Impact of hindered Brownian diffusion on the accuracy of particle-image velocimetry using evanescent-wave illumination

The nano-particle image velocimetry technique uses evanescent-wave illumination generated by total internal reflection at the wall to excite colloidal neutrally buoyant fluorescent tracer particles. The displacement of these particles over time as they are convected by the flow then gives the flow velocity components tangential to the wall. Since the extent of the illumination region normal to the wall is comparable to the particle diameter, a major source of error in this technique is particle mismatch within a pair of images due to Brownian diffusion causing a particle to move in to or out of the illuminated region. The brightness (proportional to the amount of imaged fluorescence) and size of individual particle images in nPIV data are discussed. A sequence of artificial nPIV images are generated for a known uniform velocity field with the particles subject to hindered Brownian diffusion. The velocity fields calculated from these artificial images are compared with the known velocity field to determine the effect of Brownian diffusion-induced particle mismatch on nPIV accuracy. A similar analysis is carried out for experimental nPIV images. The results provide design guidance for experimental measurements using the nPIV technique.     

Nano TiO2 Modified Carbon‐ceramic Electrode and Its Application for Electrocatalytic Oxidation of NADH

The electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) was studied on nanoTiO₂ modified sol‐gel electrode, using cyclic voltammetry, chronoamperometry and differential pulse voltammetry as diagnostic techniques. It is demonstrated that TiO₂ nanoparticles on sol‐gel network catalyze the oxidation of NADH in the absence of any electron transfer mediators. Effect of various parameters such as pH, scan rate, TiO₂ percentage on the response of modified electrode was studied. In addition, scanning electron microscopy (SEM) was used to characterize the surface morphology of the spots. A dynamic range between 0.5–50 μM with detection limit of 0.35 μM was obtained with DPV studies. This method was successfully used for determination of NADH in cucumber cotyledons samples. The electrode showed relatively good stability over more than 2 months.     

Facile synthesis of Fe3O4/MoS2 nanohybrid for solid phase extraction of Ag(I) and Pb(II): kinetic,isotherm and thermodynamic studies

Recently, MoS₂ with abundant electron density in its structure attracted more attention as an adsorbent for environmental remediation. However, hard manipulation of target solution owing to high dispersibility in aqueous media restricts its application as adsorbent. Preparation of Fe₃O₄/MoS₂ nanohybrid can solve this problem. Also, this nanohybrid improves adsorption capacities of target ions. In this work, Fe₃O₄ nanoparticles, MoS₂ nanosheets and hybrid of these two were synthesised and then characterised by X-ray diffraction, energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, Fourier transforms infrared spectra, Brunauer–Emmett–Teller surface area and vibrating sample magnetometer. Subsequently, adsorption of Ag(I) and Pb(II) ions from aqueous solution by these three adsorbents was examined in detail and compared with each other while the adsorption conditions including the pH value, contact time, dosage of sorbent, elution conditions and interfering ions have been optimised. According to obtained results, prepared nanohybrid showed enhanced adsorption capacities for both ions relative to naked Fe₃O₄ and MoS₂. The limits of detection for Ag(I) and Pb(II) were calculated as 0.49 µg L^?1 and 2.7 µg L^?1, respectively, and the relative standard deviation percentages (n = 5) for Ag(I) and Pb(II) were 2.8%, and 3.0%, respectively. Furthermore, the preconcentration factors were 300 and 75 for Ag(I) and Pb(II) ions, respectively. Moreover, kinetic studies showed that pseudo-second-order model can better describe target analytes adsorption properties by every three adsorbents. Regeneration of the adsorbents was performed with HCl/thiourea mixture.     

Tungsten hexachloride nanoparticles loaded on montmorillonite K-10: a novel solid acid catalyst in the synthesis of symmetrical and unsymmetrical azines

In the present investigation, we have developed a novel technique to prepare azines using nano-WCl₆ loaded on Montmorillonite K10 clay as a highly active catalyst. A variety of aldehydes and ketones were efficiently converted to the corresponding azines using catalytic amounts of nanosized WCl₆/Mont. K10 under mild conditions. The nanostructures of WCl₆ loaded on Mont. K10 as solid acid catalyst have been prepared by solid dispersion method. The advantages of this catalyst are rapid completion of the reactions, simplicity of performance, lack of pollution and mild and green reaction conditions. The morphologies, structure, and chemical components of parent and modified clay were successfully characterized using SEM, FT-IR, CV, XRD and EDX measurements.     

