Ecophysiological response of Sorghum halepense populations to reduced rates of nicosulfuron

The control and regrowth after nicosulfuron reduced rate treatment of Johnsongrass (Sorghum halepense L. Pers.) populations, from seven Argentinean locations, were evaluated in pot experiments to assess if differential performance could limit the design and implementation of integrated weed management programs. Populations from humid regions registered a higher sensibility to reduced rates of nicosulfuron than populations from subhumid regions. This effect was visualised in the values of regression coefficient of the non-linear models (relating fresh weight to nicosulfuron rate), and in the time needed to obtain a 50% reduction of photosynthesis rate and stomatal conductance. The least leaf CO2 exchange of subhumid populations could result in a lower foliar absorption and translocation of nicosulfuron, thus producing less control and increasing their ability to sprout and produce new aerial biomass. The three populations from subhumid regions, with less sensibility to nicosulfuron rates, presented substantial difference in fresh weight, total rhizome length and number of rhizome nodes, when they were evaluated 20 week after treatment. In consequence, a substantial Johnsongrass re-infestation could occur, if rates below one-half of nicosulfuron labeled rate were used to control Johnsongrass in subhumid regions.

Base temperature and simulation model for nodes appearance in cape gooseberry (Physalis peruviana L.)

Data was analyzed on development of the solanaceen fruit crop Cape gooseberry to evaluate how well a classical thermal time model could describe node appearance in different environments. The data used in the analysis were obtained from experiments conducted in Colombia in open fields and greenhouse condition at two locations with different climate. An empirical, non linear segmented model was used to estimate the base temperature and to parameterize the model for simulation of node appearance vs. time. The base temperature (Tb) used to calculate the thermal time (TT, ºCd) for node appearance was estimated to be 6.29 ºC. The slope of the first linear segment was 0.023 nodes per TT and 0.008 for the second linear segment. The time at which the slope of node apperance changed was 1039.5 ºCd after transplanting, determined from a statistical analysis of model for the first segment. When these coefficients were used to predict node appearance at all locations, the model successfully fit the observed data (RSME=2.1), especially for the first segment where node appearance was more homogeneous than the second segment. More nodes were produced by plants grown under greenhouse conditions and minimum and maximum rates of node appearance rates were also higher.

O ajuste de funções matemáticas a dados experimentais

The least square method is analyzed. The basic aspects of the method are discussed. Emphasis is given in procedures that allow a simple memorization of the basic equations associated with the linear and non linear least square method, polinomial regression and multilinear method.

Study of the optical properties of TeO2-PbO-TiO2 glass system

We describe the preparation and some optical properties of high refractive index TeO2-PbO-TiO2 glass system. Highly homogeneous glasses were obtained by agitating the mixture during the melting process in an alumina crucible. The characterization was done by X-ray diffraction, Raman scattering, light absorption and linear refractive index measurements. The results show a change in the glass structure as the PbO content increases: the TeO4 trigonal bipyramids characteristics of TeO2 glasses transform into TeO3 trigonal pyramids. However, the measured refractive indices are almost independent of the glass composition. We show that third-order nonlinear optical susceptibilities calculated from the measured refractive indices using Lines' theoretical model are also independent of the glass composition.

Estudo das propriedades ópticas em vidros 0,3La2S3-0,7Ga2S 3

In this work we describe the synthesis and characterization of chalcogenide glass (0.3La2S3-0.7Ga2S 3) with low phonons frequencies. Several properties were measured like Sellmeier parameters, linear refractive index dispersion and material dispersion. Samples with the composition above were doped with Dy2S3. The absorption and emission characteristics were measured by electronic spectroscopy and fluorescence spectrum respectively. Raman and infrared spectroscopy shows that these glasses present low phonons frequencies and strucuture composed by GaS4 tetrahedrals. The Lines model was used for calculate the coefficients values of the non linear refractive index.

Métodos matemáticos para correção de interferências espectrais e efeitos interelementos na análise quantitativa por fluorescência de raios-X

One of the main problems in quantitative analysis of complex samples by x-ray fluorescence is related to interelemental (or matrix) effects. These effects appear as a result of interactions among sample elements, affecting the x-ray emission intensity in a non-linear manner. Basically, two main effects occur; intensity absorption and enhancement. The combination of these effects can lead to serious problems. Many studies have been carried out proposing mathematical methods to correct for these effects. Basic concepts and the main correction methods are discussed here.

Aplicação da equação de Poisson-Boltzmann ao cálculo de propriedades dependentes do pH em proteínas

The ability of biomolecules to catalyze chemical reactions is due chiefly to their sensitivity to variations of the pH in the surrounding environment. The reason for this is that they are made up of chemical groups whose ionization states are modulated by pH changes that are of the order of 0.4 units. The determination of the protonation states of such chemical groups as a function of conformation of the biomolecule and the pH of the environment can be useful in the elucidation of important biological processes from enzymatic catalysis to protein folding and molecular recognition. In the past 15 years, the theory of Poisson-Boltzmann has been successfully used to estimate the pKa of ionizable sites in proteins yielding results, which may differ by 0.1 unit from the experimental values. In this study, we review the theory of Poisson-Boltzmann under the perspective of its application to the calculation of pKa in proteins.

