Electroanalytical Determination of Carbaryl in Natural Waters on Boron Doped Diamond Electrode

The anodic voltammetric behavior of carbaryl on a boron‐doped diamond electrode in aqueous solution is reported. The results, obtained by square‐wave voltammetry at 0.1 mol L^?1 Na₂SO₄ and pH 6.0, allow the development of a method to determine carbaryl, without any previous step of extraction, clean‐up, preconcentration or derivatization, in the range 2.5–30.0×10^?6 mol L^?1, with a detection limit of 8.2±0.2 μg L^?1 in pure water. The analytical sensitivity of this electrochemical method diminished slightly, from 3.07 mA mmol^?1 L to 2.90 mA mmol^?1L, when the electrolyte was prepared with water samples collected from two polluted points in an urban creek. In these conditions, the recovery efficiencies obtained were around 104%. The effect of other pesticides (fenthion and 4‐nitrophenol) was evaluated and found to exert a negligible influence on carbaryl determination. The square‐wave voltammetric data obtained for carbaryl were typical of an irreversible electrode process with mass transport control. The combination of square‐wave voltammetry and diamond electrodes is an interesting and desirable alternative for analytical determinations.     

Characterization and Use of Copper Solid Amalgam Electrode for Electroanalytical Determination of Triazines‐Based Herbicides

This paper reports the construction, characterization and use of copper solid amalgam electrode in the study of the electrochemical behavior of atrazine and ametryne herbicides by square‐wave voltammetry. This study was used as basis for the development of sensitive analytical methods for the determination of these herbicides in natural water, avoiding the use of mercury, by means of a solid electrode that presents high sensitivity and minimizes any environment contamination with mercury residues. The experimental and voltammetric conditions were evaluated and the results showed a reduction peak for atrazine at ?0.98 and at ?1.1 V vs. Ag/AgCl 3.0 mol L^?1 for ametryne, both with characteristic of an irreversible electrode reaction in an electrochemical diffusion controlled process, involving two electrons for each herbicide reduction. Based on voltammetric studies, it has been demonstrated that the most possible mechanism for the reduction of herbicides involved reduction of bond carbon‐chloride for atrazine and the reduction of bond carbon–SCH₃ for ametryne. The detection limit of herbicides obtained in pure water (laboratory samples) was shown to be lower than the maximum limit of residue established for natural water by the Brazilian Environmental Agency, demonstrating that this methodology is very suitable for determining any contamination by atrazine and ametryne residues in different samples, proving a good substitute for mercury electrodes.     

Existence of stationary turbulent flows with variable positive vortex intensity

We prove the existence of stationary turbulent flows with arbitrary positive vortex circulation on non-simply connected domains. Our construction yields solutions for all real values of the inverse temperature with the exception of a quantized set, for which blow-up phenomena may occur. Our results complete the analysis initiated in Ricciardi and Zecca (2016).     

Improved square coloring of planar graphs

Square coloring is a variant of graph coloring where vertices within distance two must receive different colors. When considering planar graphs, the most famous conjecture (Wegner, 1977) states that $\frac{3}{2}\mathrm{\Delta }+1$ colors are sufficient to square color every planar graph of maximum degree Δ. This conjecture has been proven asymptotically for graphs with large maximum degree. We consider here planar graphs with small maximum degree and show that $2\mathrm{\Delta }+7$ colors are sufficient, which improves the best known bounds when $6?\mathrm{\Delta }?31$.     

Electrochemical Monitoring of Methotrexate Anticancer Drug in Human Blood Serum by Using in situ Solvothermal Synthesized Fe3O4/ITO Electrode

Here, we reported on a one‐step fabrication of magnetite Fe₃O₄ nanoparticles/indium tin oxide (ITO) electrode based on the direct growing of Fe₃O₄ nanoparticles on the ITO surface by using a solvothermal process. The modified electrode was used as electrochemical methotrexate (MTX) biosensor with high sensitivity based on cyclic voltammetry and square wave voltammetry techniques. The results demonstrated a linear relationship between the MTX concentration and its oxidation current peak over a wide range from 10^?5 to 10^?14 mole/L with a limit of detection of 0.4×10^?15 M based on the square wave voltammetry (SWV) technique. In addition, Fe₃O₄/ITO electrode showed a good capability for measuring very low concentrations of MTX drug dissolved in human serum solution. Also, Fe₃O₄/ITO electrode was used for detecting MTX in blood serum samples collected from patients after their treatment with MTX. The prepared electrode showed the higher sensitivity that higher than the Viva‐E instrument, which opens the door for developing a cheap, simple and higher sensitive MTX sensor.     

