Application of continual injection liquid‐phase microextraction method coupled with liquid chromatography to the analysis of organophosphorus pesticides

A liquid‐phase microextraction coupled with LC method has been developed for the determination of organophosphorus pesticides (methidation, quinalphos and profenofos) in drinking water samples. In this method, a small amount (3 μL) of isooctane as the acceptor phase was introduced continually to fill‐up the channel of a 1.5 cm polypropylene hollow fiber using a microsyringe while the hollow fiber was immersed in an aqueous donor solution. A portion of the acceptor phase (ca. 0.4 μL) was first introduced into the hollow fiber and additional amounts (ca. 0.2 μL) of the acceptor phase were introduced to replenish at intervals of 3 min until set end of extraction (40 min). After extraction, the acceptor phase was withdrawn and transferred into a 2 mL vial for a drying step prior to injection into a LC system. Parameters that affect the extraction efficiency were studied including the organic solvent, length of fiber, volume of acceptor and donor phase, stirring rate, extraction time, and effect of salting out. The proposed method provided good enrichment factors of up to 189.50, with RSD ranging from 0.10 to 0.29%, analyte recoveries of over 79.80% and good linearity ranging from 10.0 to 1.25 mg/L. The LOD ranged from 2.86 to 82.66 μg/L. This method was applied successfully to the determination of organophosphorus pesticides in selected drinking water samples.     

Robust stability analysis of static neural network with S-type distributed delays

In this paper, we investigate local robust stability of static neural network (SNN) with S-type distributed delays. We derive some new sufficient conditions for local robust stability of equilibrium points and estimate attracting domains of equilibrium points except isolated equilibrium points. Our results not only show local robust stability of equilibrium points but also allow much broader application for static neural network with or without delays. It is shown that our results are new and improve corresponding results existing in the previous literature.     

Stability of singularly perturbed switched systems with time delay and impulsive effects

This paper studies the stability properties of singularly perturbed switched systems with time delay and impulsive effects. Such systems are assumed to consist of both unstable and stable subsystems. By using the multiple Lyapunov functions technique and the dwell time approach, some stability criteria are established. Our results show that impulses do contribute in order to obtain stability properties even when the system consists of only unstable subsystems. Numerical examples are presented to verify our theoretical results.     

Exponential stability preservation in semi-discretisations of BAM networks with nonlinear impulses

This paper demonstrates the reliability of a discrete-time analogue in preserving the exponential convergence of a bidirectional associative memory (BAM) network that is subject to nonlinear impulses. The analogue derived from a semi-discretisation technique with the value of the time-step fixed is treated as a discrete-time dynamical system while its exponential convergence towards an equilibrium state is studied. Thereby, a family of sufficiency conditions governing the network parameters and the impulse magnitude and frequency is obtained for the convergence. As special cases, one can obtain from our results, those corresponding to the non-impulsive discrete-time BAM networks and also those corresponding to continuous-time (impulsive and non-impulsive) systems. A relation between the Lyapunov exponent of the non-impulsive system and that of the impulsive system involving the size of the impulses and the inter-impulse intervals is obtained.     

Enhanced skin permeation of salicylate by ion-pair formation in non-aqueous vehicle and further enhancement by ethanol and l-menthol

Enhancement of skin permeability of salicylate from non-aqueous vehicle by ion-pair formation with either alkylamines or benzylamine as model cationic ions was examined in excised guinea pig dorsal skin. Solubility of salicylate in isopropyl myristate (IPM) was increased by the addition of either alkylamines or benzylamine as counter ions. The increase was more significant in the presence of amines with longer alkyl chains. Flux of salicylate increased in the presence of these amines due to the increase in the solubility. Maximum flux was observed in the presence of n-hexylamine, which induced an 11-fold increase due to 137-fold increase in solubility. Flux and permeability coefficients of salicylate in the presence of n-butylamine, n-hexylamine, iso-octylamine and benzylamine as counter ions in IPM were larger than those of the non-ionic form of salicylic acid. Flux of 3-methylsalicylate (3-CH3 substituent) and that of 5-hydroxysalicylate (5-OH substituent) were smaller than that of salicylate in the presence of n-hexylamine. After partition to the skin surface, the ion-pair is suggested to dissociate and permeate separately according to the study using lidocaine as the counter ion. Flux of salicylate increased in the presence of benzylamine as the counter ion by the addition of 15% ethanol and 15% ethanol plus 1% l-menthol due to further improvement in the solubility as well as an increase in the permeability coefficient.     

