Morphology-dependent electrochemistry of FeOOH nanostructures

Four kinds of iron hydroxide (FeOOH) structures with the morphologies of bulk, nano-sheet, nano-sphere, and nano-rod were synthesized using solvothermal processes. During synthesis different reagents were added to tune the morphology of FeOOH structures. These structures were characterized using TEM and SEM as well as from their Raman and XPS spectra. Voltammetric response of these structures as well as redox probes and endocrine disrupting compounds (EDCs) on these structures based electrodes was investigated. The morphology-dependent electrochemistry of these FeOOH structures was found. The highest redox activity of FeOOH was achieved on the FeOOH nano-rod structure based electrode, which was the best interface as well for the electrochemistry of both redox probes and EDCs. On such an interface, the highest magnitudes of both diethylstilbestrol (DES) and bisphenol A (BPA) were obtained.     

Numerical simulation of indoor suspension particles based on v-f model

This paper presents a new algorithm for the prediction of indoor suspension particle dispersion based on a v²-f model. In order to handle the near-wall turbulence anisotropy properly, which is significant in the dispersion of fine particles, the particle eddy diffusivity is calculated using different formulae among regions of the turbulent core and in the vicinity of walls. The new algorithm is validated by several cases performed in two ventilated rooms with various air distribution patterns. The simulation results reveal that v²-f nonlinear turbulence model combined with a particle convective equation gives satisfactory agreement with the experimental data. It is generally found that the dynamic equation combined with the v²-f model can properly handle low Reynolds number (LRN) flows which are usually encountered in indoor air flows and fine particle dispersion.     

Influence of switchable magnetic field on the modulation property of nanostructured magnetic fluids

Magnetic fluid is a kind of colloidal material with tunable microstructure and unique optical properties. The tunable magneto-optical modulation property of magnetic fluid under externally switchable magnetic field with various modulation periods is investigated theoretically and experimentally. The transitional modulation period (lower limit of the working frequency) between the square-like and oscillation-like modulation is achieved and found to be magnetic-field- and sample-concentration-dependent. The modulation mechanism is analyzed and ascribed to the dynamic microstructure of magnetic fluid under different modulation periods of external magnetic fields. The result of this work may be helpful for the pragmatic applications of magnetic fluid based on the square-like modulation.     

MPM simulations of high-speed machining of Ti6Al4V titanium alloy considering dynamic recrystallization phenomenon and thermal conductivity

Ti6Al4V titanium alloy is often used in the aircraft industry due to its good strength and toughness etc. However, it is very difficult to simulate high speed machining of titanium alloy using the finite element method (FEM). The reason is that the high speed, large deformation and high strain rate of metal material at high temperature etc. will lead to the element distortions and other numerical difficulties. In contrast with FEM, material point method (MPM) has the advantage of simulating extreme large deformation, fracture and impact problems. Therefore, it is specially suitable for dealing with high speed cutting process. In many existing researches about the high speed cutting process using Johnson−Cook constitutive model, the material dynamic recrystallization softening effect under high pressure and high temperature has not been considered. For this, three modified Johnson−Cook constitutive models for Ti6Al4V titanium alloy are adopted and the parameters for these models were obtained by the split Hopkinson pressure bar (SHPB) test considering the critical strain values, high-temperature range and dynamic recrystallization phenomenon. Furthermore, to ensure the numerical accuracy, the transient heat conduction algorithm is employed in MPM implementation. Finally, comparison and discussion are carried out between the experimental and the simulation data, which show that the high speed cutting process can be better simulated using the modified Johnson−Cook constitutive models.     

Coherent electron transport in a helical nanotube

The quantum dynamics of carriers bound to helical tube surfaces is investigated in a thin-layer quantization scheme. By numerically solving the open-boundary Schrödinger equation in curvilinear coordinates, geometric effect on the coherent transmission spectra is analysed in the case of single propagating mode as well as multimode. It is shown that, the coiling endows the helical nanotube with different transport properties from a bent cylindrical surface. Fano resonance appears as a purely geometric effect in the conductance, the corresponding energy of quasibound state is obviously influenced by the torsion and length of the nanotube. We also find new plateaus in the conductance. The transport of double-degenerate mode in this geometry is reminiscent of the Zeeman coupling between the magnetic field and spin angular momentum in quasi-one-dimensional structure.     

