Electrochemical storage properties of polyaniline-, poly(N-methylaniline)-, and poly(N-ethylaniline)-coated pencil graphite electrodes

Three types of conducting polymers, polyaniline (PANI), poly(N-methylaniline) (PNMA), poly(N-ethylaniline) (PNEA) were electrochemically deposited on pencil graphite electrode (PGE) surfaces characterized as electrode active materials for supercapacitor applications. The obtained films were electrochemically characterized using different electrochemical methods. Redox parameters, electro-active characteristics, and electrostability of the polymer films were investigated via cyclic voltammetry (CV). Doping types of the polymer films were determined by the Mott-Schottky method. Electrochemical capacitance properties of the polymer film coating PGE (PGE/PANI, PGE/PNMA, and PGE/PNEA) were investigated by the CV and potentiostatic electrochemical impedance spectroscopy (EIS) methods in a 0.1 M H₂SO₄ aqueous solution. Thus, capacitance values of the electrodes were calculated. Results show that PGE/PANI, PGE/PNMA, and PGE/PNEA exhibit maximum specific capacitances of 131.78 F g^?1 (≈ 436.50 mF cm^?2), 38.00 F g^?1 (≈ 130.70 mF cm^?2), and 16.50 F g^?1 (≈ 57.83 mF cm^?2), respectively. Moreover, charge-discharge capacities of the electrodes are reported and the specific power (SP) and specific energy (SE) values of the electrodes as supercapacitor materials were calculated using repeating chronopotentiometry.     

An experimental and three-dimensional numerical study on the convective heat transfer inside a trapezoidal duct under constant wall temperature

In this study, steady-state forced convection heat transfer and pressure drop characteristics for hydrodynamically fully developed thermally developing three-dimensional turbulent flow in a horizontal smooth trapezoidal duct with corner angle of 75° and hydraulic diameter of 0.043 m were both experimentally and numerically investigated in the Reynolds number range from 2.6 × 10³ to 67 × 10³ for isothermal conditions. Results have shown that there is a good agreement between the present experimental and numerical results.     

The estimation of the Z′ gauge boson mass in E 6 models

The aim of this study is to estimate the Z′ boson mass by using the calculations of the decay width of Z′(ϑ) boson. So, the decay width of the extra Z boson is calculated numerically in effective rank 5 models for different mixing angles ϑ of the model and for different mass values of the extra Z boson. The decay width of Z′ boson to the Standard Model (SM) fermions is found to be between 4.42 and 19.36 GeV and the full decay width of Z′ boson to all particles is found to be between 20.88 and 37.15 GeV. We calculated the full decay width at the angle ϑ ≊ 0 for Z′ and Z ₂ → Z′. The full decay width of Z′ boson is written in a single equation according to our calculations. By using these calculations and the previous works the mass of Z′ boson and the number of generations of the exotic particles are estimated. The article is published in the original.     

Preparation of Pt/polypyrrole-ferrocene hydrogen peroxide sensitive electrode for the use as a biosensor

A polypyrrole electrode with ferrocene mediator is prepared and its sensitivity to hydrogen peroxide is investigated. The polypyrrole is deposited upon a 0.5 cm² Pt plate by the polymerization of pyrrole by scanning the electrode potential between 0.0 and 0.9 V at a scan rate of 50 mV/s. The platinum/polypyrrole-ferrocene (Pt/PPy-Fc) electrode is prepared by adding ferrocene to the coverage medium. The electrode’s sensitivity to hydrogen peroxide is investigated at room temperature using 0.025 M phosphate buffer at pH 7. The working potential is 0.7 V, the concentrations of pyrrole and ferrocene are 0.2 M and 10 mM. Polypyrrole was coated on the electrode surface within 26 cycles. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 2, pp. 160–164. The text was submitted by the authors in English.     

Synthesis and characterisation of novel chelating resin for selective preconcentration and trace determination of Pb(II) ions in aqueous samples by innovative microsample injection system coupled flame atomic absorption spectrometry

Expanded polystyrene (EPS) foam waste (white pollutant) was utilised for the synthesis of novel chelating resin i.e. EPS-N = N-α-Benzoin oxime (EPS-N = N-Box). The synthesised resin was characterised by FT-IR spectroscopy, elemental analysis, and thermogravimetric analysis. A selective method for the preconcentration of Pb(II) ions on EPS-N = N-Box resin packed in mini-column was developed. The sorbed Pb(II) ions were eluted with 5.0 mL of 2.0 mol L^?1 HCl and determined by microsample injection system coupled flame atomic absorption spectrometry (MIS-FAAS). The average recovery of Pb(II) ions was achieved 95.5% at optimum parameters such as pH 7, resin amount 400 mg, flow rates 1.0 mL min^?1 (of eluent) and3.0 mL min^?1 (of sample solution). The total saturation capacity of the resin, limit of detection (LOD) and limit of quantification (LOQ) of Pb(II) ions were found to be 30 mg g^?1, 0.033 μg L^?1 and 0.107 μg L^?1, respectively with preconcentration factor of 300. The accuracy, selectivity and validation of the method was checked by analysis of sea water (BCR-403), wastewater (BCR-715) and Tibet soil (NCS DC-78302) as certified reference materials (CRMs). The proposed method was applied successfully for the trace determination of Pb(II) ions in aqueous samples.     

On a characterization of the uniform distribution by generalized order statistics

In this paper a new variant of the Choquet-Deny theorem is obtained and used to prove a characterization of the uniform distribution based on spacings of generalized order statistics. This result extends two recent characterizations of the uniform distribution.     

Surface modifications of materials by repetitive laser pulses

Laser-induced modifications on platinum (Pt) and silicon (Si) are compared by considering the development of various features on the irradiated surface. The experiments were carried out both in air and under vacuum. The interaction of 50 pulses of 1064 nm Nd:YAG laser with both targets in air resulted in non-linear phenomena. The periphery of the irradiated spot on the Pt surface exhibits wave-like patterns with a featureless central portion. A non-uniform distribution of cones of different sizes is also observed on the irradiated surface. In the case of silicon, the laser-induced periodic surface structures along with the formation of micro-column, rectangular blocks and grid are prominently observed features. However, when both the targets were irradiated with the same number of shots under vacuum (～10^?3 Torr), the surface morphologies of both the targets exhibited the hydrodynamic sputtering but with more explosive expulsion in Pt when compared with silicon. In platinum, there is a periodic variation in the distance between adjacent cones formed in various ablated zones. The Gaussian beam mode TEM₀₀ provided the evidences for melt pool formation in silicon when irradiated under vacuum. Additionally, we observed other mechanisms including splashing, sputtering, burning, re-solidification and redeposition on the surface of irradiated targets.     

Do students really understand what an ordinary differential equation is?

Differential equations (DEs) are important in mathematics as well as in science and the social sciences. Thus, the study of DEs has been included in various courses in different departments in higher education. The importance of DEs has attracted the attention of many researchers who have generally focussed on the content and instruction of DEs. However, DEs are complex issues that students may find difficulty to understand. The limited research in this literature points to the need for more studies on students’ conceptions, and understanding of DEs and their basic concepts. The objective of this study is to fill this need by revealing the understanding, difficulties and weaknesses of the students who are successful in algebraic solutions, in relation to the concepts of DEs and their solutions. For this purpose, 77 students were asked 13 DE questions (6 of them about algebraic solution, and the rest about interpreting DEs and their solutions). From an analysis of the students’ answers, it was concluded that the students who were quite successful in algebraic solutions, indeed did not fully understand the related concepts, and they had serious difficulties in relation to these concepts.