The effect of mass transfer on electrochemical impedance of a solid oxide fuel cell anode

This paper presents electrochemical impedance simulation of a solid oxide fuel cell (SOFC) anode in order to investigate the effect of mass transport processes on the impedance spectra. The current model takes in to account the gas-phase transport processes both in the gas channel and within the porous electrode and couples the gas transport processes with the electrochemical kinetics. The impedance simulation is carried out in time domain, and the correlation between the anode harmonic responses to the sinusoidal excitation and the impedance spectra is analyzed. In order to solve the system of non-linear equations, an in-house code based on the finite difference method is developed and utilized. Results show a depressed semicircle in the Nyquist plot, which originates from gas transport processes in the gas channel, in addition to a Warburg diffusion impedance originates from gas transport in the thick porous anode. The influence of parameters such as electrode thickness, inlet gas composition, and temperature is also investigated and the results are discussed. The simulation results are in good agreement with published data.     

An exploration in acoustic radiation force experienced by cylindrical shells via resonance scattering theory

In nonlinear acoustic regime, a body insonified by a sound field is known to experience a steady force that is called the acoustic radiation force (RF). This force is a second-order quantity of the velocity potential function of the ambient medium. Exploiting the sufficiency of linear solution representation of potential function in RF formulation, and following the classical resonance scattering theorem (RST) which suggests the scattered field as a superposition of the resonant field and a background (non-resonant) component, we will show that the radiation force is a composition of three components: background part, resonant part and their interaction. Due to the nonlinearity effects, each part contains the contribution of pure partial waves in addition to their mutual interaction. The numerical results propose the residue component (i.e., subtraction of the background component from the RF) as a good indicator of the contribution of circumferential surface waves in RF. Defining the modal series of radiation force function and its components, it will be shown that within each partial wave, the resonance contribution can be synthesized as the Breit-Wigner form for adequately none-close resonant frequencies. The proposed formulation may be helpful essentially due to its inherent value as a canonical subject in physical acoustics. Furthermore, it may make a tunnel through the circumferential resonance reducing effects on radiation forces.     

Identification of Iwan distribution density function in frictional contacts

Mechanical contacts affect structural responses, causing localized nonlinear variations in the stiffness and damping. The physical behaviors of contact interfaces are quite complicated and almost impossible to model at the micro-scale. In order to establish a meaningful understanding of the friction effects and to predict the contact behavior, a robust parametric friction model is usually employed. This paper employs an Iwan-type model to predict the nonlinear effects of a frictional contact interface. The Iwan model is characterized by its distribution density function which is commonly identified by double differentiation of the experimentally obtained joint interface restoring force. Direct measurement of restoring forces at the contact interface is impractical and estimating it using an inverse approach introduces considerable uncertainties in identification of the density function. This paper develops a more reliable procedure in identification of the Iwan model by relating the density function to the joint interface dissipated energy. The energy dissipated in a contact interface is easily obtained from measurement and it is shown that the dissipation is uniquely defined using the density function and the vibration amplitude. In an experimental case study Iwan distribution density function in a frictional contact is obtained using measured dissipations at different vibration levels.     

Acrylic coatings exhibiting improved hardness, solvent resistance and glossiness by using silica nano-composites

To prepare nano-composite emulsion acrylic resins with improved surface hardness and solvent resistance, nano-silica particles were treated with surfactants. The monomers of methyl methacrylate/butylacrylate were co-polymerized on the surface of dispersed silica particles. Several emulsions with different silica contents and copolymer mole fractions were prepared. Finally the emulsions were modified to water-based acrylic coatings and improved properties such as surface hardness, solvent resistance and glossiness were determined. The study of coatings was directed to find the improved resin by optimum surface properties. Size distribution and morphology of latexes were characterized by Fourier transform infrared spectroscopy, dynamic light scattering, transmission electron microscopy and scanning electron microscopy. The glass transition temperature of nano-composites was measured and discussed its relation with silica contents, monomer mole fractions and improved properties of coatings. The optimum pendulum hardness of coatings was on 0.46 methyl methacrylate mole fraction and 120 g silica content. An increase in pendulum hardness of nano-composites with the addition of modified silica was observed. DLS and TEM studies indicate that silica particles were dispersed homogenously through the polymer matrix.     

An unexpected tetracyclic product isolated during the synthesis of biscoumarins catalyzed by [MIM(CH2)4SO3H][HSO4]: Characterization and X-ray crystal structure of 7-(2-hydroxy-4-oxo-4H-chromen-3-yl)-6H,7H-chromeno[4,3-b]chromen-6-one

Under solvent-free conditions and in the presence of 3-methyl-1-(4-sulfonic acid)butylimidazolium hydrogen sulfate [MIM(CH₂)₄SO₃H][HSO₄], a Brønsted acidic ionic liquid, the reaction of aromatic aldehydes with 4-hydroxycoumarin has been investigated. A wide range of aromatic aldehydes easily undergoes condensation with 4-hydroxycoumarin to afford biscoumarins with good purity in excellent yields. However, reaction of 2-hydroxybenzaldehyde with 4-hydroxycoumarin gave, not the corresponding biscoumarin, but a tetracyclic compound, 7-(2-hydroxy-4-oxo-4H-chromen-3-yl)-6H,7H-chromeno[4,3-b]chromen-6-one, in high yield.     

