Geometrical Form Factor Improvement for Receiving System of Infrared Lidar

Improvement of an infrared light detection and ranging (IR-lidar) system for a short range (0–1000 m) and with high resolution is studied to enhance a geometrical form factor. Theoretical modeling of Mie scattering echo signals agrees with the experimental results. Introduction of a lens in front of the detector is effective for increasing the geometrical form factor, and a significant improvement in the received signal intensity is achieved, especially for short-range measurements around 100 m. This is useful for the IR-lidar system with a detector diameter of less than 1 mm. In the theoretical model, a ray-tracing technique was applied and a transmitting laser beam with Gaussian profile was considered for better accuracy.     

Polarization-Dependent Phase-Conjugate Reflectivity in Randomly Oriented Saturable Absorbers: Effects of Direction of Transition Dipole Moment Associated with Excited-State Absorption

The effects of the direction of transition dipole moment on polarization-dependent phase-conjugate (PC) reflectivity by degenerate four-wave mixing in a saturable-dye-doped film are theoretically investigated. On the basis of a four-energy-level model for the saturable dyes, the pump-intensity dependence of the PC reflectivity is calculated for the two cases of a probe wave being polarized either parallel or perpendicular to pump waves, when the transition dipole moment associated with excited-state absorption tilts from that associated with ground-state one. For the parallel polarization, in the case of two transition dipole moments having different directions, a dip appears in the PC reflectivity curve near a resonant frequency on account of the characteristics of nonlinear absorption, whereas it disappears when the frequency of light is off resonance due to the influence of nonlinear refractive index.     

High Efficiency Electrically-Addressable Phase-Only Spatial Light Modulator

To realize a high efficiency electrically addressable phase-only modulator, we have coupled a liquid crystal display (LCD) to an optically addressed parallel-aligned nematic liquid crystal spatial light modulator (PAL-SLM) with a set of lenses. Phase modulation exceeding 3ϖ at 532 nm wavelength was obtained. We obtained linear transfer characteristics for phase modulation at various desired phase levels after calibration and adjustment of the transfer characteristics of the PAL-SLM and the LCD. Diffraction efficiency of 40% for binary phase grating and of 90% for 8-level blazed phase grating, which were very close to the simulation values, were observed. The power loss of the readout light was caused when passed through a half mirror, therefore, we examined a setup using an oblique readout light at the modulator. Very high diffraction efficiency was obtained from the setup by optimizing the polarization direction and optical path for this light, and the orientation of liquid crystals. Since the modulator can perform at better than 90% diffraction efficiency and at nearly 100% reflectivity, various high efficiency systems utilizing such modulators are expected.     

Ultrasonic effects on electroorganic processes: Part 16. Stereoselectivity control of hydrodimers formed in cathodic reduction of acetophenones

Stereoselectivity (meso/dl ratio) of the hydrodimers (HDs) formed in cathodic reduction of acetophenones was greatly affected by ultrasonic irradiation with power higher than an ultrasonic cavitation threshold in weakly acidic solutions, while such an ultrasonic effect on stereocontrol was not observed in either strongly acidic or alkaline solutions.     

Asymmetric anionic polymerization of maleimides bearing bulky substituents

Asymmetric anionic homopolymerizations of N‐substituted maleimide (RMI) bearing bulky substituents [R = benzyl, diphenylmethyl (DPhMI), 9‐fluorenyl (9‐FlMI), triphenylmethyl, (diphenylmethyloxycarbonyl)methyl, (9‐fluorenyloxycarbonyl)methyl] were carried out with complexes of organometal compounds (alkyllithium, diethylzinc) with six chiral ligands to obtain optically active polymers. The chiroptical properties of the polymers were affected strongly by the substituents on nitrogen in the maleimide ring, the organometal and chiral ligands. Poly(DPhMI) initiated by an n‐butyllithium/(−)‐sparteine (Sp) complex showed a positive specific rotation ([α] +60.3°). Poly(9‐FlMI) prepared with a florenyllithium/Sp complex exhibited the highest specific rotation (+65.7°). The specific rotations of the poly(RMI) obtained were attributed to different contents between the stereogenic centers (S,S) and (R,R) based on threo‐diisotactic structures of the main chain. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 310–320, 2000     

Simultaneous construction of a polyether backbone and a variety of keto side chains by three‐component polycondensation: An improved method for the use of a variety of silyl enol ethers

