Determination of cadmium in river water samples by flame AAS after on-line preconcentration in mini-column packed with 2-aminothiazole-modified silica gel

A rapid and sensitive method was developed to determine trace levels of Cd2+ ions in an aqueous medium by flame atomic absorption spectrometry, using on-line preconcentration in a mini-column packed with 100 mg of 2-aminothiazol modified silica gel (SiAT). The Cd2+ ions were sorbed at pH 5.0. The preconcentrated Cd2+ ions were directly eluted from the column to the spectrometer's nebulizer-burner system using 100 μL of 2 mol L-1 hydrochloric acid. A retention efficiency of over 95% was achieved. The enrichment factor (calculated as the ratio of slopes of the calibration graphs) obtained with preconcentrations in a mini-column packed with SiAT (A = -1.3 × 10-3 + 1.8 × 10-3 [Cd2+]) and without preconcentrations (A = 4 × 10-5 + 3.5 × 10-3[Cd2+]), was 51 and the detection limit calculated was 0.38 μg L-1. The preconcentration procedure was applied to determine trace levels of Cd in river water samples. The optimum preconcentration conditions are discussed herein.

Rapid determination of zinc in foods by flow injection analysis with flame AAS using gradient calibration method

A calibration method was developed using flow injection analysis (FI) with a Gradient Calibration Method (GCM). The method allows the rapid determination of zinc In foods (approximately 30 min) after treatment with concentrated sulphuric acid and 30% hydrogen peroxide, and analysis with flame atomic absorption spectrometry (FAAS). The method provides analytical results with a relative standard deviation of about 2% and requires less time than by conventional FI calibration. The electronic selection of different segments along the gradient and monitoring of the technique covers wide concentration ranges while maintaining the inherent high precision of flow injection analysis. Concentrations, flow rates, and flow times of the reagents were optimized in order to obtain best accuracy and precision. Flow rates of 10 mL/min were selected for zinc. In addition, the system enables electronic dilution and calibration where a multipoint curve can be constructed using a single sample injection.

Active flutter suppression in a 2-D airfoil using linear matrix inequalities techniques

Flutter is an in-flight vibration of flexible structures caused by energy in the airstream absorbed by the lifting surface. This aeroelastic phenomenon is a problem of considerable interest in the aeronautic industry, because flutter is a potentially destructive instability resulting from an interaction between aerodynamic, inertial, and elastic forces. To overcome this effect, it is possible to use passive or active methodologies, but passive control adds mass to the structure and it is, therefore, undesirable. Thus, in this paper, the goal is to use linear matrix inequalities (LMIs) techniques to design an active state-feedback control to suppress flutter. Due to unmeasurable aerodynamic-lag states, one needs to use a dynamic observer. So, LMIs also were applied to design a state-estimator. The simulated model, consists of a classical flat plate in a two-dimensional flow. Two regulators were designed, the first one is a non-robust design for parametric variation and the second one is a robust control design, both designed by using LMIs. The parametric uncertainties are modeled through polytopic uncertainties. The paper concludes with numerical simulations for each controller. The open-loop and closed-loop responses are also compared and the results show the flutter suppression. The perfomance for both controllers are compared and discussed. Copyright © 2006 by ABCM.

The influence of the flame structure on the combustion oscillations in a cylindrical chamber

An experimental study has been conducted with the objective of investigating the effects of the flame structure in the combustion oscillation conditions into a laboratorial scale cylindrical chamber. The experiments were conducted in a water-jacketed 1-m long by 25-cm internal diameter stainless steel vertical tube. The combustor operated with liquefied petroleum gas (LPG) in both oscillatory and non oscillatory conditions, under the same input conditions. Part of the reactant mixture was excited acoustically, before the burner exit, by a speaker positioned strategically. The burner was aligned with the chamber longitudinal axis and positioned at its bottom. The experiments were conducted for 0.16 g/s of LPG burning in stoichiometric equivalence ratio. To analyze the flame structure the image tomographic reconstruction process were used, and the resultant images were associated to the oscillatory conditions (frequency and amplitude) into the combustion chamber. The main conclusions were: 1) when the flame premixed condition increase, for example 60% of the total air flow rate is premixed with LPG, the region of intense energy released is close to burner exit and strong amplitudes of oscillation (close to 50 mbar) were obtained into the chamber; 2) for long flames, predominantly diffusive flames, just weak amplitudes were detected, in the spite of the speaker exiting the premixed flow; 3) when the energy is released distributed through the combustion chamber, the long flame acts like a baffle. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Determination of calcium and magnesium in hydroethanolic extracts of propolis by atomic absorption flame spectrophotometry

