Numerical evaluation of the modulus of longitudinal elasticity in structural round timber elements of the Eucalyptus genus

Currently, the standards that deal with the determination of the properties of rigidity and strength for structural round timber elements do not take in consideration in their calculations and mathematical models the influence of the existing irregularities in the geometry of these elements. This study has as objective to determine the effective value of the modulus of longitudinal elasticity for structural round timber pieces of the Eucalyptus citriodora genus by a technique of optimization allied to the Inverse Analysis Method, to the Finite Element Method and the Least Square Method.

The position effect of structural Eucalyptus round timber on the flexural modulus of elasticity

Round timber has great use in civil construction, performing the function of beams, columns, foundations, poles for power distribution among others, with the advantage of not being processed, such as lumber. The structural design of round timber requires determining the elastic properties, mainly the modulus of elasticity. The Brazilian standards responsible for the stiffness and strength determination of round timber are in effect for over twenty years with no technical review. Round timber, for generally present an axis with non-zero curvature according to the position of the element in the bending test, may exhibit different values of modulus of elasticity. This study aims to analyze the position effect of Eucalyptus grandis round timber on the flexural modulus of elasticity. The three-point bending test was evaluated in two different positions based on the longitudinal rotation of the round timber element. The results revealed that at least two different positions of the round timber element are desired to obtain significant modulus of elasticity.

Alternative methodology for calculating the modulus of elasticity of wooden beams of structural dimensions

This study aims to present an alternative calculation methodology based on the Least Squares Method for determining the modulus of elasticity in bending wooden beams of structural dimensions. The equations developed require knowledge of three or five points measured in displacements along the piece, allowing greater reliability on the response variable, using the statistical bending test at three points and non-destructively, resulting from imposition of measures from small displacements L/300 and L/200, the largest being stipulated by the Brazilian norm NBR 7190:1997. The woods tested were Angico, Cumaru, Garapa and Jatoba. Besides obtaining the modulus of elasticity through the alternative methodology proposed, these were also obtained employing the Brazilian norm NBR 7190:1997, adapted to the condition of non-destructive testing (small displacements) and for pieces of structural dimensions. The results of the modulus of elasticity of the four species of wood according to both calculation approaches used proved to be equivalent, implying the good approximation provided by the methodology of calculation adapted from the Brazilian norm.

Determining the concrete stiffness matrix through ultrasonic testing

The determination of the modulus tangent (Eci ) and of the modulus secant (Ecs) of the concrete can be done using compression test but, to be simpler, it is used relations with characteristic strength (f ck). Relations are also used to determine the transversal modulus (Gc) and, in the case of the Poisson's ratio (ν), a fixed value 0.20 is established. The objective of this research was to evaluate the use of the ultrasonic propagation waves to determine these properties. For the tests were used specimens with f ck varying from 10 to 35 MPa. For the ultrasonic tests were used cylindrical and cubic specimens. The modulus of deformation obtained by ultrasound was statistically equivalent to the obtained by compression tests. The results of modules obtained using the relations with f ck was far away from those obtained by ultrasound or by compression tests. The Poisson's ratio obtained by ultrasound was superior to the fixed value. We can conclude that the concrete characterization by ultrasound is consistent and, to this characterization the cylindrical specimen, normally used to determine f ck, can be used.

Relationships and estimates of longitudinal growth stress in Eucalyptus dunnii at different ages

The objective of this study was to obtain estimates of longitudinal growth stresses in standing trees of the Eucalyptus dunnii Maiden at eight, thirteen, fifteen and nineteen years of age and to determine their relationships with wood characteristics. The longitudinal growth stresses were indirectly measured by the "CIRAD-Forêt" method and estimated from both the dynamic modulus of elasticity and the modulus of elasticity in tension parallel to the grain. The longitudinal residual strain (LRS) and the estimates of the longitudinal growth stresses tended to increase with the age of the material. The LRS correlated positively and significantly with all the growth stresses estimates. The largestes magnitudes were at 13, 15 and 19 years of age. The basic density presented high, positive and significant correlations with the dynamic modulus of elasticity, estimated in the longitudinal direction, for wood saturated and at 12% moisture content, for all the ages assessed. All the growth stresses estimates presented high, positive and significant correlations between themselves.

