Measurement of the thermal conductivity of MWCNT-CuO/water hybrid nanofluid using artificial neural networks (ANNs)

Journal of Thermal Analysis and Calorimetry - In this paper, artificial neural networks (ANNs) are developed to predict the thermal conductivity ( $$k_{\text{nf}}$$ ) of multi-walled carbon...     

Electrochemical oxidation of some catechol derivatives in the presence of some betadicetone derivatives: mechanistic and thermodynamic study

Electrochemical oxidations of 4-methylcatechol (1), 4-tert-butylcatechol (5) and catechol (7) in the presence of different nucleophiles have been investigated both experimentally and theoretically. Experimental results have been obtained by means of cyclic voltammetry and controlled-potential coulometry. Also the theoretical results were calculated at DFT (B3LYP) level of theory and 6–311+G (p, d) basis set. The calculated results indicate that oxidation potential of catechols (1, 5, 7) and their substituted species are directly dependent on the ?G _tot, and continuance of reactions during electrolysis is dependent on ?G _tot of produced species on the surface of electrode. The current study indicates that theoretical studies along with empirical research can be useful in displaying electrochemical reaction mechanisms.     

An adaptive algorithm for solving stochastic multi-point boundary value problems

In this paper, we present an adaptive multiple-shooting method to solve stochastic multi-point boundary value problems. We first analyze the strong order of convergence of the underlying multiple shooting method. We then proceed to describe the proposed strategy to adaptively choose the location of shooting points. We analyze the effect of method parameters on the performance of the overall scheme using a benchmark linear two-point stochastic boundary value problem. We illustrate the effectiveness of this approach on several (one and two dimensional) test problems by comparing our results with other non-adaptive alternative techniques proposed in the literature.     

A molecularly imprinted polymer based on multiwalled carbon nanotubes for separation and spectrophotometric determination of L-cysteine

The authors describe a molecularly imprinted polymer (MIP) deposited on multiwalled carbon nanotubes (MIP/MWCNTs) for separation and preconcentration of L-cysteine (L-Cys). The MIP was characterized by scanning electron microscopy, X-ray diffraction and FT-IR and via adsorption kinetics and adsorption isotherms. The MIP is shown to be a viable sorbent for L-Cys which subsequently is quantified by spectrophotometry through formation of a charge transfer complex with the DDQ reagent. The experimental parameters affecting separation efficiency and spectrophotometric determination were optimized. Under optimum conditions and at an analytical wavelength of 478 nm, the calibration plot is linear in the 4.0 to 180 ng mL^?1 concentration range, and the limit of detection (at an S/N ratio of 3) is 2.3 ng mL^?1. The intra-day and inter-day precision are in the range from 2.4 to 3.6%. The method was successfully applied to determination of L-Cys in spiked human serum and water samples where it gave recoveries ranging from 96.6 to 102.4%.

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Graphical abstract Schematic of the preparation of a  molecularly imprinted polymer coated on the multiwalled carbon nanotube (MIP/MWCNT) by functionalization of MCNTs with methacrylic acid and subsequent polymerization. The MIP/MWCNTs were successfully applied for extraction and spectrophotometric determination of L-Cys by charge transfer (CT) complexation.

     

Exploring the impacts of the vinylogous anomeric effect on the synchronous early and late transition states of the hydrogen molecule elimination reactions of cis-3,6-dihalocyclohexa-1,4-dienes

LC-ωPBE, B3LYP, and M06-2X methods with the 6–311+G** basis set on all atoms and natural bond orbital (NBO) interpretation were performed to investigate the roles and contributions of the effective factors on the potential energy surfaces of the hydrogen molecule elimination reactions of cyclohexa-1,4-diene (1) and its cis-3,6-dihalo derivatives [halogen=F (2), Cl (3), Br (4)] to hydrogen molecule and their corresponding aromatic rings. The ring puckering in compound 2 (which results from the repulsive electrostatic interactions between the natural bond orbital dipole moments of two C-F bonds) shortens the allylic hydrogen atoms’ distance, leading to the smaller barrier height in compound 2 compared to that in compound 1. The barrier heights of the hydrogen molecule elimination reactions increase from compounds 2 to 4 while their corresponding exothermic characters decrease. The variations of the advancements of transition state structures (δB _av) reveal that the hydrogen molecule elimination reactions of compounds 2–4 do not obey the Hammond-Leffler postulate. In compound 2, the ring puckering shortens the allylic hydrogen distance (d _H8-H10) while d _H8-H10 values increase going from compounds 2 to 4, leading to the increase of their corresponding hydrogen molecule elimination reactions barrier heights. Interestingly, the variations of the vinylogous hyperconjugative anomeric effects justify the directions of the rings puckering going from compounds 2 to 4. The increase of the activation exchange components [PETR _(TS)-PETR _(GS)] going from compounds 2 to 4 correlates well with their corresponding hydrogen molecule elimination process barrier heights.     

