Supercritical carbon dioxide extraction of bioactive flavonoid from Strobilanthes crispus (Pecah Kaca)

The bioactive flavonoid compounds of Strobilanthes crispus (Pecah Kaca) leaves obtained by using supercritical carbon dioxide (SC-CO₂) extraction were investigated and the obtained crude extract yields were compared in order to select the best operation parameters. Since carbon dioxide is a non-polar solvent, ethanol was used as co-solvent to increase the polarity of the fluid. The studied parameters were pressure (100, 150 and 200 bar), temperature (40, 50 and 60 °C) and dynamic extraction time (40, 60 and 80 min). The optimum extraction condition occurred at 200 bar, 50 °C and 60 min. Based on the mean value, pressure had dominant effect on the extraction yield. Apart from the optimum SFE conditions two other conditions namely at minimum (100 bar, 40 °C, 40 min) and maximum (200 bar, 60 °C, 80 min) levels of each studied parameters as control runs were analyzed by HPLC to determine the major bioactive flavonoid compounds from S. crispus. Under the optimum conditions eight flavonoid compounds were identified; they were (+)-catechin, (?)-epicatechin, rutin, myricetin, luteolin, apigenin, naringenin and kaempferol.     

Unique microstructure analysis of ethylene-propylene copolymer synthesized using catalytic system based on α-diimine nickel complexes: a comparative study by 13C NMR technique

The microstructure of rubber-like ethylene-propylene copolymer (MN4) produced by a mixed nickel-based system (MN) containing catalysts of dibromo[N,N′-bis(2,6-diisopropylphenyl)-2,3-butanediimine]nickel(II) n1 and dibromo[N,N′-(phenanthrene-9,10-diylidene)bis(2,6-diisopropylaniline)]nickel(II) n2 was determined by ¹³C NMR technique. Sequences distribution of ethylene (E), propylene (P), EP, inverted propylene and uninterrupted methylene and also methylene number-average sequence lengths for the copolymer (MN4) were estimated. The results obtained from the MN4 EP copolymer were compared with reported copolymers which had been synthesized using constrained geometry catalyst (CGC) and vanadium-based Ziegler-Natta catalyst. The results demonstrated that the MN4 EP copolymer had fewer alternating comonomer sequences than ethylene-propylene elastomers obtained by CGC and vanadium-based (V) catalysts. A large number of the inversion structures (66 %) and high mole percent of sequences containing a long branch (3.2 mol%) were also observed in unique microstructure of the copolymer (MN4).     

Electrical double-layer capacitors: evaluation of ageing phenomena during cycle life testing

This paper represents an assessment of the main ageing phenomena in electrical double-layer capacitors (EDLCs). In this study the cycle life of the EDLC cells with a rated capacitance of 1,600 F has been investigated at different ambient temperatures and current rates. From the experimental results we can observe that the impact of the high ambient temperature is significant on the cycle life of the cells. Moreover, the results also show the negative impact of the current rate. The internal resistance tests showed that the increase of the resistance is much higher than the decrease of the capacitance. Thus, the ageing of the EDLC during cycling was clearly non-linear. Further the EIS measurements indicated the higher increase of the imaginary part of the impedance at low frequencies during cycling, which indicates the capacitance fade.     

Study on Wear Model and Adhesive Wear Mechanism of Brass under Boundary Lubrication

Protection of Metals and Physical Chemistry of Surfaces - The tribological tests of brass and steel are carried out on an in-situ tribometer. The Stribeck curve illustrates that the roughness and...     

Hematoxylin multi-wall carbon nanotubes modified glassy carbon electrode for electrocatalytic oxidation of hydrazine

A new hydrazine sensor has been fabricated by immobilizing hematoxylin at the surface of a glassy carbon electrode (GCE) modified with multi-wall carbon nanotube (MWCNT). The adsorbed thin films of hematoxylin on the MWCNT modified GCE show one pair of peaks with surface confined characteristics. The hematoxylin MWCNT (HMWCNT) modified GCE shows highly catalytic activity toward hydrazine electro-oxidation. The results show that the peak potential of hydrazine at HMWCNT modified GCE surface shifted by about 167 and 255 mV toward negative values compared with that at an MWCNT and activated modified GCE surface, respectively. In addition, at HMWCNT modified electrode surface remarkably improvement the sensitivity of determination of hydrazine. The kinetic parameters, such as the electron transfer coefficient, α, and the standard heterogeneous rate constant, k⁰, for oxidation of hydrazine at the HMWCNT modified GCE were determined and also is shown that the heterogeneous rate constant, k′, is strongly potential dependent. The overall number of electron involved in the catalytic oxidation of hydrazine and the number of electrons involved in the rate-determining steps are 2 and 1, respectively. The amperometric detection of hydrazine is carried out at 220 mV in 0.1 M phosphate buffer solution (pH 7) with linear response range 2.0-122.8 μM hydrazine, detection limit of 0.68 μM and sensitivity of 0.0208 μA μM⁻¹. Finally the amperometric response for hydrazine determination is reproducible, fast and extremely stable, with no loss in sensitivity over a continual 400 s operation.     

