Spherical Layer Structure Research Articles

The simultaneous synthesis of carbon dots and carbon spheres with tunable sizes using a vertical chemical vapour deposition method

Herein we report on the direct synthesis of solid hydrophobic carbon dots (CDs) and simultaneously carbon spheres (CSs), using a vertical chemical vapour deposition (CVD) reactor. The HRTEM data indicated that the CDs and CSs originated from different carbon building blocks indicated that the CDs and CSs originated from different carbon building blocks. The CDs were obtained by reacting acetylene (C2H2) and Ar mixtures at high flow rates (>500 sccm) and high temperatures (800-1000 °C). TEM studies indicated that the CDs produced were graphene-like quantum dots that increased in size from c. 3 nm to 8 nm as the Ar flow rate (constant C2H2 flow rate) was decreased, while small solid CSs (c. 100 nm) were also synthesised in the process. The CSs had a typical spherical layered structure with no graphitic core. A mechanism to rationalise the observation that the CDs and CSs grew simultaneously by different pathways with no formation of intermediate-sized particles is given.

Analytical study on shear wave propagation in anisotropic dry sandy spherical layered structure

An analytical study on the propagation characteristics of shear wave in a spherical layered structure comprising of an isotropic sandy material medium covered by a concentric spherical transversely isotropic sandy material layer of finite thickness has been carried out in the present work. The source of excitation for wave propagation is considered in the outer layer and the analytical treatment with contour integration and Fourier-Legendre Expansion theorem is utilized to accomplish closed form of dispersion relation. Further, Debye Asymptotic Expansion analysis is used to deal the complication caused by the inclusion of Bessel's function, Hankel's function and their derivatives in the solution procedure. With help of Debye Asymptotic Expansion analysis, the obtained dispersion relation converts in the form of elementary functions and found to be in well-agreement with pre-established and classical results through the particular cases. Numerical computations are done to illustrate the influence of the affecting parameters (anisotropy, sandiness and radii ratio) on dispersion curves graphically. Moreover, to expose the impact of anisotropy, numerical data of three distinct transversely isotropic materials (Magnesium, Zinc and Beryl) are taken into the account to establish the comparative study with isotropic material which serves the major highlights of the present study.

Novel highly dispersed Ni-based oxides catalysts for ethanol steam reforming

To prepare high-performance Ethanol Steam Reforming (ESR) catalyst, copper and magnesium were added into NiAl Layered Double Hydroxides (NiAl-LDHs) employing the coprecipitation method as the second and third metals for reducing the sintering of nickel active components and controlling the acid sites. Afterward, NiCuMgAl-LDHs were wrapped on the SiO2 nanospheres to form a spherical layered structure. The results showed that, compared with the NiAl catalyst, after adding Cu metal, resulting from the synergistic effect of Ni–Cu, the ethanol conversion rate increased at different temperature ranges, and ethanol could be wholly converted at 500 °C. With the addition of Mg for neutralize the acid sites of the catalyst, no ethylene, ethanol dehydration product, was produced over the entire reaction temperature range (350–600 °C). NiCuMgAl-LDHs grows vertically on the surface of SiO2 because its hierarchical layered structure is beneficial to inhibit the collapse of laminates, which makes the active components of Ni on SiO2@NiCuMgAl more dispersed and exists edge and corner sites with few coordinative unsaturated active sites, thus exposing of active components and then enhanced performance. Finally, through the catalyst composition and structure optimization, the ethanol was converted entirely, and the stable hydrogen production was realized in the 19 h test.

Electrical impedance tomography in anisotropic media with known eigenvectors

Electrical impedance tomography is an imaging method, with which volumetric images of conductivity are produced by injecting electrical current and measuring boundary voltages. It has the potential to become a portable non-invasive medical imaging technique. Until now, most implementations have neglected anisotropy even though human tissues like bone, muscle and brain white matter are markedly anisotropic. The recovery of an anisotropic conductivity tensor is uniquely determined by boundary measurements only up to a diffeomorphism that fixes the boundary. Nevertheless, uniqueness can be restored by providing information about the diffeomorphism. There are uniqueness results for two constraints: one eigenvalue and a multiple scalar of a general tensor. A useable constraint for medical applications is when the eigenvectors of the underlying tissue are known, which can be approximated from MRI or estimated from DT-MRI, although the eigenvalues are unknown. However there is no known theoretical result guaranteeing uniqueness for this constraint. In fact, only a few previous inversion studies have attempted to recover one or more eigenvalues assuming certain symmetries while ignoring nonuniqueness. In this work, the aim was to undertake a numerical study of the feasibility of the recovery of a piecewise linear finite element conductivity tensor in anisotropic media with known eigenvectors from the complete boundary data. The work suggests that uniqueness holds for this constraint, in addition to proposing a methodology for the incorporation of this prior for general conductivity tensors. This was carried out by performing an analysis of the Jacobian rank and by reconstructing four conductivity distributions: two diagonal tensors whose eigenvalues were linear and sinusoidal functions, and two general tensors whose eigenvectors resembled physiological tissue, one with eigenvectors spherically orientated like a spherical layered structure, and a sample of DT-MRI data of brain white matter. The Jacobian with respect to three eigenvalues was full-rank and it was possible to recover three eigenvalues for the four simulated distributions. This encourages further theoretical study of the uniqueness for this constraint and supports the use of this as a relevant usable method for medical applications.