Catalytic performance in 4-nitrophenol reduction by Ag nanoparticles stabilized on biodegradable amphiphilic copolymers

Biodegradable copolymers have received much more attention in the last decades due their potential applications in the fields related to environmental protection, medicine, agriculture, and the chemical processes. Silver nanoparticles (Ag NPs) were prepared via reduction of silver nitrate (AgNO₃) using biodegradable amphiphilic copolymers in aqueous solution. The micelles were constructed from the amphiphilic copolymer composed of poly(2-ethyl-2-oxazoline) and poly(ε-caprolactone). The Ag NPs with a diameter of 10–15?nm were found to show a comparable high catalytic activity toward the reduction of 4-nitrophenol (4-NP) in the presence of an excess amount of NaBH₄. The synthesized Ag NPs-loaded copolymer exhibits high catalytic activity for the reduction of 4-NP to 4-aminophenol.     

Peristaltic Wave Locomotion and Shape Morphing with a Millipede Inspired System

We present the mechanical model of a bio-inspired deformable system, modeled as a Timoshenko beam, which is coupled to a substrate by a system of distributed elements. The locomotion action is inspired by the coordinated motion of coupling elements that mimic the legs of millipedes and centipedes, whose leg-to-ground contact can be described as a peristaltic displacement wave. The multi-legged structure is crucial in providing redundancy and robustness in the interaction with unstructured environments and terrains. A Lagrangian approach is used to derive the governing equations of the system that couple locomotion and shape morphing. Features and limitations of the model are illustrated with numerical simulations.     

Cohomogeneity one actions on Minkowski spaces

We study isometric cohomogeneity one actions on the \((n+1)\)-dimensional Minkowski space \(\mathbb {L}^{n+1}\) up to orbit-equivalence. We give examples of isometric cohomogeneity one actions on \(\mathbb {L}^{n+1}\) whose orbit spaces are non-Hausdorff. We show that there exist isometric cohomogeneity one actions on \(\mathbb {L}^{n+1}\), \(n \ge 3\), which are orbit-equivalent on the complement of an n-dimensional degenerate subspace \(\mathbb {W}^n\) of \(\mathbb {L}^{n+1}\) and not orbit-equivalent on \(\mathbb {W}^n\). We classify isometric cohomogeneity one actions on \(\mathbb {L}^2\) and \(\mathbb {L}^3\) up to orbit-equivalence.     

Nuclear magnetic resonance study of the stoichiometry and stability of several HgX<Subscript>2</Subscript>–acetylemethylentriparatolylphosphorane complexes in various acetone–dimethylformamide mixtures

The reaction of phosphorus ylide, acetylmethylenetriparatolylphosphorane (L) with HgX₂ (X = Cl, Br, I and NO₃) in equimolar ratios using acetone and dimethylformamide as solvents leads to binuclear products. ³¹P NMR spectroscopy was used to investigate the stoichiometry and stability of a HgX₂ complex with CH₃COCHP(p-tolyl)₃ (L) in binary acetone–dimethylformamide mixtures of varying composition. In all cases studied, the variation of ³¹P NMR chemical shift with the [HgX₂]/[L] mole ratio indicated the formation of 1:1 complexes. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation that relates the observed chemical shifts to the formation constant. In all mercuric salts used, the stabilities of the resulting 1:1 complexes varied in the order Hg(NO₃)₂ > HgCl₂ > HgBr₂ > HgI₂. It was found that, in the case of all complexes, an increase in the percentage of dimethylformamide in the solvent mixtures significantly decreases the stability of the complexes.     

Highly selective oxidation of alcohols using MnO2/TiO2-ZrO2 as a novel heterogeneous catalyst

MnO₂/TiO₂-ZrO₂, which was synthesized by the adsorption method, demonstrated very high catalytic activity in the selective oxidation of benzyl alcohols to benzaldehydes with excellent yields and selectivity in short reaction times. The physical and chemical properties of MnO₂/TiO₂-ZrO₂ were investigated by XRD, XRF, BET, FT-IR and SEM techniques. The influence of the catalyst support (SBA-15, ZSM-5, TiO₂-ZrO₂ and Y), type of metal oxide supported, method of loading and amount of manganese nitrate loading have been thoroughly investigated. Moreover, the catalyst has shown excellent reusability in the process.