Fracture of soft cellular solids(Poster session 2, New Frontiers in Colloidal Physics : A Bridge between Micro- and Macroscopic Concepts in Soft Matter)

この論文は国立情報学研究所の電子図書館事業により電子化されました。弾性率が1MPa程度のとてもやわらかいセル固体(多孔質物質)の破壊エネルギーを有限サイズ効果なしに直接測定した。非架橋ポリエチレン(PE)フォームに対する系統的な実験から、ヤング率、破壊エネルギー、応力拡大係数と固体分率(あるいは発泡倍率)の間のスケーリング法則を得た。この法則は従来知られていた弾性率が3000MPa以上の場合と異なっているが、シンプルに説明することができる。また、ポリウレタン(PU)フォームについて行った同様の実験の結果についても触れる。We measured directly the fracture surface energy of soft cellular solids (porous materials) of the Young modulus E around 1MPa, with removing finite size effects. From a systematic tests on non-crosslinked polyethylene (PE) foam (Fig. 1), we obtained dependences of Young modulus, fracture energy, and stress intensity factor on solid fraction. These relations differ from what have been known for hard cellular solids of E larger than 3000MPa but can be interpreted by simple notions. We also mention similar tests performed on crosslinked polyurethane foam (Fig. 2)

Characterization of thylakoid membrane in a heterocystous cyanobacterium and green alga with dual-detector fluorescence lifetime imaging microscopy with a systematic change of incident laser power

Fluorescence Lifetime Imaging Microscopy (FLIM) has been applied to plants, algae and cyanobacteria, in which excitation laser conditions affect the chlorophyll fluorescence lifetime due to several mechanisms. However, the dependence of FLIM data on input laser power has not been quantitatively explained by absolute excitation probabilities under actual imaging conditions. In an effort to distinguish between photosystem I and photosystem II (PSI and PSII) in microscopic images, we have obtained dependence of FLIM data on input laser power from a filamentous cyanobacterium Anabaena variabilis and single cellular green alga Parachlorella kessleri. Nitrogen-fixing cells in A. variabilis, heterocysts, are mostly visualized as cells in which short-lived fluorescence (≤ 0.1 ns) characteristic of PSI is predominant. The other cells in A. variabilis (vegetative cells) and P. kessleri cells show a transition in the status of PSII from an open state with the maximal charge separation rate at a weak excitation limit to a closed state in which charge separation is temporarily prohibited by previous excitation(s) at a relatively high laser power. This transition is successfully reproduced by a computer simulation with a high fidelity to the actual imaging conditions. More details in the fluorescence from heterocysts were examined to assess possible functions of PSII in the anaerobic environment inside the heterocysts for the nitrogen-fixing enzyme, nitrogenase. Photochemically active PSII:PSI ratio in heterocysts is tentatively estimated to be typically below our detection limit or at most about 5% in limited heterocysts in comparison with that in vegetative cells