Differential-pulse polarographic determination of the insecticide imidacloprid in commercial formulations

The reduction reaction of imidacloprid [1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine] at a mercury electrode shows two well-defined waves in the range of pH 2.0–11.0. The characteristics of the electrode processes were examined. The analyte captures four electrons in the first step and two in the second to give the hydroxylamine and amine derivatives, respectively. A differential-pulse polarographic method for the determination of imidacloprid based on the first reduction peak of this compound is presented. Britton-Robinson buffer was used as a supporting electrolyte and optimum pH value was found to be pH 8.O. The applicable concentration range was from 10 to 200 ng/ml, with a relative standard deviation of 1.5% (for a level of 80 ng/ml) and a detection limit of 3 ng/ml. The method has been satisfactorily applied to the determination of imidacloprid in commercial formulations.     

A computational work on turbulent flow and heat transfer in a channel fitted with inclined baffles

Numerical studies of momentum and heat transfer characteristics have been investigated of a steady incompressible turbulent flow of air through channel. The channel has inclined baffles which are arranged on the walls in a periodically staggered way. The governing equations, namely, continuity, Navier–Stokes and energy, based on k–ω turbulence model to describe the turbulence phenomenon are solved using the finite volume method and the SIMPLE algorithm. Calculations are performed for a Reynolds number between 12,000 and 38,000. The axial velocity profiles, the velocity fields, the local and average coefficient of friction and the Nusselt number distribution were obtained for all the geometry considered and for different sections selected, upstream, downstream and between the two inclined baffles. Simulation results which were obtained by the use of baffles are validated by an experimental study. Good agreement is observed between numerical and experimental results data in the literature.     

On the generalized virial theorem for systems with variable mass

We presently extend the virial theorem for both discrete and continuous systems of material points with variable mass, relying on developments presented in Ganghoffer (Int J Solids Struct 47:1209–1220, 2010). The developed framework is applicable to describe physical systems at very different scales, from the evolution of a population of biological cells accounting for growth to mass ejection phenomena occurring within a collection of gravitating objects at the very large astrophysical scales. As a starting basis, the field equations in continuum mechanics are written to account for a mass source and a mass flux, leading to a formulation of the virial theorem accounting for non-constant mass within the considered system. The scalar and tensorial forms of the virial theorem are then written successively in both Lagrangian and Eulerian formats, incorporating the mass flux. As an illustration, the averaged stress tensor in accreting gravitating solid bodies is evaluated based on the generalized virial theorem.     

Chemical composition of the essential oils of the berries of Juniperus oxycedrus L. ssp. rufescens (L. K.) and Juniperus oxycedrus L. ssp. macrocarpa (S. & m.) Ball. and their antioxidant activities

This study is outlined to probe the chemical composition of essential oil and in vitro antioxidant activity of Juniperus oxycedrus ssp. macrocarpa (S. & m.) Ball. and Juniperus oxycedrus L. ssp. rufescens (L. K.) berries, collected from four sites, according to their maturity phase. The chemical composition of the hydrodistilled essential oil was analysed by GC-MS. Forty-eight compounds were identified, accounting for approximately 79.8-98.9% of the oil. The main constituents were α-pinene, germacrene D, myrcene, abietadiene and cis-calamenene, their mean percentage vary according to their phenological stage. The antioxidant activity of the samples was determined by the ABTS and DPPH radical scavenging activities. Hawaria essential oil extracted from mature berries showed the highest antioxidant capacity.     

Two-dimensional polymeric nanomaterials through cross-linking of polybutadiene-b-poly(ethylene oxide) monolayers at the air/water interface

Two-dimensional polymeric nanomaterials consisting of a continuously cross-linked polybutadiene (PB) two-dimensional network with poly(ethylene oxide) (PEO) domains of controlled sizes trapped within the PB network were synthesized. To reach that goal, novel (PB(Si(OEt)3)-b-PEO)3 star block copolymers were designed by hydrosilylation of the pendant double bonds of (PB-b-PEO)3 star block copolymer precursors with triethoxysilane. The (PB(Si(OEt)3)-b-PEO)3 star block copolymers were characterized by 1H NMR and IR spectroscopy. Self-condensation of the triethoxysilane pendant groups under acidic conditions led to a successful cross-linking of the polybutadiene blocks directly at the air/water interface without any additives or reagents. This strategy was found more efficient than radical cross-linking of (PB-b-PEO)3 with AIBN to get a homogeneously cross-linked monolayer of controlled and fixed morphology as demonstrated by the easy mechanical removal of the cross-linked Langmuir film from the water surface. As shown by AFM imaging, this strategy allows the accurate control of the PEO "pore" size depending on the monolayer surface pressure applied during the cross-linking reaction. The subphase pH and surface pressure influence on the cross-linking kinetics and monolayer morphologies were investigated by Langmuir trough studies (isotherm and isobar experiments) and AFM imaging.     

First synthesis of picealactone C. A new route toward taxodione-related terpenoids from abietic acid

A new route to 12-hydroxyabietic acid (10) and related compounds from abietic acid (12), via acetoxyalcohol 15, is reported. Utilizing this, the first synthesis of picealactone C (5) was achieved. The synthesis of natural 12-hydroxydehydroabietic acid (8), 18-hydroxyferruginol (9) and methyl 12α-hydroxyabietate (11) is also reported.     

Thermo sensitive behavior of cellulose derivatives in dilute aqueous solutions: from macroscopic to mesoscopic scale

Thermal behaviors of thermo sensitive hydroxypropyl cellulose (HPC), methyl cellulose (MC) and methyl hydroxypropyl cellulose (MHPC) solutions have been investigated in dilute regime of concentration (C相似文献   

Random Polyesteramides Based on Glycolic Acid and β-Alanine

A series of random polyesteramides (PEAs) within a range of molar composition from 90/10 to 10/90 were synthesized by a direct melt polycondensation of glycolic acid and β-alanine. Their structures were fully characterized by NMR spectroscopy. The resulting copolymers are amorphous and present increasing glass transition temperatures at increasing β-alanine contents. The copolymers were also characterized by, FTIR, TGA and viscosimetry measurements.