Variation of compression and tensile properties of cork

Comunicação oral da qual só está disponível o resumo.The compression and tensile properties of cork were studied on samples obtained from cork planks with densities ranging 0.12 - 0.20 g.cm-3 and porosities 0.5 to 22.0%, and different commercial quality classes. The stress-strain curves in compression were characterized by an elastic region up to approximately 5% strain, followed by a large plateau for strains up to 60% caused by the progressive buckling of cell walls, with a steep increase of stress for higher strains corresponding to cell collapse and densification. The direction of compression was a highly significant factor of variation, with cork showing higher strength for the radial compression. The stress-strain curves were also very similar regardless of the porosity of the samples. The tensile properties of cork were measured in three radial positions in the cork planks: the inner side (belly side), the outer site (back side) and a mid position. The results showed that the distance to the inner part plank in tensile tests was a highly significant factor of variation. The Young moduli measured by a tensile stress were significantly higher near the inner part of the plank and lower in the outer part. The compression and tensile properties of cork samples obtained from cork planks of different quality classes did not differ significantly. An exponential model of Young’s modulus in function of cork density and porosity could be adjusted for the compression and tensile behaviour of cork. The large variability observed is strongly influenced by the structural features involving the lenticular channels walls, namely the presence of thick walled and lignified cells

Relation between mechanical properties of cork from Quercus suber

Cork is known as the material used for the production of wine stoppers. The specific properties of cork, e.g. low density, very low permeability to water, elastic properties and inertness have made it the best sealant for quality wine. Here we studied the relation between compression, tensile and bending stress in cork and the influence of structural characteristics of cork on its mechanical behaviour. The material was sampled from raw cork planks of good quality (class 1) and poor quality (class 4) collected at one industrial mill after post-harvest six-month air stabilization, water boiling and air drying as usually applied in cork industrial processing. The samples had densities ranging 0.123 - 0.203 g.cm-3 and porosities between 0.5 and 22.0%. There are differences between the type of stress and the corresponding direction of stress. For the same direction of stress, the Young modulus in tension is higher then in bending and it is lowest in compression. The bending Young modulii were well correlated with the tensile Young modulii, because while in bending the sample is submitted to both tensile and compression stresses, the fracture occurs in the tensile zone. There were no significant differences in the mechanical properties of cork samples obtained from cork planks of different quality classes but the density is an important factor and samples with higher density showed overall larger resistance. Mechanical properties were influenced by the structural features related to the lenticular channels, namely the presence of thick walled and lignified cells that may border the lenticular channels

Metal contaminants in Largemouth bass (Micropterus salmoides) collected in large dams from Tejo River basin and small irrigation dams

Largemouth bass (Micropterus salmoides) is a very important fresh water fish in the Portuguese regional cuisine mainly in the countryside (Central region and north Alentejo). Because there’s no aquaculture industry, all eaten largemouth bass in Portugal are collected in large dams (Basins of Tejo and Guadiana rivers) and small irrigation dams. For decades, the Tejo River received environmental pollutants from non-point and point sources that included intensive agriculture, industrial entities, municipalities and nuclear power plant. The aim of this work was to evaluate some metals (Cd, Cr, Cu, Fe, Hg, Mn, Pb, Zn) present on largemouth bass muscle tissue collected in the section of Tejo River that makes border between Portugal and Spain (TR) (N=9) and collected in three irrigation reservoirs (IR) located near Castelo Branco – Portugal (N=11). Individual were weighted and measured. Age was determined by examining fish scales, and sex determined by gonads observation. Samples for liver, dorsolateral muscle and tail muscle were collected from the right side of the fish. TR average weight 435.14g (±109.15), average length 278.33mm (±23.28), average K condition factor 1.98 (±0.09) and average age 3.11 years (±0,78) were similar (P>0.05) to IR average weight 410.84g (±137.71), average length 278.36mm (±31.13), average K condition factor 1.86 (±0.17) and average age 3.18 years (±0,60). Total mercury was determined in freeze-dried samples by atomic absorption spectrometry with thermal decomposition and gold amalgamation. For the other metal analysis, freeze-dried powders were mineralized with a mixture of HNO3 and H2O2, followed by ICP-OES quantification. Cd and Pb presented concentrations below LOQ (0.025 and 0.15mg.kg-1wet.weight, respectively) for all muscle samples. These values are below legal limits in EU (0.05 and 0.3mg.kg-1wet.weight, respectively). Average Hg levels are below legal limits (0.5mg.kg-1wet.weight) and muscle presented higher levels than liver. These contaminant levels indicate that are no contamination sources in the sampling sites. Cu, Cr, Fe, Mn and Zn are essential micronutrients. Their concentrations were not significantly different between dorsal and tail muscle and were higher in liver (P>0.05), with mean concentrations on muscle being, respectively: TR 0.16 (±0.07), <LOQ(0.03), 1.45 (±0.42), 0.04 (±0.04) and 3.76 (±0.39) mg.kg-1wet.weight; IR 0.16 (±0.02), <LOQ(0.03), 1.80 (±0.52), 0.05 (±0.05) and 4.17 (±0.56) mg.kg-1wet.weight. We concluded that metallic concentrations of largemouth bass muscle tissues were below the maximum permissible for a safety utilization of theses fishes in human nutrition

