A simple technique was developed to fabricate a large-area TiO2 electrode layer using electrospun nanorods for dye-sensitized solar cells (DSSCs). Using this technique, we assembled DSSCs of area ∼1 cm2 consisting of a thin TiO2 nanoparticle layer and a thick TiO2 nanorod layer as electrode. The TiO2 nanorods were obtained by mechanically grinding electrospun TiO2 nanofibers. A titania sol was first spin-coated on a conductive glass plate and a TiO2 nanorod layer was next spray dried on it to fabricate TiO2 nanoparticle/nanorod layers. These layers were subsequently sintered. The best-performing DSSC evaluated under AM1.5G (1 sun) condition gave current density ∼13.6 mA cm−2, open circuit voltage ∼0.8 V, fill factor ∼51% and energy conversion efficiency ∼5.8%.

Using high-resolution direct numerical simulation and arguments based on the kinetic energy flux Π(u), we demonstrate that, for stably stratified flows, the kinetic energy spectrum E(u)(k)∼k(-11/5), the potential energy spectrum E(θ)(k)∼k(-7/5), and Π(u)(k)∼k(-4/5) are consistent with the Bolgiano-Obukhov scaling. This scaling arises due to the conversion of kinetic energy to the potential energy by buoyancy. For weaker buoyancy, this conversion is weak, hence E(u)(k) follows Kolmogorov's spectrum with a constant energy flux. For Rayleigh-Bénard convection, we show that the energy supply rate by buoyancy is positive, which leads to an increasing Π(u)(k) with k, thus ruling out Bolgiano-Obukhov scaling for the convective turbulence. Our numerical results show that convective turbulence for unit Prandt number exhibits a constant Π(u)(k) and E(u)(k)∼k(-5/3) for a narrow band of wave numbers.

The anatase TiO 2 nanofibers of average diameters 60, 100, and 150 nm were fabricated by controlled electrospinning of a polymeric solution and subsequent sintering of the as-spun fibers. The sintered fibers were polycrystalline and composed of densely packed TiO 2 grains of size ∼12 nm. The rutile phase nucleated at the particle interface of the dense anatase TiO 2 nanofibers at a temperature of <570 °C because of the increased surface stress observed in these nanofibers. X-ray and electron diffraction measurements and analysis of the sintered fibers showed that the lattice strain increased with a decrease in the fiber diameter. The diameter-dependent lattice strain is attributed to the increased surface energy in fibers of lower diameter. The strain most likely originates from interplay of the surface charge and grain boundary effects. The absorption spectra of the fibers showed a red shift with an increase in the fiber diameter, which is attributed to an increase in the surface stress with a decrease in the fiber diameter.

In this paper, we describe the recent developments in the field of buoyancy-driven turbulence with a focus on energy spectrum and flux. Scaling and numerical arguments show that the stably-stratified turbulence with moderate stratification has kinetic energy spectrum~-E k k u 11 5OPEN ACCESS RECEIVED on energy spectrum and flux in section 3, and scaling of large-scale quantities in section 4. Section 5 contains a brief description of the dynamics of flow reversal. We conclude in section 6.

In this paper we present scaling results of a FFT library, FFTK, and a pseudospectral code, Tarang, on grid resolutions up to 8192 3 grid using 65536 cores of Blue Gene/P and 196608 cores of Cray XC40 supercomputers. We observe that communication dominates computation, more so on the Cray XC40. The computation time scales as T comp ∼ p −1 , and the communication time as T comm ∼ n −γ2 with γ 2 ranging from 0.7 to 0.9 for Blue Gene/P, and from 0.43 to 0.73 for Cray XC40. FFTK, and the fluid and convection solvers of Tarang exhibit weak as well as strong scaling nearly up to 196608 cores of Cray XC40. We perform a comparative study of the performance on the Blue Gene/P and Cray XC40 clusters.