da gordura das manteigas foi linearmente reduzida (P<0,0001) em razão do incremento de OG nas dietas. Concluiu-se que a suplementação com OG melhorou a qualidade nutricional das manteigas produzidas do leite de vacas Holandês x Gir devido a mudanças positivas no perfil de AG da gordura. Entretanto, tais mudanças na composição dos AG da gordura foram acompanhadas de redução da EO das manteigas, associada à menor vida de prateleira.

The objective of this study was to evaluate the fatty acid (FA) profile, nutritional quality and oxidative stability (OE) indexes of butter obtained from milk of cows fed sugar cane-based diets containing increasing levels of sunflower oil (SO): 0 (Control); 1.5; 3.0 and 4.5% of diet DM. The butter FA profile was analyzed by gas chromatography and OE was determined using the Rancimat® equipment (model 743) operated at 120ºC and air flow of 20 L/h. The concentrations of rumenic acid (cis-9 trans-11 CLA), vaccenic acid (trans-11 C18:1) and oleic acid (cis-9 C18:1) in butter fat were increased by 867, 687 and 148%, respectively, as the dietary SO level increased from 0 to 4.5%. In contrast, the concentrations of medium chain saturated FA were linearly reduced (P<0.05) in butter fat from cows fed increasing levels of SO. Regarding the butter nutritional quality, a linear decrease (P<0.0001) in atherogenicity and thrombogenicity indexes and a linear increase (P<0.0001) in the hypocholesterolemic/ hypercholesterolemic ratio were observed compared to control, 1.5, 3.0 and 4.5% SO, respectively. Consistent with the increased (P<0.0001) concentration of mono and polyunsaturated FA, the OE of butter fat was linearly reduced (P<0.0001) as the dietary SO level increased. It was concluded that diet supplementation with SO improved the nutritional quality of butter fat of Holstein x Gir dairy cows as a result of positive changes in milk FA profile. However, these changes in milk FA composition were accompanied by a reduction in the SO of butter, which in turn is associated with a shorter shelf life.

Thermal entanglement in an orthogonal dimer-plaquette chain with alternating Ising-Heisenberg coupling.

In this paper we explore the entanglement in an orthogonal dimer-plaquette Ising-Heisenberg chain, assembled between plaquette edges, also known as orthogonal dimer plaquettes. The quantum entanglement properties involving an infinite chain structure are quite important, not only because the mathematical calculation is cumbersome but also because real materials are well represented by infinite chains. Using the local gauge symmetry of this model, we are able to map onto a simple spin-1 like Ising and spin-1/2 Heisenberg dimer model with single effective ion anisotropy. Thereafter this model can be solved using the decoration transformation and transfer matrix approach. First, we discuss the phase diagram at zero temperature of this model, where we find five ground states, one ferromagnetic, one antiferromagnetic, one triplet-triplet disordered and one triplet-singlet disordered phase, beside a dimer ferromagnetic-antiferromagnetic phase. In addition, we discuss the thermodynamic properties such as entropy, where we display the residual entropy. Furthermore, using the nearest site correlation function it is possible also to analyze the pairwise thermal entanglement for both orthogonal dimers. Additionally, we discuss the threshold temperature of the entangled region as a function of Hamiltonian parameters. We find a quite interesting thin reentrance threshold temperature for one of the dimers, and we also discuss the differences and similarities for both dimers.

Influence of pretreatment of cotton yarns prior to biopolishing.

Cellulase is one of the enzymes most commonly used in the textile industry for the biopolishing process. The appropriate choice of pretreatment is a possible route to promoting enzymatic attack in situations in which this is not favored due to the effects of packing. In order to evaluate the influence of pretreatment the yarn was maintained in water for 24h before biopolishing to promote greater spacing between the chains. In the tensile testing the pretreated Combed 13/1 yarn showed a greater percentage reduction in the maximum breaking force following biopolishing, evidencing a stronger enzymatic attack. Also, the Combed 13/1 and OE 14/1 yarns without pretreatment had an approximately 22% reduction in the shrinkage and after pretreatment the Carded 13/1 yarn had the best shrinkage reduction values (18%). These data demonstrate that the introduction of the pretreatment promotes a change in the access of the enzyme to the fiber.

Frustrated Ising model on the Cairo pentagonal lattice.

Through the direct decoration transformation approach, we obtain a general solution for the pentagonal Ising model, showing its equivalence to the isotropic free-fermion eight-vertex model. We study the ground-state phase diagram, in which one ferromagnetic (FM) state, one ferrimagnetic (FIM) state, and one frustrated state are found. Using the exact solution of the pentagonal Ising model, we discuss the finite-temperature phase diagrams and find a phase transition between the FIM state and the disordered state as well as a phase transition between the disordered state and the FM state. We also discuss some additional remarkable properties of the model, such as the magnetization, entropy, and specific heat, at finite temperature and at its low-temperature asymptotic limit. Because of the influence of the second-order phase transition between the frustrated and ferromagnetic phases, we obtain surprisingly low values of the entropy and the specific heat until the critical temperature is reached.