Characterisation of yeast flora isolated from an artisanal Portuguese ewe's cheese

www.elsevier.nl/locate/ijfoodmicroThe evolution of the yeast flora was studied for an artisanal semi-hard ewes’ cheese made from raw milk. Mean log10 22 yeast counts per gram of cheese body ranged from 2.7 to 6.4, with the higher counts observed after a ripening period of 30 23 days. The yeast population decreased thereafter and, at the end of curing process, reached values similar to those of the 24 beginning. A total of 344 yeasts strains were randomly isolated from the curd and cheese body during the 60 days long 25 ripening period. Esterase activity was common to almost all isolates (98%) while proteolysis was observed in 12% of the 26 total yeast population. The proportion of strains with positive glucose fermentation increased from 21% in the curd to 75% at 27 the end of the ripening period. A total of 150 isolates representative of the physiological characteristics tested were examined 28 with the API ID 32C system showing different degrees of quality of identification. Only 15% of the strains (23 isolates) were 29 excellently identified being assigned to the species Candida zeylanoides. The most frequent species appeared to be 30 Debaryomyces hansenii (anamorph Candida famata) and Candida intermedia. These two species amounted to 9% of the 31 yeasts in the curd increasing to 86% at the end of the ripening period

Vortex behavior near a spin vacancy in 2D XY-magnets

The dynamical behavior of anisotropic two dimensional Heisenberg models is still a matter of controversy. The existence of a central peak at all temperatures and a rich structure of magnon peaks are not yet understood. It seems that the central peaks are related, in some way, to structures like vortices. In order to contribute to the discussion of the dynamical behavior of the model we use Monte Carlo and spin dynamics simulations as well analytical calculations to study the behavior of vortices in the presence of nonmagnetic impurities. Our simulations show that vortices are attracted and trapped by the impurities. Using this result we show that if we suppose that vortices are not very much disturbed by the presence of the impurities, then they work as an attractive potential to the vortices explaining the observed behavior in our simulations.Comment: 4 pages, 6 figure

Correlação entre o conteúdo inorgânico e a polimerização da matriz orgânica das resinas compostas para restaurações dentárias: uma revisão narrativa

Introduction: In recent years, resin-matrix composite materials have revealed a fast technological improvement for dental applications. However, there are still some drawbacks related to the chemical composition, polymerization, and mechanical properties of resin-matrix composites with consequences in long-term clinical success. Objective: This study aimed to perform a narrative review regarding the effects of inorganic fillers on the organic matrix polymerization of resin-matrix composites. Materials and Methods: A search was performed in PubMed using relevant related key terms related to the chemical composition, properties and polymerization of resin matrix composites. Relevant studies published between 2001 and 2021 were selected. Results: The studies included in the present research provided relevant information on the chemical composition and properties of resin composites and polymerization factors, including the time, wavelength mode, and equipment. Studies have reported that silica and silicate nano-scale particles improve light transmission through resin-matrix composites and the degree of conversion of monomers in the organic matrix. Micrometric particles with a high refractive index can decrease the degree of conversion of monomers in the organic matrix. Conclusion: The polymerization of resin-matrix composites is affected by light scattering due to the type of inorganic particles and the differences in refractive indexes of inorganic and organic contents.Introdução: Nos últimos anos, as resinas compostas têm sido melhoradas em termos tecnológicos, permitindo o alcance de melhores prognósticos na medicina dentária. Entretanto, subsistem algumas limitações relacionadas com a composição química e as propriedades das resinas compostas com consequências no sucesso clínico a longo prazo. Objetivo: O objetivo deste trabalho foi realizar uma revisão narrativa sobre a influência da componente inorgânica na polimerização da matriz orgânica das resinas compostas usadas para restauração dentária. Materiais e Métodos: A pesquisa foi realizada na plataforma PubMed utilizando termos de pesquisa relacionados com a composição química, propriedades e a polimerização das resinas compostas, para seleção de artigos relevantes ao tema. Resultados: Os estudos identificados reportam diferentes fatores relacionados com a polimerização incluindo modo, tempo, equipamento e a composição química das resinas compostas. Os estudos indicam que partículas nanométricas à base de sílica ou silicatos promovem uma maior transmissão de luz à matriz orgânica o que favorece a polimerização do material. Por outro lado, partículas micrométricas com um alto índice de refração podem diminuir o grau de conversão dos monómeros da matriz orgânica. Conclusão: A polimerização das resinas compostas é afetada pela dispersão da luz, devido ao tamanho das partículas inorgânicas e aos índices de refração da componente orgânica e inorgânica. De fato, um maior controlo da composição química e do tamanho de partículas inorgânicas aumenta o grau de polimerização das resinas compostas

