Integrated TiO2 resonators for visible photonics

We demonstrate waveguide-coupled titanium dioxide (TiO(2) racetrack resonators with loaded quality factors of 2.2×10(4) for the visible wavelengths. The structures were fabricated in sputtered TiO(2) thin films on oxidized silicon substrates using standard top-down nanofabrication techniques, and passively probed in transmission measurements using a tunable red laser.     

Unidirectional and wavelength-selective photonic sphere-array nanoantennas

We design a photonic sphere-array nanoantenna (NA) exhibiting both strong directionality and wavelength selectivity. Although the geometric configuration of the photonic NA resembles a plasmonic Yagi-Uda NA, it has different working principles and, most importantly, reduces the inherent metallic loss from plasmonic elements. For any selected optical wavelength, a sharp Fano resonance by the reflector is tunable to overlap spectrally with a wider dipole resonance by the sphere-chain director, leading to high directionality. This Letter provides design principles for directional and selective photonic NAs, which are particularly useful for photon detection and spontaneous emission manipulation.     

Angular response of thin-film organic solar cells with periodic metal back nanostrips

We theoretically study the angular response of thin-film organic solar cells with periodic Au back nanostrips. In particular, the equation of the generalized Lambert's cosine law for arbitrary periodic nanostructure is formulated. We show that the periodic strip structure achieves wide-angle absorption enhancement compared with the planar nonstrip structure for both the s- and p-polarized light, which is mainly attributed to the resonant Wood's anomalies and surface plasmon resonances, respectively. The work is important for designing and optimizing high-efficiency photovoltaic cells.     

Lax representation and Kronecker product

We show how the Kronecker product can be used to find new Lax representations.     

Characterization of 90° domain structure and polarization switching in Pb(Zr0.4Ti0.6)O3 film by piezoresponse force microscope

A lead zirconate titanate Pb(Zr_0.4Ti_0.6)O₃ (PZT40/60) film was deposited on a Pt(111)/Ti/SiO₂/Si(100) substrate by a sol–gel process followed by thermal annealing at 650 °C for 5 min. Piezoresponse force microscope observation revealed a lamellar domain structure in the PZT40/60 grains and we attribute the lamellar domains as 90° ferroelectric domains. The polarization-switching mechanism of the 90° domains in the PZT40/60 film under external electric fields has also been studied and it was revealed that a large-area polarization switching is usually accompanied by the appearance of a new direction of 90° domains in order to reduce the stress in the grains. By contrast, a nanometer-sized polarization switching is believed to be accomplished by generating 180° domains within a single lamellar domain. PACS 77.80.-e; 77.84.-s; 68.55.-a; 68.37.-d     

Efficient MCMC estimation of some elliptical copula regression models through scale mixtures of normals

This paper proposes an efficient estimation method for some elliptical copula regression models by expressing both copula density and marginal density functions as scale mixtures of normals (SMN). Implementing these models using the SMN is novel and allows efficient estimation via Bayesian methods. An innovative algorithm for the case of complex semicontinuous margins is also presented. We utilize the facts that copulas are invariant to the location and scale of the margins; all elliptical distributions have the same correlation structure; and some densities can be represented by the SMN. Two simulation studies, one on continuous margins and the other on semicontinuous margins, highlight the favorable performance of the proposed methods. Two empirical studies, one on the US excess returns and one on the Thai wage earnings, further illustrate the applicability of the proposals.     

ZnO nanorods grown on ZnSe particles by the chemical vapor deposition method

A novel structure of ZnO nanorods on microsized ZnSe particles has been prepared through a chemical vapor deposition technique using Zn and Se powders as the sources. The dimension of the nanorods can be controlled by adjusting the growth temperature, time and the Zn : Se ratio. Through the investigation of the effects of synthesis time and Zn : Se ratio on the formation of ZnO nanorods on ZnSe microparticles, it is proposed that the synthesis of the ZnO–ZnSe structures involves a two-stage formation. The growth of ZnO nanorods can be described by the vapor–solid mechanism. The photoluminescence of the ZnO–ZnSe structures has also been studied. PACS 73.21.-b; 78.55.Et; 61.10.Nz; 61.46.+w; 68.65.-k     

Predicting thermal conductivity of liquid suspensions of nanoparticles (nanofluids) based on rheology

A methodology is proposed for predicting the effective thermal conductivity of dilute suspensions of nanoparticles (nanofluids) based on rheology.The methodology uses the rheological data to infer microstructures of nanoparticles quantitatively,which is then incorporated into the conventional Hamilton-Crosser equation to predict the effective thermal conductivity of nanofluids.The methodology is experimentally validated using four types of nanofluids made of titania nanoparticles and titanate nanotubes dispersed in water and ethylene glycol.And the modified Hamilton-Crosser equation successfully predicted the effective thermal conductivity of the nanofluids.     

Thermal conductivity of gel-spun polyethylene fibers

The thermal conductivities of unidirectional gel-spun polyethylene fiber-reinforced composites have been measured parallel (K∥?) and perpendicular (K⊥) to the fiber axis from 15 to 300K. The axial thermal conductivity K∥? varies linearly with volume fraction v_f of fiber, while the transverse thermal conductivity K⊥ follows the Halpin-Tsai equation. Extrapolation to v_f = 1 gives the thermal conductivity of gel-spun polyethylene fiber which, at 300K, has values of 380 and 3.3 mW cm^?1K^?1 along and perpendicular to the fiber axis, respectively. The axial thermal conductivity is exceptionally high for polymers, and is more than twice the thermal conductivity of stainless steel. This high value arises from the presence of a large fraction of long (> 50 nm) extended chain crystals in the fiber. Further improvement of up to a factor of 10 is possible if the length and volume fraction of the extended chain crystals can be increased. © 1993 John Wiley & Sons, Inc.