Development of a Novel Process of Corrosion Rate Estimation of Steel under Stray Current Interference: Q235A Pipe Steel as an Example

Russian Journal of Electrochemistry - With the progress of urbanization, stray current corrosion has attracted numerous attention due to its safety threaten to buried metallic pipelines around the...     

A three‐dimensional Cartesian cut cell method for incompressible viscous flow with irregular domains

A three‐dimensional Cartesion cut cell method is presented for the simulations of incompressible viscous flows with irregular domains. A new model (referred to as ‘6+N’ model) is proposed to describe arbitrarily shaped cut cells and treat all the cells as polyhedrons with 6+N faces. The finite volume discretization of the Navier–Stokes equation is then implemented by using the ‘6+N’ model to separate the surface flux integrals into two parts, that is, the fluxes through the basic face of the hexahedron and those through the cutting surfaces. The previously proposed Kitta Cube algorithm and volume computer‐aided design platform (J. Comput. Aided. Des. 2005; 37(4): 1509–1520. Doi:10.1016/j.cad.2005.03.006) are adopted to generate cut cells and provide shape data and physical attributes for the numerical analysis. A modified SIMPLE‐based smoothing pressure correction scheme is applied to suppress checkerboard pressure oscillations caused by the collocated arrangement of velocities and pressure. The calculation accuracy of the numerical method expressed by L₁ and L _∞ norm errors is first demonstrated by the simulation of a pipe flow. Then its feasibility, efficiency, and potential in engineering applications are verified by applying it to solve natural convections between concentric spheres and between eccentric spheres. The heat transfer patterns in eccentric spheres are also obtained by using the numerical method. Copyright © 2011 John Wiley & Sons, Ltd.     

Structural recovery mechanism after shear induced orientation of multiwalled carbon nanotube in polypropylene matrix

In this work the flow induced orientation and the governing mechanism of structural recovery of multi-walled carbon nanotube (MWCNT) filled polypropylene nanocomposites were investigated. A series of linear and nonlinear melt rheological measurements including stress growth and time sweep experiments were performed at different temperatures to study the structural breakdown, nanoparticles orientation, subsequent structural recovery and MWCNT loadings. The results showed that the structural recovery occurred in two stages. The first stage, initial agglomeration, showed a quick recovery which was independent of temperature, can be interpreted in terms of inter-particle van der Waals interactions. This structural recovery stage had major contribution in the storage modulus increment. The second stage of the recovery, secondary agglomeration, was slower and dependent on temperature, can be attributed to rotary diffusion of nanoparticles. This stage had minor contribution to the storage modulus increase. Storage modulus increment in both of these agglomeration was attributed to the increase of nanotube-nanotube contacts. Both of these stages were confirmed by transmission electron micrographs. These result were in a good agreement with those calculated using van der Waals and diffusion concepts.     

A generator of families of two-step numerical methods with free parameters and minimal phase-lag

This research work is oriented in the behaviour of oscillating systems. In order to study such problems, we deal with the solution of ordinary second order differential equations. A generator of families of numerical methods is developed in our effort to solve equations of that type. The families created have constant coefficients and free parameters. We calculate the free parameters taking into consideration the condition of minimal phase-lag. The new methods are applied to the problem of the time independent Schrödinger equation and their results are presented. We also examine the properties of stability and minimum local truncation error.     

Calculation of Bayes premium for conditional elliptical risks

In this paper we discuss the calculation of the Bayes premium for conditionally elliptical multivariate risks. In our framework the prior distribution is allowed to be very general requiring only that its probability density function satisfies some smoothness conditions. Based on the previous results of Landsman and Nešlehová (2008) and Hamada and Valdez (2008) we show in this paper that for conditionally multivariate elliptical risks the calculation of the Bayes premium is closely related to the Brown identity and the celebrated Stein’s lemma.