Ionization degree of the electron-hole plasma in semiconductor quantum wells

The degree of ionization of a nondegenerate two-dimensional electron-hole plasma is calculated using the modified law of mass action, which takes into account all bound and unbound states in a screened Coulomb potential. Application of the variable phase method to this potential allows us to treat scattering and bound states on the same footing. Inclusion of the scattering states leads to a strong deviation from the standard law of mass action. A qualitative difference between mid- and wide-gap semiconductors is demonstrated. For wide-gap semiconductors at room temperature, when the bare exciton binding energy is of the order of T, the equilibrium consists of an almost equal mixture of correlated electron-hole pairs and uncorrelated free carriers.Comment: 22 pages, 6 figure

Critical Collapse of Cylindrically Symmetric Scalar Field in Four-Dimensional Einstein's Theory of Gravity

Four-dimensional cylindrically symmetric spacetimes with homothetic self-similarity are studied in the context of Einstein's Theory of Gravity, and a class of exact solutions to the Einstein-massless scalar field equations is found. Their local and global properties are investigated and found that they represent gravitational collapse of a massless scalar field. In some cases the collapse forms black holes with cylindrical symmetry, while in the other cases it does not. The linear perturbations of these solutions are also studied and given in closed form. From the spectra of the unstable eigen-modes, it is found that there exists one solution that has precisely one unstable mode, which may represent a critical solution, sitting on a boundary that separates two different basins of attraction in the phase space.Comment: Some typos are corrected. The final version to appear in Phys. Rev.

Incidência do míldio em cebola sob adubação mineral e orgânica.

Analisou-se a relação entre adubação mineral e orgânica sobre a incidência de míldio (Peronospora destructor) em cebola (Allium cepa). O trabalho constituiu-se de dois experimentos localizados em Ituporanga, conduzidos entre agosto e dezembro de 1998. O experimento 1, com fontes orgânicas, constou dos tratamentos: esterco de suínos, esterco de aves, composto, esterco de peru e húmus, na dosagem de 75 kg/ha de N; esterco de suínos, na dosagem de 37,5 kg/ha de N; adubação mineral, 30-120-60 kg/ha de N-P2O5-K2O; 60-240-120 kg/ha de N-P2O5-K2O e testemunha sem adubação. O experimento 2 constou dos tratamentos: fontes minerais, 30-120-60 kg/ha de N-P2O5-K2O; 90-360-180 kg/ha de N-P2O5-K2O; 75 kg/ha de N; 225 kg/ha de N; 80 kg/ha de P2O5; 240 kg/ha de P2O5; 60 kg/ha de K2O; 180 kg/ha de K2O; esterco de suínos + fosfato natural, em três combinações, 7,9+0,1, 15,7+0,2 e 47,2+0,6 t/ha, respectivamente; testemunha sem adubação. Não houve diferença entre as fontes mineral e orgânica sobre a incidência de míldio. A relação entre nutrientes e doença foi variável entre datas de amostragem e distinta para fontes minerais e orgânicas

Lateral gene transfer generates accessory genes that accumulate at different rates within a grass lineage

Summary Lateral gene transfer (LGT) is the movement of DNA between organisms without sexual reproduction. The acquired genes represent genetic novelties that have independently evolved in the donor's genome. Phylogenetic methods have shown that LGT is widespread across the entire grass family, although we know little about the underlying dynamics. We identify laterally acquired genes in five de novo reference genomes from the same grass genus (four Alloteropsis semialata and one Alloteropsis angusta). Using additional resequencing data for a further 40 Alloteropsis individuals, we place the acquisition of each gene onto a phylogeny using stochastic character mapping, and then infer rates of gains and losses. We detect 168 laterally acquired genes in the five reference genomes (32–100 per genome). Exponential decay models indicate that the rate of LGT acquisitions (6–28 per Ma) and subsequent losses (11–24% per Ma) varied significantly among lineages. Laterally acquired genes were lost at a higher rate than vertically inherited loci (0.02–0.8% per Ma). This high turnover creates intraspecific gene content variation, with a preponderance of them occurring as accessory genes in the Alloteropsis pangenome. This rapid turnover generates standing variation that can ultimately fuel local adaptation