For the synthesis of polyethers with a variety of keto side chains in a one‐step reaction, the three‐component polycondensation of dialdehydes, diol disilyl ethers, and silyl enol ethers of ketones was investigated. The method of monomer addition strongly affected the molecular weight of polymers and was optimized to yield high molecular weight polymers by model reactions. A variety of dialdehydes, diol disilyl ethers, and silyl enol ethers were polymerized in the presence of a catalytic amount of triphenylmethyl (trityl) perchlorate in CH₂Cl₂ at −78 °C according to the method of monomer addition. This polymer synthesis was unusual in that it concurrently constructed both the polyether backbone and the keto side chains from three starting compounds. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 179–188, 2000     

Graft copolymers having hydrophobic backbone and hydrophilic branches. XXX. Preparation of polystyrene‐core nanospheres having a poly(2‐methacryloyloxyethyl phosphorylcholine) corona

Polystyrene core nanosphere particles possessing 2‐methacryloyloxyethyl phosphorylcholine (MPC) polymers on the corona were prepared by the free radical polymerization of hydrophilic polyMPC macromonomer and hydrophobic styrene with AIBN as a radical initiator in ethanol as a polar solvent. The morphology of the nanospheres was observed by transmission electron micrograph (TEM). The nanospheres were spherical in form and have a narrow size distribution. Their sizes could be controlled by varying the molecular weight of the macromonomer and the amount of it in feed. Electron spectroscopy for chemical analysis (ESCA) of the nanosphere surfaces suggested that polyMPC chains were located favorably on the surface of the nanosphere. The nanospheres having the polyMPC chains on their surfaces can be significant and useful materials in technological and medical fields. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3052–3058, 2000     

Biological activity of chitosan–sugar hybrids: specific interaction with lectin

The specific interactions between lectins and chitosan–sugar hybrids, the synthesized chitosan derivatives linking carbohydrate residue to the amino group of chitosan, were investigated. The specific bindings of chitosan‐L ‐fucose (Fuc) hybrid with Ulex europaeus agglutinin I (UEA I, a lectin specific to L ‐Fuc), and chitosan‐N‐acetyl‐D ‐glucosamine (D ‐GlcNAc) hybrid with Concanavalin A (Con A, a lectin specific to D ‐glucose, D ‐mannose and D ‐GlcNAc), were confirmed by a surface plasmon resonance technique. The microscopic observation of Pseudomonas aeruginosa, which was preincubated with the fluorescein isothiocyanate‐labeled chitosan‐L ‐Fuc hybrid, showed bacteria aggregation. The aggregation was thought to be resulted from the specific interaction of the L ‐Fuc residue of the hybrid with PA‐II lectin on the surface of P. aeruginosa. The chitosan‐L ‐Fuc hybrid inhibited P. aeruginosa growth more effectively in comparison with the other hybrids or unmodified chitosan. The enhancement of antimicrobial activity of chitosan‐L ‐Fuc hybrid could be attributed to the specific binding between PA‐II lectin of P. aeruginosa and L ‐Fuc residue of the L ‐Fuc hybrid. Copyright © 2000 John Wiley & Sons, Ltd.     

Novel method for preparation of poly(benzoxazinone‐imide)

A novel method was developed to prepare poly(benzoxazinone‐imide) by the dealcoholization of poly(amide‐imide), having pendent ethoxycarbonyl groups, which was prepared from poly(amide acid). The poly(amide acid) was prepared from the reaction of pyromellitic dianhydride and 4,4′‐diamino‐6‐ethoxycarbonyl benzanilide. The curing behavior of the poly(amide acid) was monitored by DSC, which indicated the presence of two broad endotherms, one with maximum at 153 °C due to imide‐ring formation and the other with maximum at 359 °C due to benzoxazinone‐ring formation. The poly(amide acid) was thermally treated at 300 °C/1 h to get poly(amide‐imide) with pendent ester groups, then at 350 °C/2 h to convert into poly(benzoxazinone‐imide) by dealcoholization. Viscoelastic measurements of the poly(amide‐imide) showed that the storage modulus dropped at about 280 °C with glass‐transition temperature (T_g ) at about 340 °C. The storage modulus of poly(benzoxazinone‐imide), however, was almost constant up to 400 °C and no T_g was detected below 400 °C. Also, the tensile modulus and tensile strength of the poly(benzoxazinone‐imide) was much higher than that of the poly(amide‐imide). The 5% decomposition of poly(benzoxazinone‐imide) film was at 535 °C, which reflects its excellent thermal stability. Also, poly(benzoxazinone‐imide) showed more hydrolytic stability against alkali in comparison to polyimides. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1647–1655, 2000