Comparison of the quantification of caffeine in human plasma by gas chromatography and ELISA

In the present study we evaluated the precision of the ELISA method to quantify caffeine in human plasma and compared the results with those obtained by gas chromatography. A total of 58 samples were analyzed by gas chromatography using a nitrogen-phosphorus detector and routine techniques. For the ELISA test, the samples were diluted to obtain a concentration corresponding to 50% of the absorbance of the standard curve. To determine whether the proximity between the I50 of the standard curve and that of the sample would bring about a more precise result, the samples were divided into three blocks according to the criterion of difference, in modulus, of the I50 of the standard curve and of the I50 of the sample. The samples were classified into three groups. The first was composed of 20 samples with I50 up to 1.5 ng/ml, the second consisted of 21 samples with I50 ranging from 1.51 to 3 ng/ml, and the third of 17 samples with I50 ranging from 3.01 to 13 ng/ml. The determination coefficient (R² = 0.999) showed that the data obtained by gas chromatography represented a reliable basis. The results obtained by ELISA were also reliable, with an estimated Pearson correlation coefficient of 0.82 between the two methods. This coefficient for the different groups (0.88, 0.79 and 0.49 for groups 1, 2 and 3, respectively) showed greater reliability for the test with dilutions closer to I50.

Effect of addition of different hydrocolloids on pasting, thermal, and rheological properties of cassava starch

Starches and gums are hydrocolloids frequently used in food systems to provide proper texture, moisture, and water mobility. Starch-gum interaction in food systems can change the starch granule swelling and its gelatinization and rheological properties. In this study, the effect of the addition of xanthan gum (XG), sodium carboxymethyl cellulose (SCMC), and carrageenan (CAR) at the concentrations of the 0.15, 0.25, 0.35 and 0.45% (w/v) on the pasting, thermal, and rheological properties of cassava starch was studied. The swelling power (SP) and the scanning electron microscopy (SEM) of the starch gels were also evaluated. The results obtained showed that xanthan gum (XG) had a strong interaction with the cassava starch penetrating between starch granules causing increase in pasting viscosities, SP, storage and loss (G', and G", respectively) modulus and reduction in the setback of the starch; sodium carboxymethyl cellulose (SCMC) greatly increased the pasting viscosities, the SP, and the storage and loss (G', and G", respectively) modulus of the starch-mixtures, mainly due to its greater capacity to hold water and not due to the interaction with cassava starch. Carrageenan (CAR) did not change any of the starch properties since there was no interaction between this gum and cassava starch at the concentrations used.

Efectos del herbicida Paraquat sobre el zooplancton

The effects of 0.1; 0.2; 0.4 and 0.8 mlPQ/L were analized on a zooplankton community, to determine the most sensitive species and to analize the occurence of physical abnormalities. A total of 40 taxa were determined. Paraquat affected significantly the zooplankton density but not the species richness. A progressive state of deformation of these organisms was also observed. Paraquat showed to be highly toxic for the zooplankton, so this herbicide should be strictly regulated in aquatic and terrestrial ecosystems.

Resistência mecânica de hidrogéis termo-sensíveis constituídos de Alginato-Ca2+ / PNIPAAm, tipo Semi-IPN

Thermosensitive hydrogels were synthesized using alginate-Ca2+ in association with a thermosensitive polymer, such as PNIPAAm. The mechanical properties of the hydrogels were determined measuring the maximum tension of deformation. With the increase of the temperature by 25 to 40 ºC above the LCST the chains of PNIPAAm collapsed, dragging the alginate net and diminishing the size of the pores. The decrease in the size of the pores of the hydrogel was followed by an increase in the mechanicals resistance of the material.

Theoretical investigations of the bulk modulus in the tetra-cubic transition of PbTiO3 material

Resulting from ion displacement in a solid under pressure, piezoelectricity is an electrical polarization that can be observed in perovskite-type electronic ceramics, such as PbTiO3, which present cubic and tetragonal symmetries at different pressures. The transition between these crystalline phases is determined theoretically through the bulk modulus from the relationship between material energy and volume. However, the change in the material molecular structure is responsible for the piezoelectric effect. In this study, density functional theory calculations using the Becke 3-Parameter-Lee-Yang-Parr hybrid functional were employed to investigate the structure and properties associated with the transition state of the tetragonal-cubic phase change in PbTiO3 material.

Development of a three-dimensional nonlinear viscoelastic constitutive model of solid propellant

A three dimensional nonlinear viscoelastic constitutive model for the solid propellant is developed. In their earlier work, the authors have developed an isotropic constitutive model and verified it for one dimensional case. In the present work, the validity of the model is extended to three-dimensional cases. Large deformation, dewetting and cyclic loading effects are treated as the main sources of nonlinear behavior of the solid propellant. Viscoelastic dewetting criteria is used and the softening of the solid propellant due to dewetting is treated by the modulus decrease. The nonlinearities during cyclic loading are accounted for by the functions of the octahedral shear strain measure. The constitutive equation is implemented into a finite element code for the analysis of propellant grains. A commercial finite element package ‘ABAQUS’ is used for the analysis and the model is introduced into the code through a user subroutine. The model is evaluated with different loading conditions and the predicted values are in good agreement with the measured ones. The resulting model applied to analyze a solid propellant grain for the thermal cycling load.