Investigation of coupling length in a semi-cylindrical surface plasmonic coupler

We have investigated the performance of a nano-optical directional coupler based on gap plasmon waveguides. The coupler consists of two waveguides having a localized coupled plasmon propagating between two semi-cylindrical surfaces. After introducing a fundamental mode of studied waveguides, effects of the structure parameters on the coupling length are shown. Simulation results of the coupler obtained by the compact-2D finite-difference time-domain (FDTD) method comply with those derived by an analytic method with the aid of the finite-element frequency-domain (FEFD) software package of COMSOL.     

An analysis of the isomerization energies of 1,2-/1,3-diazacyclobutadiene, pyrazole/imidazole, and pyridazine/pyrimidine with the turn-upside-down approach

The isomerization energies of 1,2- and 1,3-diazacyclobutadiene, pyrazole and imidazole, and pyridazine and pyrimidine are 10.6, 9.4, and 20.9 kcal/mol, respectively, at the BP86/TZ2P level of theory. These energies are analyzed using a Morokuma-like energy decomposition analysis in conjunction with what we have called turn-upside-down approach. Our results indicate that, in the three cases, the higher stability of the 1,3-isomers is not due to lower Pauli repulsions but because of the more favorable σ-orbital interactions involved in the formation of two C-N bonds in comparison with the generation of C-C and N-N bonds in the 1,2-isomers.     

Preparation and biological evaluation of radiolabeled-folate embedded superparamagnetic nanoparticles in wild-type rats

In this study, superparamagnetic iron oxide nanoparticles (SPION) embedded by folic acid (SPION-folate) were prepared by a modified co-precipitation method. The structure, size, morphology, magnetic property and relaxivity of the SPION-folate were characterized systematically by means of XRD, VSM, HRSEM and TEM and the interaction between folate and iron oxide (Fe₃O₄) was characterized by FT-IR. The particle size was shown to be ≈5–10 nm. To ensure biocompatibility, the interaction of these SPION with mouse connective tissue cells (adhesive) was investigated using an MTT assay. Consequently, gallium-67 labeled nanoparticles ([⁶⁷Ga]-SPION-folate) were prepared using ⁶⁷Ga with a high labeling efficiency (over 96%, RTLC method) and they also showed an excellent stability at room temperature for at least 2 days and were evaluated for their biodistribution in normal rats up to 24 h compared with free Ga³⁺ cation and [⁶⁷Ga]-SPION biodistribution. The biodistribution of the tracer among 3 other folate tracers were compared, showing lower liver uptake and higher blood circulation after 24 h leading to better bioavailability. The bone:muscle, kidney:muscle, lung:muscle, stomach:muscle ratios were 9.3, 9.32, 7.6 and 5.83 respectively. The developed folate-containing nano-system can be an interesting folate receptor tracer, capable of better cell membrane permeability while possessing paramagnetic properties for thermotherapy.     

Elemental analysis of dust trapped in air conditioner filters for the assessment of Lahore city’s air quality

A study was undertaken to assess the air quality of Lahore by the elemental analysis of air conditioner (AC) filter dust samples collected from 15 different commercial sites. Samples were prepared using the Leeds Public Analyst Method and were analyzed using instrumental neutron activation analysis (INAA) for up to 31 elements. The elements Al, As, Ba, Ce, Co, Cr, Cs, Fe, Hf, K, La, Lu, Mn, Na, Nd, Rb, Sc, Sm, Sn, Ta, Th, Yb and Zn were detected in all 15 samples whereas the remaining elements have been detected in fewer samples; i.e. Mg, Sb and Tb were detected in 14 samples, Br and V in ten samples, U in nine samples and Ca and Ti in eight samples only. Al, Ca, Fe, K, Mg and Na were determined in all samples at percentage levels. The concentrations of most elements were found to lie around the mean values for the 15 samples studied and were not orders of magnitude different. However the concentrations of Ca, Mg, Sn and Zn were found to be more variable and were found to be dependant on activities such as construction, fruit and vegetable handling, tin plating and transport, respectively.     

Synthesis of nanocrystalline γ-Al_2O_3 by sol-gel and precipitation methods for methanol dehydration to dimethyl ether

The capability of sol-gel and conventional precipitation techniques for the synthesis of nanocrystalline γ-alumina was investigated. These catalysts were used for vapor-phase dehydration of methanol to dimethyl ether in a fixed-bed reactor under the same operating conditions (T = 300 ?C, P = 1 bar, LHSV = 2.8, 11.7, 26.1 h?1) and characterized by means of N2 adsorption-desorption, NH3-TPD, XRD, TGA and SEM techniques. According to the experimental results, the catalysts prepared using sol-gel method in non-aqueous medium showed better performance compared with those prepared by other methods.