Square Wave Adsorptive Stripping Voltammetry Determination of Chlorpyriphos in Irrigation Agricultural Water

This work describes the electroanalytical determination of Chlorpyriphos pesticide in natural waters using hanging mercury drop electrode allied to square wave adsorptive cathodic stripping voltammetry. The best responses were obtained in Britton?Robinson buffer solutions at pH 2.0, using a frequency of 100 s^–1, a scan increment of 5 mV, a square wave amplitude of 25 mV and an accumulation potential of–0.4 V during 60 s. Therefore, voltammetric responses showed the presence of one well-defined and irreversible reduction peak, at–1.08 V vs. Ag/AgCl/KCl 1.0 M, which involves two electrons in the reduction of carbon?nitrogen bond in the N-heterocyclic system with the participation of protonation equilibrium preceding the electron transfer reaction. Analytical curves were constructed and compared to similar curves performed by gas chromatograph coupled to a selective nitrogen?phosphorus detector, which demonstrates that the proposed methodology is suitable for determining contamination by Chlorpyriphos in complex samples.     

Multistability and the control of complexity

We show how multistability arises in nonlinear dynamics and discuss the properties of such a behavior. In particular, we show that most attractors are periodic in multistable systems, meaning that chaotic attractors are rare in such systems. After arguing that multistable systems have the general traits expected from a complex system, we pass to control them. Our controlling complexity ideas allow for both the stabilization and destabilization of any one of the coexisting states. The control of complexity differs from the standard control of chaos approach, an approach that makes use of the unstable periodic orbits embedded in an extended chaotic attractor. (c) 1997 American Institute of Physics.     

The Influence of the Electrodeposition Conditions on the Electroanalytical Performance of the Bismuth Film Electrode for Lead Determination

The bismuth film is a great promise as a suitable material to replace the mercury electrodes due to its low toxicity and good cathodic potential range. This work studies the influence of the electrodeposition conditions in the morphology and electroanalytical performance of the bismuth film electrodeposited onto copper electrode. The bismuth films were obtained in nitric or hydrochloric acid solutions with and without the presence of sodium citrate. The films were characterized by field emission scanning electron microscopy (FE‐SEM) and scanning electron microscopy with energy dispersive X‐ray spectrometry (SEM‐EDX). The microscopic analysis of the bismuth film obtained in HCl solution with sodium citrate (BIFE‐Cit) showed more homogeneous structure with higher content of bismuth than the film obtained in HCl only (BiFE‐HCl). The BiFE‐Cit exhibited a better analytical performance for lead with good adherence to the copper substrate.     

Heart rate variability analysis by chaotic global techniques in children with attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is characterized by decreased attention span, impulsiveness, and hyperactivity. Autonomic nervous system imbalance was previously described in this population. We aim to compare the autonomic function of children with ADHD and controls by analyzing heart rate variability (HRV). Children with ADHD (22 boys, mean age 9.964 years) and 28 controls (15 boys, mean age 9.857 years) rested in supine position with spontaneous breathing for 20 min. Heart rate was recorded beat by beat. HRV analysis was performed by use of chaotic global techniques. ADHD promoted an increase in the chaotic forward parameter. The algorithm which applied all three chaotic global parameters was only the second optimum statistically measured by Kruskal–Wallis (P < 0.0001) and low standard deviations. It was also highly influential by principal component analysis with almost all variation covered by the first two components. The third algorithm which lacked the (high spectral Detrended Fluctuation Analysis) parameter performed best statistically. However, we chose the algorithm which applied all three chaotic globals due to previous studies mentioned in the text—forward and inverse problems. Comparison of the autonomic function by analyzing HRV with chaotic global techniques suggests an increase in chaotic activity in children with ADHD in relation to the control group. © 2015 Wiley Periodicals, Inc. Complexity 21: 412–419, 2016     

Antioxidant capacity and in vitro prevention of dental plaque formation by extracts and condensed tannins of Paullinia cupana

Chemical evaluation of the semi-purified fraction from the seeds of guaraná, Paullinia cupana H.B.K. var. sorbilis (Mart.) Ducke, yielded the following compounds: caffeine, catechin, epicatechin, ent-epicatechin, and procyanidins B1, B2, B3, B4, A2, and C1. Measurement of the antioxidant activity by reduction of the DPPH radical confirmed the anti-radical properties of the aqueous (AqE) and crude (EBPC) extracts and semi-purified (EPA and EPB) fractions. The EPA fraction showed radical-scavenging activity (RSA) and protected DPPH from discoloration at 5.23 +/- 0.08 (RSD% = 1.49) microg/mL, and for the phosphomolybdenum complex showed a higher Relative Antioxidant Capacity (RAC) at 0.75 +/- 0.01 (1.75). The EPA fraction had a total polyphenolics content of 65.80% +/- 0.62 (RSD% = 0.93). The plant drug showed 5.47% +/- 0.19 (RSD% = 3.51) and 6.19% +/- 0.08 (RSD% = 1.29) for total polyphenolics and methylxanthines, respectively. In vitro assessment of the antibacterial potential of the Paullinia cupana extracts against Streptococcus mutans showed that these could be used in the prevention of bacterial dental plaque.     

Highly luminescent CdTe/CdSe colloidal heteronanocrystals with temperature-dependent emission color

In this work we present the preparation of highly luminescent anisotropic CdTe/CdSe colloidal heteronanocrystals. The reaction conditions used (low temperature, slow precursor addition, and surfactant composition) resulted in a tunable shape from prolate to branched CdTe/CdSe nanocrystals. Upon CdSe shell growth the heteronanocrystals show a gradual evolution from type-I to type-II optical behavior. These heteronanocrystals show a remarkably high photoluminescence quantum yield (up to 82%) and negligible thermally induced quenching up to temperatures as high as 373 K.     

A finite element model of localized deformation in frictional materials taking a strong discontinuity approach

A finite element model of localized deformation in frictional materials taking a strong discontinuity approach is presented. A rate-independent, non-associated, strain-softening Drucker–Prager plasticity model is formulated in the context of strong discontinuities and implemented along with an enhanced quadrilateral element within the framework of an assumed enhanced strain finite element method. For simple model problems such as uniform compression, the strong discontinuity approach has been shown to lead to mesh-independent finite element solutions when localized deformation is present. In this paper, a finite element analysis of localized deformation occurring in a more complex model problem of slope stability is conducted in a nearly mesh-independent manner. The effect of dilatancy on the orientation of slip lines is demonstrated for the slope stability problem.     

Vibrational and Rotational Spectroscopy of 13CD3OD

We have used Fourier Transform spectral data on the C-O stretching mode of ¹³CD₃OD in order to perform a vibro-rotational analysis for this molecule. We have estimated a few molecular parameters of the ground and C-O stretching vibrational modes. Based on these parameters, and by using the Kwan-Dennison model, we propose assignments for a number of far-infrared laser transitions of ¹³CD₃OD.