Propolis is a natural product collected by honeybees and has a large range of pharmacological activity, including antimicrobial, antitumoral, antioxidant and anti-inflammatory. Its use as a popular medicine is increasing all over the world, creating a need for quality control of the commercial products. In this study the levels of calcium and magnesium in commercial hydroalcoholic propolis extracts from varies states of Brazil were determined by atomic absorption flame spectrophotometry and different values were obtained for northern and southern states. This study can be extended to the analysis of metals that are harmful to health. The results showed that the calibration curves were linear over a wide concentration range (0.5-4.0 μg.mL -1 for calcium and 0.05-0.4 μg.mL -1 for magnesium) with good correlation coefficients (0.999 and 0.988, respectively). Good analytical recovery (94%) was obtained. The proposed method showed adequate precision and relative standard deviation lower than 2 %. The method is accurate and precise as well as having advantages such as simplicity and speed.

Determination of copper at wide range concentrations using instrumental features of high-resolution continuum source flame atomic absorption spectrometry

This work describes a method to determine Cu at wide range concentrations in a single run without need of further dilutions employing high-resolution continuum source flame atomic absorption spectrometry. Different atomic lines for Cu at 324. 754 nm, 327. 396 nm, 222. 570 nm, 249. 215 nm and 224. 426 nm were evaluated and main figures of merit established. Absorbance measurements at 324. 754 nm, 249. 215 nm and 224. 426 nm allows the determination of Cu in the 0. 07-5. 0 mg L -1, 5. 0-100 mg L -1 and 100-800 mg L -1 concentration intervals respectively with linear correlation coefficients better than 0. 998. Limits of detection were 21 μg L -1, 310 μg L -1 and 1400 μg L -1 for 324. 754 nm, 249. 215 nm and 224. 426 nm, respectively and relative standard deviations (n = 12) were ≤ 2. 7%. The proposed method was applied to water samples spiked with Cu and the results were in agreement at a 95% of confidence level (paired t-test) with those obtained by line-source flame atomic absorption spectrometry.

Chaos suppression in NEMs resonators by using nonlinear control design

In this work the chaotic behavior of a micro-mechanical resonator with electrostatic forces on both sides is suppressed. The aim is to control the system in an orbit of the analytical solution obtained by the Method of Multiple Scales. Two control strategies are used for controlling the trajectory of the system, namely: State Dependent Riccati Equation (SDRE) Control and Optimal Linear Feedback Control (OLFC). The controls proved effectiveness in controlling the trajectory of the system. Additionally, the robustness of each strategy is tested considering the presence of parametric errors and measurement noise in control. © 2012 American Institute of Physics.

Productivity and water suppression in different beans (Phaseolus vulgaris L.) phenological stages

Common Bean (Phaseolus vulgaris L.) is widespread in the social and economic scene in Brazil, as well it is Brazilian population main dish, and it also helps small and medium farmers' income. The objective of this study was to compare the productivity performance of common bean Carioca - IAC Alvorada with irrigation suppression in each of the five phenological phases. The experiment was conducted in plots in a greenhouse at College of Agronomical Sciences, São Paulo State University (UNESP), Botucatu - SP. The hypothesis is that if the water supply is suppressed in one of the five development stages of irrigated common beans, the yield reduction would be at least 20%. The treatments consisted of suppression irrigation in one of the five development stages (stage V1 to V3, stage V4 to early flowering, flowering stage, pod formation stage and pod filling stage) compared with the irrigation at all stages and suppression of irrigation at all stages, with seven treatments and four replications. The treatments most affected by water suppression were those which suffered suppression of irrigation during the vegetative phase and flowering stage. Treatments with water suppression in all stages, and suppression during the phases (stage V1 to V3, stage V4 to early flowering, flowering stage, pod formation stage and pod filling stage) showed yield reduction of approximately 95%, 55.1%, 49.5%, 63,1%, 30.2% and 35.6%, respectively, when compared to treatment with irrigation all stages. All treatments considered confirmed the hypothesis.

On the Chaotic Suppression of Both Ideal and Non-ideal Duffing Based Vibrating Systems, Using a Magnetorheological Damper

In this paper the dynamics of the ideal and non-ideal Duffing oscillator with chaotic behavior is considered. In order to suppress the chaotic behavior and to control the system, a control signal is introduced in the system dynamics. The control strategy involves the application of two control signals, a nonlinear feedforward control to maintain the controlled system in a periodic orbit, obtained by the harmonic balance method, and a state feedback control, obtained by the state dependent Riccati equation, to bring the system trajectory into the desired periodic orbit. Additionally, the control strategy includes an active magnetorheological damper to actuate on the system. The control force of the damper is a function of the electric current applied in the coil of the damper, that is based on the force given by the controller and on the velocity of the damper piston displacement. Numerical simulations demonstrate the effectiveness of the control strategy in leading the system from any initial condition to a desired orbit, and considering the mathematical model of the damper (MR), it was possible to control the force of the shock absorber (MR), by controlling the applied electric current in the coils of the damper. © 2012 Foundation for Scientific Research and Technological Innovation.