联合Kalman和自适应Meanshift的稳健相关视频跟踪方法

相关视频跟踪器存在计算量大、模板漂移、对机动目标,杂波影响大以及遮挡情况无法跟踪的问题,而Kalman滤波能通过利用相关跟踪器的输出结果来预测目标在下一帧里在图像中的坐标,可以在高概率的小范围内对目标进行搜索,以大幅减小计算量和杂波的影响.然后,当跟踪器由于受到杂波或遮挡的影响而提供了错误的测量信息时,跟踪的性能将大幅下降.大量研究表明,Mean-Shift跟踪器具有运算速度快和跟踪性能好的特点,而当目标柱状图和待选图像区域相近时,其跟踪性能也将大幅下降,甚至无法进行跟踪.为了解决该问题,结合上述3种思想提出了一种改进的、稳健的视频目标跟踪方法,并通过理论分析和仿真结果表明了算法的有效性和优越性.     

Voltammetric Determination of Boric Acid Using the Ternary Complexation System with Salicylaldehyde and H‐Acid

A square‐wave voltammetric method for the determination of boric acid in water has been described based on the new understanding of the electrochemical behavior of boric acid‐Azomethine H complexation. Salicylaldehyde and H‐acid were used as the starting materials of boric acid‐Azomethine H complex and their concentrations were optimized for boric acid determination in water. A glassy carbon electrode, instead of a conventional mercury electrode, was used in the measurement. The detection limit of the proposed method was 0.10 mg B dm^?3. The proposed method was successfully used for boric acid determination in the water from a seawater desalination RO plant.     

Microsensor Chip Integrated with Gold Nanoparticles‐Modified Ultramicroelectrode Array for Improved Electroanalytical Measurement of Copper Ions

This paper presents a microsensor chip integrated with a gold nanoparticles‐modified ultramicroelectrode array (UMEA) as the working electrode for the detection of copper ions in water. The microsensor chip was fabricated with Micro‐Electromechanical System technique. Gold nanoparticles were electrodeposited onto the surface of UMEA at a constant potential of ?0.3 V. The ratio d/R_b of interelectrode spacing (d) over the individual electrode’s radius (R_b) was investigated to improve the electrochemical performance. The UMEA with a d/R_b of 20 showed the best hemispherical diffusion mode, resulted in fast response time and high current response. The gold nanoparticles increased the active surface area of UMEA by not changing the geometries of UMEA, and the current response was increased further. Incorporating the optimized characteristic of UMEA and gold nanoparticles, the microsensor showed a good linear range from 0.5 to 200 µg L^?1 of copper ions in the acetate buffer solutions with the method of square wave stripping voltammetry. Compared with the gold nanoparticles‐modified disk electrode, the gold nanoparticles‐modified UMEA showed higher sensitivity (0.024 µA mm^?2 µg^?1 L) and lower limit of detection (0.2 µg L^?1). Water samples from river water and tap water were analyzed by the microsensor chip with recovery ranging from 100.7 % to 107.8 %.     

Evaluation of a platinum electrode modified with hydroxyapatite in the lead(II) determination in a square wave voltammetric procedure

The behavior of a modified carbon platinum electrode (Pt) for lead(II) determination by square wave voltammetry (SWV) was studied. The modified electrode is obtained by electrodeposition of hydroxyapatite (HAP) on the surface of a bare platinum electrode. The new electrode (HAP/Pt) revealed interesting electroanalytical detection of lead(II) based on the adsorption of this metal onto hydroxyapatite under open circuit conditions. After optimization of the experimental and voltammetric conditions, the best voltammetric responses-current intensity and voltammetric profile were obtained in 0.2 mol L^?1 KNO₃ with: 30 min accumulation time, 5 mV pulse amplitude and 1 mV s^?1 scan rate. The observed detection (DL, 3σ) and quantification (DL, 10σ) limits in pure water were 2.01 × 10^?8 and 6.7 × 10^?7 mol L^?1, respectively. The reproducibility of the proposed method was determined from five different measurements in a solution containing 2.2 × 10^?6 mol L^?1 lead(II) with a coefficients of variation of 2.08%.The electrochemical of hydroxyapatite at platinum surfaces was characterized, after calcinations 900 °C, by X-ray diffraction, infrared spectroscopy, chemical and electrochemical analysis.