Chemical processing on microchips for analysis, synthesis, and bioassay

This review describes our recent research on miniaturization of chemical systems. We have developed a miniaturization methodology based on pressure-driven multiphase laminar flow and a highly sensitive detection tool, the thermal lens microscope. Some representative applications of the methodology in the fields of analysis, synthesis, and bioassay are described.     

An asymptotic theorem for a class of nonlinear neutral differential equations

The neutral differential equation is considered under the following conditions: n 2, > 0, = ±1, F(t, u) is nonnegative on [t ₀, ) × (0, ) and is nondecreasing in u (0, infin;), and lim g(t) = as t . It is shown that equation (1.1) has a solution x(t) such that 0}}{\text{.}} \hfill \\ \end{gathered} $$ " align="middle" border="0"> Here, k is an integer with 0 k n–1. To prove the existence of a solution x(t) satisfying (1.2), the Schauder-Tychonoff fixed point theorem is used.     

Improvement of thermoelectric properties of alkaline-earth hexaborides

Thermoelectric (TE) and transport properties of alkaline-earth hexaborides were examined to investigate the possibility of improvement in their TE performance. As carrier concentration increased, electrical conductivity increased and the absolute value of the Seebeck coefficient decreased monotonically, while carrier mobility was almost unchanged. These results suggest that the electrical properties of the hexaboride depend largely on carrier concentration. Thermal conductivity of the hexaboride was higher than 10 W/m K even at 1073 K, which is relatively high among TE materials. Alloys of CaB₆ and SrB₆ were prepared in order to reduce lattice thermal conductivity. Whereas the Seebeck coefficient and electrical conductivity of the alloys were intermediate between those of CaB₆ and SrB₆ single phases, the thermal conductivities of the alloys were lower than those of both single phases. The highest TE performance was obtained in the vicinity of Ca_0.5Sr_0.5B₆, indicating that alloying is effective in improving the performance.     

Nanometer‐sized polyradical particles: Organic magnetic dot array formed on a silicon microfabricated substrate

A magnetically active, purely organic dot array was formed by the selective deposition of polyradical nanoparticles on array‐like‐formed pits on a silicon substrate. The nanometer‐sized polyradical particles, poly(4‐methacryoyloxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl), were prepared by the emulsion polymerization of 4‐methacryloyloxy‐2,2,6,6‐tetramethylpiperidine‐1‐acetoxyl followed by a deprotection reaction and oxidation in air. The size (diameter) and radical spin concentration of the polyradical nanoparticles were tunable between the polymerization and oxidation conditions. Electrochemical studies revealed the redox property of the polyradical nanoparticles. The magnetic response image of the polyradical nanoparticles was obtained by magnetic force microscopy, reflecting their radical spin concentrations. These results suggested a possible approach for the use of organic polyradical nanoparticles as organic magnetic dot arrays. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 521–530, 2007     

Profilometry with compact single-shot low-coherence time-domain interferometry

We describe the performance of a compact single-shot low-coherence interferometric scheme that can be capable of measuring three-dimensional surface profiles and shape. This technique utilizes a polarizing Michelson interferometer and a four-channel polarization phase-stepper optics, which is based on a paired wedge prism, a combined wave plate and a Wollaston prism. The coherence gated surface image can be calculated by the simultaneous acquisition of two interferograms and a DC image on a single CCD camera. The image calculation is based on a novel algorithm to calibrate the imbalanced intensity as well as the deviated arbitrary relative phase of each of the imaging channels. The system can display the transverse cross-sectional images in real-time. To demonstrate the feasibility of this system, a Japanese coin is presented as a 3-D shape measurement example with an image size of 4 mm (horizontal) × 4 mm (vertical) × 160 μm (depth).     

Glass transition and its characteristic length for thin crosslinked polystyrene shells of rodlike capsules

Rodlike capsules consisting of a calcium carbonate core and a crosslinked polystyrene shell were synthesized, and the glass transition temperature (T_g) and characteristic length of the glass transition ξ(T_g) for the thin outer shells were investigated by temperature‐modulated differential scanning calorimetry. The shell thickness ranged from 20 to 129 nm. The ratio of the T_g for the outer shell to the bulk T_g increases with decreasing shell thickness d. The d‐dependence of T_g is interpreted in terms of a simple two‐layer model which assumes that an immobile layer exists near the core‐shell interface. Shells of hollow capsules unexpectedly exhibit a similar d‐dependence of T_g to that for the filled capsules. This is characteristic of the crosslinked polymeric shells, and is attributed to certain spatial heterogeneity of crosslink distribution, and/or to the unstable configuration in the ultrathin shell that does not undergo relaxation due to the crosslink. The latter idea is based on the assumption that unstable configurational state is responsible for the T_g shift from the bulk value observed for nanosized polymeric materials. The ratio of the characteristic length for the shell of the filled capsule to that of the bulk ξ_f(T_g)/ξ_b(T_g) decreases with decreasing d. The results are interpreted in terms of the configurational entropy, and it is also suggested that the configurational state of network polymer chains in the shell affects the characteristic length. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2116–2125, 2008     

New Catalytic Functions of Pd and Pt Catalysts for Hydrogenolysis of Methyl Formate

The catalytic performance of supported Pd and Pt catalysts for the title reaction was greatly improved upon the formation of Pd and Pt alloys. Over Pd and Pt alloys, methyl formate was selectively hydrogenolyzed to methanol, while over metallic Pd and Pt, it was decarbonylated to methanol and carbon monoxide. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nonperturbative deformation of D-brane states by the world sheet noncommutativity

By introducing the noncommutativity in the world sheet, we discuss a modification of the D-brane states in the closed string theory. In particular we show how the world sheet noncommutativity induces a nonperturbative effect to the D-brane states.     

High-contrast, high-intensity laser pulse generation using a nonlinear preamplifier in a Ti:sapphire laser system

We report a high-contrast, high-intensity Ti:sapphire chirped-pulse amplification system that incorporates a nonlinear preamplifier based on optical parametric chirped-pulse amplification (OPCPA). By cooling the Ti:sapphire crystal in the final amplifier down to 77 K, the chirped-pulses are amplified to 2.9 J at a 10 Hz repetition rate without a thermal lensing effect. Pulse compression down to 19 fs duration obtained after amplification indicates a peak power of 80 TW. With the OPCPA, the temporal contrast is significantly improved to better than 7x10(-9) in a few picoseconds interval prior to the main laser pulse.