Improved calcined clay with a spherical layered structure and its characteristics as a medium for plant growth

This study was conducted to develop an artificial soil substitute for existing growing media such as cocopeat and peatmoss. Minerals such as perlite, zeolite, kaolin, illite and silica were chosen as starting materials. Perlite–zeolite–silica–clay composite granules in different compositions were fabricated using the total mixing method and the layered structure method, and their chemical and physical properties, namely, pH, CEC, EC, EAW and WBC, were compared. The sample with a spherical layered structure displayed pH values that were 0.3–0.6 lower in all the pH ranges studied and had higher CECs of 40–41 cmol +/kg at a calcination temperature of 1000 °C than those using the total mixing method. To meet the Korean average pH values of 5.7–6.3 for growing media, FeS 2 was tested as a calcination additive to lower the pH of the sample. An addition of 1 wt.% FeS 2 could lower the pH from 7.3 to the 5.5–7.0 range, depending on the calcined temperature. Improved calcined clay with a spherical layered structure was fabricated under optimum conditions. The clay had sufficient chemical and physical properties, i.e., a pH of 5.8–6.3, a CEC of 38.2–41.0 cmol +/kg, an EC of 0.18–0.20 dS/m, an EAW of 12.32–30.89, a WBC of 3.14–15.75, and a bulk density of 1.01–1.08 g/cm 3. We conclude that this improved calcined clay with a layered structure can replace organic growing media such as cocopeat and peatmoss by a simple high-shear granulation process.

Simulation of monochromatic and pulse electromagnetic fields in a spherical layered structure

Rigorous analytic methods of electromagnetics are applied to develop a mathematical model for calculation of monochromatic and pulse electromagnetic fields in a sphere enclosed in a shell with arbitrary permittivity and permeability. The influence of the shell and of the position of the reception point located in a spherical single-layer structure on the transmitted pulse electromagnetic field is investigated numerically. Possible applications of the proposed model are indicated.

Complete photonic bandgaps in the visible range from spherical layer structures in dichromate gelatin emulsions

We have fabricated spherical layer structures that exhibit complete photonic bandgaps in the visible range in dichromate gelatin emulsions by holographic interference. The complete bandgap was not a result of the high dielectric contrast but was due to the fact that the spherical layer structure was isotropic with equal spacing in all accessible directions. Angular dependence spectral measurements of the spherical layer structures were in good agreement with the expected results from an ideal structure of dielectric concentric spherical shells with equal spacing. Our fabrication technique and results could pave the way for new applications using complete bandgap photonic crystals.

Precipitated iron Fischer-Tropsch catalyst: Effect of carbidization on the morphology of iron oxyhydroxide nanoneedles

The effect of carbidization on the morphology of iron oxyhydroxide particles has been studied. Homogeneous oxidation of iron(II) sulfate results in predominantly γ-FeOOH particles which have a rod-shaped crystalline structure. Carbidization of the prepared iron oxyhydroxide particles at 270 °C and atmospheric pressure without mechanical stirring was found to produce iron carbides with spherical layered structure residing in close proximity. HRTEM, EDS and electron microdiffraction analysis revealed that carbidization alters the initial nanoneedle-type morphology and generates ultrafine carbide particles with irregular spherical shape. When carbidization was performed under severe mechanical stirring, formation of spherical carbide particles completely separated from each other was obsrved. Initial activity of iron oxyhydroxide for Fischer-Tropsch synthesis was found to be high (a CO conversion of about 84%) which declined steadily with synthesis time (26% CO conversion after 340 h of synthesis). The effect of carbidation on the morphology of iron hydroxide oxide (γ-FeOOH) particles with a three dimensional crystalline nanoneedle structure has studied. Carbidation of γ-FeOOH with CO at atmospheric pressure produced iron carbides with spherical layered structure. HRTEM and EDS analysis revealed that carbidation changes the initial nanoneedles morphology and generates ultrafine carbide particles with irregular spherical shape.

Solving the Problem of Exciting a Spherical-Layer Structure by Radial Currents

Solving the Problem of Exciting a Spherical-Layer Structure by Radial Currents

Stresses in soils under a foundation

An analytical study on the propagation characteristics of shear wave in a spherical layered structure comprising of an isotropic sandy material medium covered by a concentric spherical transversely isotropic sandy material layer of finite thickness has been carried out in the present work. The source of excitation for wave propagation is considered in the outer layer and the analytical treatment with contour integration and Fourier-Legendre Expansion theorem is utilized to accomplish closed form of dispersion relation. Further, Debye Asymptotic Expansion analysis is used to deal the complication caused by the inclusion of Bessel's function, Hankel's function and their derivatives in the solution procedure. With help of Debye Asymptotic Expansion analysis, the obtained dispersion relation converts in the form of elementary functions and found to be in well-agreement with pre-established and classical results through the particular cases. Numerical computations are done to illustrate the influence of the affecting parameters (anisotropy, sandiness and radii ratio) on dispersion curves graphically. Moreover, to expose the impact of anisotropy, numerical data of three distinct transversely isotropic materials (Magnesium, Zinc and Beryl) are taken into the account to establish the comparative study with isotropic material which serves the major highlights of the present study.