Soft-templating pathway to create nanostructured Mg–Al spinel as high-temperature absorbent for SO2

Interest in reducing SO₂ emission from the fluid catalytic cracking (FCC) crude oil has been encouraging the development of new materials to achieve such goal. The nanostructured Mg–Al spinel (MgAl₂O₄) was prepared by co-precipitation and post hydrothermal treatment in the presence of glucose and followed by elimination of the organic components by calcination at 700 °C for 3 h. Physical and chemical properties were characterized by XRD, N₂ sorption, TG, FTIR, SEM, and TEM methods. Mesoporous nanostructured MgAl₂O₄ with a high surface area of 324 m² g^?1 were obtained. The organic components contributed to the development of mesoporosity, functioning as a soft template. SO₂ adsorption tests showed that the nanostructured MgAl₂O₄ had a 51.58 % increase of SO₂ sorption capacity than MgAl₂O₄ prepared without glucose. These results showed that the nanostructured MgAl₂O₄ is a promising candidate as catalyst for flue gas desulfurization in FCC process. Three kinetic models were also applied to analyze the SO₂ adsorption kinetics; the pseudo-second order kinetic model fit well with a correlation coefficient (R²) of 0.991 for nanostructured MgAl₂O₄.     

Cathodic electrodeposition of Y(OH)3 and Y2O3 nanostructures from chloride bath. Part II: Effect of the bath temperature on the crystal structure,composition and morphology

Ultra-fine nanoparticles, mono-dispersed nanospheres and nanorods of Y(OH)₃ and Y₂O₃ were successfully prepared via electrodeposition from chloride bath at different temperatures of 10, 25, 40 and 80 °C followed by heat-treatments at 600 °C in dry air atmosphere. Thermal behavior of the hydroxide samples was investigated by differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. The structural and morphological characteristics of the products were determined by X-ray diffraction (XRD), FT-IR, scanning and transmission electron microscopy (SEM and TEM). Effects of bath temperature on the mechanism of base electrogeneration and deposit formation on the cathode surface were proposed and discussed. The results showed that the crystal structure, composition and morphology of the products are mainly affected by the temperature of electrodeposition bath.     

Impact of hydrogen concentrations on the impedance spectroscopic behavior of Pd-sensitized ZnO nanorods

ZnO nanorods were synthesized using a low-cost sol-gel spin coating technique. The synthesized nanorods were consisted of hexagonal phase having c-axis orientation. SEM images reflected perpendicular ZnO nanorods forming bridging network in some areas. The impact of different hydrogen concentrations on the Pd-sensitized ZnO nanorods was investigated using an impedance spectroscopy (IS). The grain boundary resistance (R_gb) significantly contributed to the sensing properties of hydrogen gas. The boundary resistance was decreased from 11.95 to 3.765 kΩ when the hydrogen concentration was increased from 40 to 360 ppm. IS gain curve showed a gain of 6.5 for 360 ppm of hydrogen at room temperature. Nyquist plot showed reduction in real part of impedance at low frequencies on exposure to different concentrations of hydrogen. Circuit equivalency was investigated by placing capacitors and resistors to identify the conduction mechanism according to complex impedance Nyquist plot. Variations in nanorod resistance and capacitance in response to the introduction of various concentrations of hydrogen gas were obtained from the alternating current impedance spectra.     

Discrete-time chaotic-map truly random number generators: design, implementation, and variability analysis of the zigzag map

In this paper, we introduce a novel discrete chaotic map named zigzag map that demonstrates excellent chaotic behaviors and can be utilized in truly random number generators (TRNGs). We comprehensively investigate the map and explore its critical chaotic characteristics and parameters. We further present two circuit implementations for the zigzag map based on the switched current technique as well as the current-mode affine interpolation of the breakpoints. In practice, implementation variations can deteriorate the quality of the output sequence as a result of variation of the chaotic map parameters. In order to quantify the impact of variations on the map performance, we model the variations using a combination of theoretical analysis and Monte-Carlo simulations on the circuits. We demonstrate that even in the presence of the map variations, a TRNG based on the zigzag map passes all of the NIST 800-22 statistical randomness tests using simple post processing of the output data.