No abstract

We have improved the efficiency of photoconductive antennas (PCAs) using low-temperature-grown GaAs (LT-GaAs). We found that the physical properties of LT-GaAs photoconductive layers greatly affect the generation and detection characteristics of terahertz (THz) waves. In THz generation, high photoexcited carrier mobility and the presence of a few As clusters in the LT-GaAs are two important factors. In detection, short carrier lifetime and the absence of a polycrystalline structure in the LT-GaAs are significant factors. By optimizing these physical properties, we improved the total dynamic range of THz generation and detection by 15 dB over that obtained by conventional commercially available PCAs. In addition, we replaced the semi-insulating GaAs (SI-GaAs) substrate with a Si substrate, which has a low absorption in the THz region. We proposed a new idea of including a highly insulating Al0.5Ga0.5As buffer layer on the Si substrate. Finally, we confirmed the feasibility of manufacturing PCAs using Si substrates.

We have been investigating a multilayer optical disk applicable to Blu-ray Disc (BD) standard using a photopolymer (2P) sheet in order to realize a recording capacity of 100 GB on a 12-cm-diameter disk. We had already developed a 2P sheet utilizing the multilayer disk. In this study, we developed a BD-type quad-layer disk using the 2P sheet, and investigated readout signals from each layer. The jitter values of layer 0 (L0), layer 1 (L1), layer 2 (L2) and layer 3 (L3) in the quad-layer disk were 6.5%, 7.1%, 7.3% and 6.6%, respectively. According to the analysis of the components of jitter values, the main factor behind the deterioration of jitter values is the crosstalk from adjacent layers. However, the jitter value of each layer was sufficient to reproduce the recorded data. From these results, we proved the feasibility of realizing the BD-type multilayer read-only-memory (ROM) disk with the recording capacity of 100 GB.

The effects of natural and non-natural fatty acids on enhancing the absorption of a hydrophilic marker through a human epithelial cell (Caco-2) monolayer were measured to elucidate the properties of the fatty acids. Fatty acids from C9 to C14 enhanced the absorption depending on the concentration and the carbon chain length. Those fatty acids with longer chains gave a higher permeability coefficient at low concentrations and a lower toxicity than those with shorter chains. The surface energy lowering coefficient (SELC), an intrinsic physico-chemical property, and the critical micellar concentration (CMC) were good criteria for identifying the threshold concentrations of a fatty acid to significantly enhance absorption.

The authors present a new numerical scheme that extends the hyperspherical close-coupling (HSCC) method to the two-electron continuum region. It is based on a matching procedure that joins the hyperspherical wavefunctions onto the asymptotic ones defined in the independent particle coordinates. They examine the scheme using a model e+H problem due to Poet that includes only states with zero angular momentum. The electron-impact cross section for the model e+H(1s) to e+H(Ns) excitation is obtained to at worst 3 significant digits for the final states with (N=2, . . ., 5) and is found stable even above the ionization threshold. A pilot calculation of ionization collision strengths is also presented for this model problem.