Solid-phase microextraction of chlorpyrifos in fruit samples by synthesised monolithic molecularly imprinted polymer fibres

A monolithic solid-phase microextraction (SPME) fibre was fabricated based on a molecularly imprinted polymer that could be coupled with gas chromatography for extraction, and determination of chlorpyrifos. The time of extraction, pH, temperature and ionic strength were investigated as important factors on the extraction procedure. The fabricated fibre was firm, inexpensive, stable and selective which gave it vital importance in SPME. The selectivity of the fabricated fibre in relation to analogue compounds was also investigated. Under the optimum conditions, the calibration curve was linear in the range of 1–20 mg L^?1 (R² = 0.9899). The high extraction efficiency was obtained for chlorpyrifos with a detection limit of 0.23 mg L^?1. The fabricated fibre was successfully applied to SPME of chlorpyrifos from apple and grape fruits after its extraction and followed by gas chromatography-flame ionisation detector analysis.     

Phase space analysis of interacting dark energy in f(T) cosmology

In this paper, we examine the interacting dark energy model in f(T) cosmology. We assume dark energy as a perfect fluid and choose a specific cosmologically viable form f(T) = ????T. We show that there is one attractor solution to the dynamical equation of f(T) Friedmann equations. Further we investigate the stability in phase space for a general f(T) model with two interacting fluids. By studying the local stability near the critical points, we show that the critical points lie on the sheet u* = (c ? 1)v* in the phase space, spanned by coordinates (u, v, ??, T). From this critical sheet, we conclude that the coupling between the dark energy and matter c ?? (?2, 0).     

Numerical simulation of dielectric bubbles coalescence under the effects of uniform magnetic field

In this research, the co-axial coalescence of a pair of gas bubbles rising in a viscous liquid column under the effects of an external uniform magnetic field is simulated numerically. Considered fluids are dielectric, and applied magnetic field is uniform. Effects of different strengths of magnetic field on the interaction of in-line rising bubbles and coalescence between them were investigated. For numerical modeling of the problem, a computer code was developed to solve the governing equations which are continuity, Navier–Stokes equation, magnetic field equation and level set and reinitialization of level set equations. The finite volume method is used for the discretization of the continuity and momentum equations using SIMPLE scheme where the finite difference method is used to discretization of the magnetic field equations. Also a level set method is used to capture the interface of two phases. The results are compared with available numerical and experimental results in the case of no-magnetic field effect which show a good agreement. It is found that uniform magnetic field accelerates the coalescence of the bubbles in dielectric fluids and enhances the rise velocity of the coalesced bubble.     

DFT Study of Adsorption of Diazinon,Hinosan, Chlorpyrifos and Parathion Pesticides on the Surface of B36N36 Nanocage and Its Fe Doped Derivatives as New Adsorbents

In this work, we used density functional theory with the Tkatchenko and Scheffler method to investigate the adsorption of diazinon, hinosan, chlorpyrifos, and parathion organophosphorus pesticides on the surface of B₃₆N₃₆ nanocage and its Fe doped derivatives. The assessments revealed that van der Waals interaction is a key factor in organophosphate adsorption on the surface of these nanocages as well as overlapping. The results of Fukui indices and atomic partial charges calculations indicated that these pesticides and nanocages act as nucleophile and electrophile, respectively, and the adsorption sites of all four organophosphates on these nanocages are thiophosphate groups, as well as the aromatic ring in diazinon, and the nitro group in parathion. In addition, the calculated adsorption energies yielded the best result for diazinon, and the best Fe doped B₃₆N₃₆ derivative for adsorbing organophosphates in aqueous solution is the one in which Fe atom is located in the boron position of the square ring of B₃₆N₃₆.     

Thermal performance improvement in water nanofluid/GNP–SDBS in novel design of double-layer microchannel heat sink with sinusoidal cavities and rectangular ribs

In this numerical study, laminar flow of water nanofluid/GNP–SDBS (graphene nanoplatelet–sodium dodecylbenzene sulfonate) for 0–0.1% solid nanoparticles mass fraction was investigated for Reynolds numbers of 50–1000 in 3D space via finite volume method. In the newly proposed microchannel design, the cooling fluid is moving in countercurrent in the upper and lower layers of the microchannels, and there are cavities and sinusoidal routes on the solid walls of the microchannel, and the presence of rectangular ribs on the flow centerline along the fluid path enhances mixing for cooling fluid and creates better heat transfer for warm surfaces. The results of this study show that this special design of the microchannel can have a substantial increase in Nusselt number and heat transfer so that in the considered geometry by adding solid nanoparticles mass fraction it is possible to increase average Nusselt number for each Reynolds number by approximately 20%. Also, the mixing of the fluid because of formation of secondary flows has a strong effect on making the temperature distribution uniform in the cooling fluid and solid bed (wall) of the microchannel, especially in the lower layer. The upper layer of the microchannel always has a lower temperature due to indirect contact with heat flux compared with the lower layer. In this study, by increasing Reynolds number and mass fraction of solid nanoparticles the Nusselt number is increased and heat resistance of the lower wall of the microchannel is reduced. Based on the investigation of flow field and heat transfer, the use of the proposed design of the microchannel is recommended for Reynolds number less than 300.