SUMMARYAn efficient dual boundary element technique for the analysis of a two-dimensional finite body with multiple cracks is established. In addition to the displacement integral equation derived for the outer boundary, since the relative displacement of the crack surfaces is adopted in the formulation, only the traction integral equation is established on one of the crack surfaces. For each crack, a virtual boundary is devised and connected to one of the crack surfaces to construct a closed integral path. The rigid body translation for the domain enclosed by the closed integral path is then employed for evaluating the hypersingular integral. To solve the dual displacement/traction integral equations simultaneously, the constant and quadratic isoparametric elements are taken to discretize the closed integral paths/crack surfaces and the outer boundary, respectively. The present method has distinct computational advantages in solving a fracture problem which has arbitrary numbers, distributions, orientations and shapes of cracks by a few boundary elements. Several examples are analysed and the computed results are in excellent agreement with other analytical or numerical solutions.

This paper presents an integration of molecular simulation with computational mass transfer to predict the photocurrent-voltage ͑I-V͒ performance of photoelectrochemical solar cells. It aims at developing a general simulator for ionic-liquid-type photoelectrochemical cells, excluding the prediction of the incident photon-to-current efficiency and the injection efficiency parts. The charge transport in the electrolyte, typically iodide/tri-iodide ionic liquid, is mainly in the molecular diffusion mechanism, which partly limits the solar cell performance. The molecular dynamics technique is employed to assess the ionic conductivity and diffusion coefficient of the charge transfer. The ionic conductivity is compared with a published experimental result carried out by an impedance test. The corresponding diffusion coefficient is then inputted to a computational mass transfer code, and the depletion of redox charges at the electrode can be calculated. The electrochemical performance of the solar cell is predicted and shown in reasonable agreement with experimental I-V results.Photoelectrochemical cells, especially dye-sensitized solar cells ͑DSSCs͒, are potentially the future of photovoltaic cells because of their prevailingly lower cost than all the other types of solar cells. 1 Although the current efficiency is only acceptable ͑2-11%͒, 2-5 DSSCs are thin, light, flexible, and mainly abundant from a raw material aspect. The basic configuration of a DSSC consists of an electrode ͑anode͒ and an opposite counter electrode ͑cathode͒ with an electrolyte between them, as shown in Fig. 1. The electrode is a glass substrate made of transparent conducting oxide, which is coated by a 10-20 m film of nanocrystalline TiO 2 particles ͑10-30 nm diameters͒ that is covered by a monolayer of dye molecules. Pores of the nanocrystalline TiO 2 film are filled with an ionic liquid containing a redox couple ͑e.g., I − /I 3 − ͒ in a nonaqueous solution, such as liquid ammoniates. The counter electrode is placed in the opposite side, and the whole cell has to be well sealed. Under the photoexcitation condition, the dyes absorb photons and inject electrons into the TiO 2 conduction band. The electrons travel through the nanocrystalline TiO 2 film and are collected at the anode. After passing through the external circuit and delivering power to the external load, the electrons re-enter the cell at the cathode. The tri-iodide ions nearby are reduced to iodide ions, which then diffuse to the porous TiO 2 film via the electrolyte, to reduce the photooxidized dyes back to the original state. The best reported efficiency of this kind of solar cells in research laboratories is about 10.6%, stated by Grätzel. 6 This still needs more verification and further improvement for commercialization. This paper starts by studying the fundamental nanoscopic transport phenomena in the ionic liquid electrolyte between the anode and the cathode. This is because the slowest mechanism and the major potential loss of this kind of photoelectrochemical solar cells m...

By means of microfluidic analysis with a thermal lattice-Boltzmann method, we investigated the hydrophilic, thermal and geometric effects on the dynamics of CO 2 bubbles at anode microchannels (e.g., porous layers and flow channels) of a micro-direct methanol fuel cell. The simulation results show that a more hydrophilic wall provides an additional attractive force to the aqueous methanol in the flow direction and that moves the CO 2 bubble more easily. The bubble propagates quicker in the microchannel with a positive temperature gradient imposed from the inlet to the exit, mainly due to the Marangoni effect. Regarding the geometric effect of the microchannel, the bubble moves more rapidly in a divergent microchannel than in a straight or convergent channel. On the basis of the quantitative evaluation of hydrophilic, thermal and geometric effects, we are able to design the bubble-removal technique in micro fuel cells.Keywords Thermal lattice-Boltzmann method Á Bubble dynamics Á Two-phase flow Á Micro-direct methanol fuel cell List of symbols e lattice velocity vector e lattice speed (cm/s) f density distribution function (g/cm 3 ) g thermal distribution function (g K/cm 3 ) G rr 0 interaction strength between the species r and the other species r 0 (cm 3 /g s)

No abstract

First principles density functional theory calculations within the generalized gradient approximation are performed to comprehensively study the structural, elastic, electronic and thermodynamic properties of triclinic single and polycrystalline Cu7In3. The polycrystalline elastic properties are predicted using the Voigt-Reuss-Hill approximation and the thermodynamic properties are evaluated based on the quasi-harmonic Debye model. Their temperature, hydrostatic pressure or crystal orientation dependences are also addressed, and the predicted physical properties are compared with the literature experimental and theoretical data and also with those of three other Cu-In compounds, i.e., CuIn, Cu2In and Cu11In9.The present calculations show that in addition to being a much better conductor compared to Cu2In and Cu11In9, Cu7In3 crystal reveals weak elastic anisotropy, high ductility and low stiffness, and tends to become more elastically isotropic at very high hydrostatic pressure. Moreover, the Cu7In3 holds the largest high-temperature heat capacity among the four Cu-In compounds.