Comportamento dinâmico-mecânico e relaxações em polímeros e blendas poliméricas

Dynamic mechanical analysis (DMA) is widely used in materials characterization. In this work, we briefly introduce the main concepts related to this technique such as, linear and non-linear viscoelasticity, relaxation time, response of material when it is submitted to a sinusoidal or other periodic stress. Moreover, the main applications of this technique in polymers and polymer blends are also presented. The discussion includes: phase behavior, crystallization; spectrum of relaxation as a function of frequency or temperature; correlation between the material damping and its acoustic and mechanical properties.

Um estudo teórico relativo à não-linearidade da ligação de hidrogênio em sistemas heterocíclicos C2H4O-C2H2 e C2H4S-C2H2

B3LYP/6-31G(d,p) calculations were used to determine the optimized geometries of the C2H4O-C2H2 and C2H4S-C2H2 heterocyclic hydrogen-bonded complexes. Results of structural, rotational, electronic and vibrational parameters indicate that the hydrogen bonding is non-linear due to the pi bond of the acetylene interacting with the hydrogen atoms of the methyl groups of the three-membered rings. Moreover, the theoretical investigation showed that the non-linearity is much more intriguing, since there is a structural disjunction on the acetylene within the heterocyclic system.

Otimização da análise isotópica de UF6 utilizando-se a técnica de espectrometria de massas por quadrupolo

A procedure for determining of the isotope ratio 235U/238U in UF6 samples was established using a quadrupole mass spectrometer with ionization by electron impact. The following items were optimized in the spectrometer: the parameters in the ion source that provided the most intense peak, with good shape, for the most abundant isotope; the resolution that reduced the non linear effects and the number of analytical cycles that reduced the uncertainty in the results. The measurement process was characterized with respect to the effects of mass discrimination, linearity and memory effect.

Validação da metodologia da avaliação de incerteza em curvas de calibração melhor ajustadas por polinômios de segundo grau

The most widespread literature for the evaluation of uncertainty - GUM and Eurachem - does not describe explicitly how to deal with uncertainty of the concentration coming from non-linear calibration curves. This work had the objective of describing and validating a methodology, as recommended by the recent GUM Supplement approach, to evaluate the uncertainty through polynomial models of the second order. In the uncertainty determination of the concentration of benzatone (C) by chromatography, it is observed that the uncertainty of measurement between the methodology proposed and Monte Carlo Simulation, does not diverge by more than 0.0005 unit, thus validating the model proposed for one significant digit.

Thermodynamic study of the solubility of sodium naproxen in some ethanol + water mixtures

By using the van't Hoff and Gibbs equations the apparent thermodynamic functions Gibbs energy, enthalpy, and entropy of solution for sodium naproxen in ethanol + water cosolvent mixtures, were evaluated from solubility data determined at temperatures from (278.15 to 308.15) K. The drug solubility was greatest in neat water and lowest in neat ethanol at all the temperatures studied. By means of non-linear enthalpy-entropy compensation analysis, it follows that the dissolution process of this drug in ethanol-rich mixtures is entropy-driven, whereas, in water-rich mixtures the process is enthalpy-driven.

Thermodynamic study of the solubility of triclocarban in ethanol + propylene glycol mixtures

By using the van't Hoff and Gibbs equations the apparent thermodynamic functions Gibbs energy, enthalpy, and entropy of solution for triclocarban in ethanol + propylene glycol mixtures were evaluated from solubility data determined at temperatures from (293.15 to 313.15) K. The drug solubility was greatest in the mixture with 0.60 in mass fraction of ethanol and lowest in neat propylene glycol at almost all the temperatures studied. Non-linear enthalpy-entropy compensation is found indicating apparently different mechanisms of the solution process according to the mixtures composition.

Caracterização composicional e transesterificação de óleo de microalga: uma abordagem computacional

A procedure for compositional characterization of a microalgae oil is presented and applied to investigate a microalgae based biodiesel production process through process simulation. The methodology consists of: proposing a set of triacylglycerides (TAG) present in the oil; assuming an initial TAG composition and simulating the transesterification reaction (UNISIM Design, Honeywell) to obtain FAME characterization values (methyl ester composition); evaluating deviations of experimental from calculated values; minimizing the sum of squared deviations by a non-linear optimization algorithm, with TAG molar fractions as decision variables. Biodiesel from the characterized oil is compared to a rapeseed based biodiesel.

Solution thermodynamics of methocarbamol in some ethanol + water mixtures

Apparent thermodynamic functions, Gibbs energy, enthalpy and entropy of solution and mixing, for methocarbamol in ethanol + water mixtures, were evaluated from solubility data determined at temperatures from 293.15 K to 313.15 K and from calorimetric values of drug fusion. The drug solubility was greatest in the mixtures with 0.70 or 0.80 mass fraction of ethanol and lowest in neat water across all temperatures studied. Non-linear enthalpy-entropy compensation was found for the dissolution processes. Accordingly, solution enthalpy drives the respective processes in almost all the solvent systems analyzed.