A mild and regioselective method for alpha-bromination of beta-keto esters and 1,3-diketones using bromodimethylsulfonium bromide (BDMS)

Bromodimethylsulfonium bromide has been found to be an effective and regioselective reagent for alpha-monobromination of beta-keto esters and 1,3-diketones. A wide variety of beta-keto esters and 1,3-diketones undergo chemoselective alpha-monobromination with excellent yields at 0-5 degrees C or room temperature. The notable advantages of this protocol are no need of chromatographic separation, use of less hazardous reagent than molecular bromine, and no added base, Lewis acid, or other catalyst.     

Low temperature adsorption of oxygen on reduced V2O3(0 0 0 1) surfaces

Well ordered V₂O₃(0 0 0 1) films were prepared on Au(1 1 1) and W(1 1 0) substrates. These films are terminated by a layer of vanadyl groups under typical UHV conditions. Reduction by electron bombardment may remove the oxygen atoms of the vanadyl layer, leading to a surface terminated by vanadium atoms. The interaction of oxygen with the reduced V₂O₃(0 0 0 1) surface has been studied in the temperature range from 80 to 610 K. Thermal desorption spectroscopy (TDS), infrared reflection absorption spectroscopy (IRAS), high resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) were used to study the adsorbed oxygen species. Low temperature adsorption of oxygen on reduced V₂O₃(0 0 0 1) occurs both dissociatively and molecularly. At 90 K a negatively charged molecular oxygen species is observed. Upon annealing the adsorbed oxygen species dissociates, re-oxidizing the reduced surface by the formation of vanadyl species. Density functional theory was employed to calculate the structure and the vibrational frequencies of the O₂ species on the surface. Using both cluster and periodic models, the surface species could be identified as η²-peroxo () lying flat on surface, bonded to the surface vanadium atoms. Although the O-O vibrational normal mode involves motions almost parallel to the surface, it can be detected by infrared spectroscopy because it is connected with a change of the dipole moment perpendicular to the surface.     

Performance of Rubberized and Hybrid Rubberized Concrete Structures under Static and Impact Load Conditions

In this study, rubberized concrete samples were prepared by partial substitution (5 %, 10 % and 20 % replacements by volume) of sand by waste crumb rubber, and tested under impact three-point bending load, as well as static load. Three types of specimens (size 50?×?100?×?500 mm) namely, plain concrete, rubberized concrete, and double layer concrete (with rubberized concrete top and plain concrete bottom) were loaded to failure in a drop-weight impact machine by subjecting to 20 N weight from a height of 300 mm, and another three similar specimens were used for the static load test. In both the tests, the load–displacement and fracture energy of each specimen were investigated. Finite-element simulations were also performed to study the dynamic behaviors of the samples, by using LUSAS V.14 software. It was noticed that, the impact tup, and inertial and bending loads increased with the increase in the percentage of sand replacement by crumb rubber. It was interesting to observe that these effects were more significant in the double layer specimen compared to the plain and rubberized concrete samples. The static peak bending load always decreased with increase of rubber in the mix. In general, the strength and energy absorbing capability of rubberized concrete was better under impact loading than under static loading. The simulated load against displacement behaviors of all the samples were validated by the experimental results.     

Overlap of Doxycycline Fluorescence with that of the Redox-Sensitive Intracellular Reporter roGFP

Tetracycline-inducible systems allow for either suppression or induction of transgene expression to facilitate studies of cell physiology. Doxycycline is a preferred inducer for these gene expression systems due to its membrane permeability; however, the heterocyclic structure of doxycycline exhibits fluorogenic properties that can potentially bias measurement of other fluorochromes. Thus the simultaneous use of tetracycline-inducible systems and fluorescent proteins as reporter genes or as intracellular biosensors may lead to potentially confounding results. Herein, using cells which co-express the ratiometric redox sensitive intracellular reporter, roGFP, and a tetracycline-inducible reporter plasmid encoding the reporter gene, mCherry, as a model system, we describe the overlapping intracellular fluorescent signals between doxycycline and commonly used intracellular fluorescent probes. In our cells, the addition of doxycycline to cells caused a dose- and time-dependent increase in cell fluorescence with 405 nm excitation which overlapped with that of the oxidized configuration of roGFP. Incubating cells in concentrations of doxycycline less than 1 μg/mL and removing doxycycline from the media 60 min before performing experiments eliminated fluorescence interference while still maintaining maximal reporter transgene activation.