Sequential Determination of Cd, Cu and Pb in Tea Leaves by Slurry Introduction to Thermospray Flame Furnace Atomic Absorption Spectrometry

A simple procedure for the sequential determination of Cd, Cu and Pb in tea leaves by slurry introduction to thermospray flame furnace atomic absorption spectrometry was developed. Detection limits were 0.05 mg kg-1 for Cd, 2.1 mg kg-1 for Cu and 0.68 mg kg-1 for Pb using 0.67 % (m/v) slurries (100 mg/15 mL). © 2013 Springer Science+Business Media New York.

Evaluation of lines of boron, phosphorus and sulfur by high-resolution continuum source flame atomic absorption spectrometry for plant analysis

The wavelength-integrated absorbance (WIA) and summation of absorbance (∑ lines) of different lines were evaluated to enhance sensitivity and determine B, P and S in medicinal plants by HR-CS FAAS. The lowest LOD for B (0.5mgL-1) and P (13.7mgL-1) was obtained by integration of lines 249.773nm (3pixels) and 247.620nm (5pixels), respectively. The ∑ lines for CS at 257.595nm and 257.958nm furnished LOD=30.5mgL-1, ca. 10% lower than the LOD obtained for the WIA using 257.595nm and 5pixels. Data showed the advantage of WIA over ∑ lines to improve sensitivity for all analytes. Under optimized conditions, calibration curves in the 1.0-100mgL-1 B and 50.0-2000mgL-1 P, S ranges were consistently obtained. Results obtained with the HR-CS FAAS method were in agreement at 98% and 95% confidence level with certified values for B and P, respectively. And results for S were in accordance to non-certified values. Concentrations of B, P, and S in 12 medicinal plants analyzed by the proposed method varied within the 19.4-34.5mgkg-1 B, 719-3910mgkg-1 P and 1469-7653mgkg-1 S ranges. © 2012 Elsevier B.V.

Microcantilever chaotic motion suppression in tapping mode atomic force microscope

The tapping mode is one of the mostly employed techniques in atomic force microscopy due to its accurate imaging quality for a wide variety of surfaces. However, chaotic microcantilever motion impairs the obtention of accurate images from the sample surfaces. In order to investigate the problem the tapping mode atomic force microscope is modeled and chaotic motion is identified for a wide range of the parameter's values. Additionally, attempting to prevent the chaotic motion, two control techniques are implemented: the optimal linear feedback control and the time-delayed feedback control. The simulation results show the feasibility of the techniques for chaos control in the atomic force microscopy. © 2012 IMechE.

Subchronic effects of fluoxetine on conditioned suppression produced by a hot air blast

Conditioned suppression is an animal model of anxiety disorders that has been broadly used to investigate the behavioral effects of different drugs. However, various methodological variables (e.g., the type of aversive stimulus) that supposedly interfere with the acquisition of conditioned suppression may also contribute to conflicting results among the studied drugs. Additionally, few studies have sought to investigate the effects of selective serotonin reuptake inhibitors (SSRIs). The present study investigated the effect of subchronic 5-day administration of 5 mg/kg fluoxetine in the retention of conditioned suppression produced by a hot air blast (HAB). The subjects were 12 albino Wistar rats distributed into an Experimental Group (EG) and Control Group (CG). After sessions were conducted to pair two stimuli, a sound and HAB, fluoxetine (EG) or saline (CG) was administered. Twentyfour hours after the last injection, a test session was conducted. The results showed no difference between groups. Fluoxetine (5 mg/kg) did not exert anxiolytic effects in this model of conditioned suppression produced by a HAB. Keywords: conditioned suppression; fluoxetine; subchronic; hot air blast.

Cross linked Poly (4-Vinylpyridine-Ethylene Glycol Dimethacrylate) Used for Preconcentration of Cd(II) and its Determination by Flow Injection Flame Atomic Absorption Spectrometry

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Flame retardant properties of the bark powder of Anadenanthera peregrina var. falcata (Benth.) Altschul (angico) studied by coupled thermogravimetry-Fourier transform infrared spectroscopy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)