First-principles study of the electronic,optical and bonding properties in dolomite

The structural, electronic, optical properties and chemical bonding of dolomite CaMg(CO₃)₂ (rhombohedral calcite-type structure) are investigated using plane wave pseudopotential density-functional theory (DFT) method taking the local density approximation (LDA) and the generalized gradient approximation (GGA) as the exchange–correlation energy functional. The structural properties are consistent with the early experimental and theoretical results. The indirect electronic band gap is estimated to be ～5.0 eV, which is less than the optical band gap measured from the fundamental absorption edge of ～6.0 eV. The optical band gap is also consistent with the experimental band gap of similar calcite-type structure. A noticeable difference for the LDA and GGA derived transition peaks and a significant optical anisotropy are observed in the optical spectra. The analysis of electronic density of states, Mulliken charge and bonding population shows the coexistence of covalent and ionic bonding in the dolomite structure and the results are consistent with previous theoretical calculations.     

Diffusive Thermoelectric Power in Highly Asymmetric Bilayer Graphene Nanoribbons

We present a simplified theoretical analysis of diffusive thermoelectric power (TEP) in a highly asymmetric bilayer graphene nanoribbon (BGN) within the framework of the tight binding formalism. BGN possesses two sets of subbands, the upper and the lower. We have shown that, for a highly asymmetric BGN (?? = ??, where ?? and ?? are the gap and interlayer coupling constant, respectively), the density of states in the lower set of subbands increases compared with the upper. The effect of ribbon width on the TEP under the aforementioned phonon scattering regime has also been quantitatively shown. The TEP exhibits an oscillatory dependence on ribbon width. Reflection coefficients of the carriers in both the upper and lower subbands have been treated in detail. Results of the ballistic formalism have been obtained as a special case in the present analyses under certain limiting conditions, forming an indirect validation of our theoretical formulations.     

Robust STATCOM control for the stabilisation of fixed-speed wind turbines during low voltages

This paper presents a robust voltage control scheme for fixed-speed wind generators using a static synchronous compensator (STATCOM) controller. To enable a linear and robust control framework with structured uncertainty, the overall system is represented by a linear part plus a nonlinear part that covers an operating range of interest required to ensure stability during severe low voltages. The proposed methodology is flexible and readily applicable to larger wind farms of different configurations. The performance of the control strategy is demonstrated on a two area test system. Large disturbance simulations demonstrate that the proposed controller enhances voltage stability as well as transient stability of induction generators during low voltage ride through (LVRT) transients and thus enhances the LVRT capability.     

High Resolution Study of Micrometer Particle Detachment on Different Surfaces

In an effort to identify particle initial motion prior liftoff interactions of micrometer glass beads (10–100 μm) on glass, ceramic, and hardwood substrates were investigated experimentally. Particles were deposited on the lower surface of a 10 cm² wind tunnel by gravitational settling. Air flows were imposed from an open entrance at average velocities up to 16 m/s. Individual particle trajectories obtained by high-speed imaging reveal three different types of motion: rolling/bouncing (saltation caused by the movement of hard particles over an uneven surface in a turbulent flow of air), immediate liftoff (particles completely leave the surface with no or minimal initial rolling/bouncing) and complex motion (particles travel with rolling/bouncing motion on the surface for a certain distance before final liftoff). Surface roughness significantly affects the particle initial motion prior to liftoff. The majority of particle trajectories from the glass substrate were parallel to the surface with complex motion. Hardwood substrates took the longest time for initial particle movement (t >1 s) causing a more rapid liftoff. The ceramic substrate showed the most rolling/bouncing motion, for 80% of the particles. The detachment percentage initially follows an exponentially increasing trend for a period of ～1 s, followed by a plateau phase for a period of 5 s. Changing the velocity, substrate, and particle size significantly affects particle detachment. Incorporating the different types of particle motion prior to liftoff into detachment mode models, and understanding how their relative contributions change with different particle and substrate materials, can potentially yield improved predictive capabilities.

