Comparison of radioactive and stable cesium uptake in aquatic macrophytes affected by the Fukushima Dai-ichi Nuclear Power Plant accident

Concentrations of ^134+137Cs and ¹³³Cs in aquatic macrophytes, water, and sediment were measured in samples collected from Fukushima Prefecture, Japan. The concentrations of ¹³⁷Cs in submerged and floating-leaved plants were higher than the values for emergent plants according to their main Cs uptake mode. The geometric mean water-to-plant concentration ratio for ¹³⁷Cs and ¹³³Cs was comparable observed in submerged and floating-leaved plants, while the geometric mean sediment-to-plant concentration ratio for ¹³⁷Cs in emergent plants was higher than that of ¹³³Cs, which suggest that the mobility of Fukushima accident-derived ¹³⁷Cs is not in steady state 4–5 years after the accident.

     

Constructing self-organized structures on silicon and sapphire surfaces

We investigated methods to fabricate distinctive structures on silicon and sapphire substrates to grow a carbon nanotube (CNT) network using a solution from the Belousov-Zhabotinsky (BZ) reaction. The BZ reaction is a chemical system where chemical reactions and material diffusion coexist in a nonequilibrium state and generate spatiotemporal patterns in a petri dish. Precipitates from the reaction should also produce distinctive structures after being piled on the substrates. The structures have metal particles that act as catalysts for growing CNTs or quantum dots of nanodot devices. Therefore, such structures should be suitable to fabricate three-dimensional CNT networks or nanodot devices. To confirm this, we investigated the fabrication of distinctive structure using a BZ reaction solution. Results indicated that the BZ reaction solution produced interesting structures on the substrates. Moreover, we confirmed that the shape of the structure changed when the substrate used was changed. We believe that the developed methods are suitable to fabricate nanodevices, especially CNT network devices.     

Asymptotic formalism for ultraflat optical frequency comb generation using a Mach-Zehnder modulator

We theoretically prove that a conventional Mach-Zehnder modulator can generate an optical frequency comb with excellent spectral flatness. The modulator is asymmetrically dual driven by large amplitude sinusoidal signals with different amplitudes. The driving condition to obtain spectral flatness is analytically derived and optimized, yielding a simple formula. This formula also predicts the conversion efficiency and bandwidth of the generated frequency comb.     

Improved optical enrichment of SWNTs through extraction with chiral nanotweezers of 2,6-pyridylene-bridged diporphyrins

Chiral single-walled carbon nanotubes (SWNTs) have left- and right-handed helical structures (M and P, respectively, according to the IUPAC nomenclature). In this report, optically active SWNTs were obtained through preferential extraction of (M)- or (P)-SWNTs with 2,6-pyridylene-bridged chiral diporphyrins 1. In the circular dichroism (CD) spectra, the SWNTs extracted with 1 exhibit much larger intensity than those extracted with 1,3-phenylene-bridged chiral diporphyrins 2, indicating an improved chiral discrimination ability of 1. In particular, (6,5)-SWNTs display the most intensified CD signals among the SWNTs extracted with 1. In addition, the SWNT extraction ability of 1 has been shown to be considerably enhanced in comparison to 2. These improved discrimination and extraction abilities of 1 are attributed to the formation of its more stable SWNT complex. Computer-calculated energy minimized structures for 1:(6,5)-SWNT complexes show that (R)- and (S)-1 form complexes preferentially with (M)- and (P)-(6,5)-SWNTs, respectively. These calculations also predict that the 1:(6,5)-SWNT complex is approximately 1.6 kcal mol-1 more stable than the corresponding complex of 2, accounting for the improved abilities of 1 in the chiral discrimination and extraction.     

Synthesis of α‐maleimide‐ω‐dienyl heterotelechelic poly(methyl methacrylate) and its cyclization by the intramolecular Diels–Alder reaction

The synthesis of heterotelechelic poly(methyl methacrylate) (PMMA) containing α‐maleimide‐ω‐dienyl end‐groups and its subsequent intramolecular cyclization are described. The anionic polymerization of methyl methacrylate was carried out with 3‐tert‐butyldimethylsilyloxypropyl‐1‐lithium and 5‐bromo‐1,3‐pentadiene as the initiator and terminator, respectively, to synthesize α‐hydroxy‐ω‐dienyl‐PMMA. The introduction of the maleimide group to the α chain end by the reaction of the sodium salt of the polymer with N‐(3‐chloromethylphenyl)‐maleimide or N‐(3‐bromomethylphenyl)‐maleimide was not successful because of the nucleophilic addition of alkoxide to the carbon carbon double bond of the maleimide group. When 4,4′‐bismaleimidediphenylether was allowed to react with the alkoxide, the aimed α‐maleimide‐ω‐dienyl‐PMMA was obtained in a good yield. Ring closure by the intramolecular Diels–Alder reaction was carried out by the heating of the dilute polymer solution in tetrahydrofuran. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 237–246, 2000     

Selective 6-endo cyclization of the acyl radicals onto the nitrogen of imine and oxazoline C-N bonds

Acyl radicals generated by the addition of alkyl or vinyl radicals to carbon monoxide cyclized onto the C-N bonds of imines and oxazoline with perfect 6-endo selectivity, driven by a preference for attack at nitrogen.     

Iron-catalyzed decarbonylation reaction of aliphatic carboxylic acids leading to α-olefins

The catalytic decarbonylation reaction of aliphatic carboxylic acids can be carried out in the presence of an iron complex, and it proceeds smoothly to give α-olefins with high selectivity.     

Vortex dynamics and the Fulde-Ferrell-Larkin-Ovchinnikov state in a magnetic-field-induced organic superconductor

Under special conditions, a superconducting state where the order parameter oscillates in real space, the so-called FFLO state, is theoretically predicted to exist near the upper critical field, as first proposed by Fulde and Ferrell, and Larkin and Ovchinnikov. We report systematic measurements of the interlayer resistance in high magnetic fields to 45 T in the two-dimensional magnetic-field-induced organic superconductor lambda-(BETS)2FeCl4, where BETS is bis(ethylenedithio)tetraselenafulvalene. The resistance is found to show characteristic dip structures in the superconducting state. The results are consistent with pinning interactions between the vortices penetrating the insulating layers and the order parameter of the FFLO state. This gives strong evidence for an oscillating order parameter in real space.