We report numerical analysis and experimental observation of two-dimensionally localized plasmonic modes guided by a nano-gap in a thin metal film. Dispersion, dissipation and field structure of these modes are analyzed using the finite-difference time-domain algorithm. The experimental observation is conducted by the end-fire excitation of the proposed gap plasmon waveguides and detection of the generated modes using their edge scattering and CCD camera imaging. Physical interpretation of the obtained results is presented and origins of the described modes are discussed.

Coherent control of the precession motion of magnetizations in a single crystal YFeO3 with double half-cycle pulse terahertz waves was demonstrated. Quasiferromagnetic (0.299 THz) and quasiantiferromagnetic (0.527 THz) precession modes were selectively excited by choosing an appropriate interval of two pulses and were observed as free induction decay (FID) signals from the spin system. By observing the circularly polarized FID signals due to ferromagnetic resonance, we also succeeded in confirming directly the energy storage in the spin system and recovery from that to the electromagnetic radiation.

Terahertz time domain spectroscopy was performed on orthoferrite ErFeO3. Through the emission from the two magnetic resonance modes, we succeeded in observing the spin reorientation transition. Depending on the orientation of the single crystal, the reorientation can be detected as either mode switching between the two modes or polarization change of the emission. This method enables picosecond resolved observation of the reorientation without disturbances such as electronic excitation and heating, and it is expected to open the doorway to observe ultrafast reorientation with the terahertz pulse.

Spacer-modified anion exchange resins were prepared by suspension copolymerization of v-bromoalkylstyrenes or v-bromoalkyloxymethylstyrenes with 2-8 mol % of divinylbenzene, followed by quaternization with trimethylamine. The thermal stability of the spacer-modified anion exchangers of the OH form was examined by standing the resins in deionized water at 100-140ЊC for 30-90 days. The anion exchangers with alkylene chains such as butylene or heptylene groups between the benzene ring and the quaternary nitrogen exhibited higher thermal stability compared with commercial, strongly basic anion exchangers with benzylic ammonium groups. The thermal stability of the exchangers with butyleneoxymethylene or hexyleneoxymethylene spacers was also higher than that of the commercial exchangers. The exchanger with the propyleneoxymethylene spacer, however, had less stability than did the commercial ones. The decreased stability of this spacer-modified exchanger is due to the accelerated degradation of the spacer chain via Hofmann elimination. The excellent stability of the anion exchangers with alkylene or alkyleneoxymethylene spacers, except propyleneoxymethylene, results from the structure of the exchangers, where there are no reactive benzylic carbons, which are attached directly to the quaternary nitrogen.

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