Copyright 2013 American Association for Aerosol Research     

Proton conducting hybrid membrane electrolytes of sulfonated poly(ether sulfone)s and poly(ether sulfone)s containing metallophthalocyanine

A role of metallophthalocyanine (MPc) as an anti-oxidizing agent of polymer membrane and an accelerating agent of proton conductivity was discussed. The poly(ether sulfone)s bearing MPc (Ni, Co and Fe), PMPc were prepared by two-step reaction from phenolphthalein and fumaronitrile and followed reaction with metal (II) chloride (Ni, Co and Fe) and 1,2-dicyanobenzene in quinoline. The sulfonated polymer was synthesized by condensation polymerization using 1,2-bis(4-hydroxyphenyl)-1,2-diphenyl ethylene, bis(4-fluorophenyl) sulfone and followed by sulfonation reaction with concentrated sulfuric acid. A series of hybrid membranes (H–Ni, H–Co and H–Fe) were prepared from a mixture of the sulfonated copolymer and PMPcs in dimethylacetamide (DMAc). The structural properties of the synthesized polymers were studied by ¹H-NMR spectroscopy and FT-IR. The membrane properties were investigated by measurements of ion exchange capacity (IEC), water uptake, and proton conductivity, chemical degradation test, and atomic force microscopy (AFM) analysis. The cell performance of the membranes was compared with those of normal sulfonated poly(ether sulfone)s and Nafion.     

Structures and Stabilities of the Metal Doped Gold Nano-Clusters: M@Au10 (M = W,Mo, Ru,Co)

The structures and stabilities of a series of endohedral gold clusters containing ten gold atoms M@Au₁₀ (M = W, Mo, Ru, Co) have been determined using density functional theory. The gradient-corrected functional BP86, the Tao-Perdew-Staroverov-Scuseria TPSS meta-GGA functional, and the hybrid density functionals B3LYP and PBE1PBE were employed to calculate the structures, binding energies, adiabatic ionization potentials, and adiabatic electron affinities for these clusters. The LanL2DZ effective core potentials and the corresponding valence basis sets were employed. The M@Au₁₀ (M = W, Mo, Ru, Co) clusters have higher binding energies than an empty Au₁₀ cluster. In addition, the large HOMO–LUMO gaps suggest that the M@Au₁₀ (M = W, Mo, Ru, Co) clusters are all likely to be stable chemically. The ionization potentials and electron affinities for these clusters are very high, and the W@Au₁₀ and Mo@Au₁₀ clusters have electron affinities similar to the super-halogen Al₁₃.     

Case-Based Reasoning for Real-Time Traffic Flow Management

Real-time traffic management is a promising approach for alleviating congestion. This approach uses real-time and predicted traffic information to develop routing strategies that optimize the performance of highway networks. This article explores the potential for using case-based reasoning (CBR), an emerging artificial intelligence (AI) paradigm, to overcome the limitations of existing traffic-management decision support systems. To illustrate the feasibility of the approach, the article develops and evaluates a prototype CBR routing system for a real-world network in Hampton Roads, Virginia. Cases for building the system's case base are generated using a heuristic dynamic traffic assignment (DTA) model specifically designed for the region. Using a set of 25 new independent cases, the performance of the prototype system is evaluated by comparing its solutions with those of the DTA model. The evaluation results demonstrate the feasibility of the CBR approach. The prototype system was capable of running in real time and produced high-quality solutions using case bases of reasonable size.     

Behavior of Ground and Response of Existing Foundation Due to Tunneling

An apparatus has been developed to model the excavation of a tunnel in the laboratory. With this apparatus, 2D model tests are carried out to investigate the surface settlement and the earth pressure brought about by the tunneling. Finite element analyses using an elastoplastic subloading t_ij model are also conducted. The influence of volume loss on the surface settlement and the earth pressure, due to the shallow tunnelling, is illustrated based on the model tests and the corresponding numerical analyses. It is revealed that the surface settlement troughs and the earth pressure distributions around shallow tunnels depend on both the volume loss and the crown drift of the tunnel. The effect of the interaction between the tunneling and existing nearby foundations is also demonstrated in this paper. For existing foundations, the building loads control the surface settlements and the zone of deformation during the tunnel excavation. The behavior of the foundations depends on the deformation mechanism of the ground during the tunnel excavation. The induced axial force and bending moments in the piles of a piled raft are investigated numerically, and it is shown that the axial force changes due to the stress relaxation of the ground. Bending moments are induced in the piles at a lower value of soil cover due to the differential settlement of the piled raft.     

Novel cyclic sulfonium iodide containing siloxane high performance electrolyte for dye-sensitized solar cell

A new type of solid and gel state electrolytes based on siloxane cyclic sulfonium iodides was synthesized and used in dye-sensitized solar cells. The resulting electrolytes were characterized by ¹H NMR, TGA, diffusion coefficient, and ion conductivity. The thermo-oxidative stabilities of the prepared ionic species are lower than that of DMII because the bond strength of S⁺–C in thiophenium is lower than that of N⁺–C in imidazolium. Among the three SiCSIs based electrolytes, SiCSI3 showed a maximum photo-conversion efficiency of 7.3%. In addition, the performance of the DSSCs showed relatively reasonable compared with the imidazolium type DMII electrolyte.