The time evolution of the thermal bleaching of the long-lived, photogenerated midgap absorption band in a PtCl chain compound is examined in a temperature range 220 -330 K. The long-lived absorption arises from kinks each confined in a segment of the PtCl chain by energy barriers of the order of 0.5 eV. Because of a random distribution of the barrier height the pair coalescence decay shows a ln t dependence at all temperatures in the experimental range, 0-60 min, of time t after discontinuation of laser pumping. [S0031-9007(97)04131-8] PACS numbers: 71.45.Lr, 61.72.Cc, 61.80.Ba, 78.47. + p Measurements of time-resolved optical response provide a wealth of information on the relaxation processes of self-localized excited states in low-dimensional systems. An ultrafast pump-and-probe measurement of absorption in cis-and trans-polyacetylene, for instance, has revealed that the decay of the photogenerated polaronic and solitonic kinks is dominated by their collision in the course of random walks [1]. A similar experiment on an MX chain compound has shown that the kinks created by a short light pulse have a lifetime of the order of 1-10 ps [2]. According to a photoluminescence measurement on a different MX chain compound [3], the lifetime of the charge-transfer (CT) excitons, which is of the order of 100 ps, has a unique temperature dependence that is suggestive of the presence of a relaxation channel of a CT exciton into a soliton pair.The MX chain compounds consist of chainwise M-X bonds showing a charge-density-wave (CDW) state of M (Pt or Pd) ions. If the CDW state is ordered in one dimension only, the twofold degeneracy of the valence alternation allows the chains to support solitonic kinks as well as polaronic ones [4,5]. The PtCl chain compounds, ͓Pt͑en͒ 2 ͔ ͓Pt͑en͒ 2 Cl 2 ͔ ͑ClO 4 ͒ 4 and ͓Pt͑en͒ 2 ͔ ͓Pt͑en͒ 2 Cl 2 ͔ ͑BF 4 ͒ 4 , belong to this category, where (en) signifies the ethylenediamine molecule. The photoluminescence study reported in Ref.[3] is concerned with the former compound. The two substances are very similar in the basic properties of the Pt-Cl chain bonds. In fact, in both substances the optical reflection spectrum at the fundamental Peierls gap, i.e., the CT transition between d z orbitals of Pt 21 and Pt 41 ions, peaks around 2.8 eV [6], while a photosensitive midgap band (so-called A band) due to self-localized kinks appears around 1.65 eV [7,8]. Both the CT and A bands are optically allowed only for the polarization E k b [4], where E and b are the electric field of light and the Pt-Cl chain axis of the crystal, respectively.In this Letter we study the decay behavior of the A band generated by a steady pumping of the CT exciton in the BF 4 salt. Until now time-resolved studies in onedimensional solids have primarily focused on photoexcitation dynamics in ultrafast time scales. In contrast the photogenerated A band in the above-mentioned PtCl chain compounds has an exceedingly long decay time. Since its photoenhancement effect was discovered, the decay time has been recognized to be much...
The N recovery from 15N‐labeled swine manure compost and rice bran with or without simultaneous application of unlabeled cattle manure compost was examined in a paddy field with direct‐seeded rice during a 1‐year period (1 crop season). In all the 15N‐labeled materials including (15NH4)2SO4, the processes of N recovery from the 15N materials by rice plants were different between the plots with and without application of cattle manure compost. At the tillering stage, the N recovery rates from the 15N materials in the plots with application of cattle manure compost were significantly lower than those in the plots without application of cattle manure compost. These recovery rates, however, became close and no significant differences were observed at the maturity stage. Thus, simultaneous application of cattle manure compost could impede the N recovery from swine manure compost, rice bran as well as (NH4)2SO4.
Methanogenic archaea are strict anaerobes and demand highly reduced conditions to produce methane in paddy field soil. However, methanogenic archaea survive well under upland and aerated conditions in paddy fields and exhibit stable community. In the present study, methanogenic archaeal community was investigated in fields where paddy rice (Oryza sativa L.) under flooded conditions was rotated with soybean (Glycine max [L.] Merr.) under upland conditions at different rotation histories, by polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) and real-time quantitative PCR methods targeting 16S rRNA and mcrA genes, respectively. Soil samples collected from the fields before flooding or seeding, during crop cultivation and after harvest of crops were analyzed. The abundance of the methanogenic archaeal populations decreased to about one-tenth in the rotational plots than in the consecutive paddy (control) plots. The composition of the methanogenic archaeal community also changed. Most members of the methanogenic archaea consisting of the orders Methanosarcinales, Methanocellales, Methanomicrobiales, and Methanobacteriales existed autochthonously in both the control and rotational plots, while some were strongly affected in the rotational plots, with fatal effect to some members belonging to the Methanosarcinales. This study revealed that the upland conversion for one or longer than 1 year in the rotational system affected the methanogenic archaeal community structure and was fatal to some members of methanogenic archaea in paddy field soil.
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