The mystery of the 'resin-of-canuaru': a medicine used by caboclos river-dwellers of the Amazon, Amazonas, Brazil.

ETHNOPHARMACOLOGICAL RELEVANCE: 'Resin-of-canuaru' is a medicine utilized by caboclos living in the Amazon Region, Brazil. There is a mystery regarding its origin because the caboclos maintain that this substance is derived only from animal secretions (from a frog called canuaru), whereas the historic literature claims that 'resin-of-canuaru' is derived solely from a plant exudate (resin). Based on our ethnographic studies, we hypothesized that this substance is a combination of both. Because the past reports on this resiniferous material in the literature are based solely on observations, we aimed to present ethnographic, zoological and chemical data to try to elucidate the origin of the 'resin-of-canuaru'. MATERIALS AND METHODS: Ethnographic techniques and methods were applied, including participant observation, the use of field diaries and informal and unstructured interviews. The canuaru frog (Trachycephalus resinifictrix Goeldi, 1907) and 'resin-of-canuaru' were collected for taxonomic identification and chemical analysis, respectively. The resiniferous 'resin-of-canuaru' was extracted using MeOH and then analyzed by silica gel TLC and NMR. RESULTS: Canuaru frogs live in tree cavities and secrete a large amount of substances during spawning, resulting in a resiniferous material. NMR analysis of the MeOH extract of this crude material showed peaks assigned to 3,4-secofriedel-4(23)-en-3-oic acid (putranjuvic acid) and its methyl ester derivative (methyl putranjivate) and to biogenetic precursor of these two compounds (a lactone derivative), which is formed by the oxidation of friedelin. Based on evidence that Protium species accumulate primarily tetracyclic/pentacyclic triterpenoids and that the co-occurrence of the compounds listed above is rarely described in plant species, we suggest that these compounds could be products of the biotransformation of friedelin by the frog. CONCLUSIONS: According to our data, the 'resin-of-canuaru' seems to have both animal and vegetal origins.

Geometrical frustration of an extended Hubbard diamond chain in the quasiatomic limit.

We study the geometrical frustration of an extended Hubbard model on a diamond chain, where vertical lines correspond to the hopping and repulsive Coulomb interaction terms between sites while the remaining lines represent only the Coulomb repulsion term. The phase diagrams at zero temperature show quite curious phases: five types of frustrated states and four types of nonfrustrated states, ordered antiferromagnetically. Although a decoration transformation was derived for spin-coupling systems, this approach can be applied to electron-coupling systems. Thus the extended Hubbard model can be mapped onto another effective extended Hubbard model in the atomic limit with additional three- and four-body couplings. This effective model is solved exactly using the transfer-matrix method. In addition, using the exact solution of this model, we discuss several thermodynamic properties away from the half-filled band, such as chemical potential behavior, electronic density, and entropy, for which we study geometrical frustration. Consequently, we investigate the specific heat as well.

Two-dimensional XXZ -Ising model on a square-hexagon lattice.

We study a two-dimensional XXZ -Ising model on a square-hexagon (denoted for simplicity by 4-6) lattice with spin 1/2. The phase diagram at zero temperature is discussed, where five states are found, two types of ferrimagnetic states, two types of antiferromagnetic states, and one ferromagnetic state. To solve this model, we have mapped onto the eight-vertex model with union Jack interaction term, and it was verified that the model cannot be completely mapped onto eight-vertex model. However, by imposing an exact solution condition, we have found the region where the XXZ -Ising model on 4-6 lattice is exactly soluble with one free parameter, particularly for the case of symmetric eight-vertex model condition. In this manner we have explored the properties of the system and have analyzed the interacting competition parameters which preserve the region where there is an exact solution. Unfortunately the present model does not satisfy the free fermion condition of the eight-vertex model, unless for a trivial solution. Even so, we are able to discuss the critical point region, beyond the region of exact resolvability.

Thermodynamics of the Mn(12)-ac molecule in a skew magnetic field at [Formula: see text] K.

We derive the high-temperature expansion of the Helmholtz free energy of the quantum and classical models for the Mn(12)-ac molecule in the presence of a skew magnetic field, including the transverse term in the Hamiltonians, for [Formula: see text] K. In this region of temperature, we show that the transverse term can give a measurable contribution to the x component of the magnetization. We obtain the specific heat per site of a powder sample of Mn(12)-ac under a constant magnetic field. For strong skew magnetic fields (h/D>1), the specific heat differs up to 20% from its value of a crystal sample under purely longitudinal magnetic fields. Finally, we obtain that in the limit [Formula: see text], the values of the classical and quantum specific heat differ; in particular, for [Formula: see text] this difference is 0.96%.