BCC铁中刃型位错与铜沉淀物相互作用的原子尺度模拟

为了从原子尺度弄清楚因辐射损伤而出现的第二相铜沉淀物对位错运动状况的影响,在Osetsky模型和Malerba势能基础上,通过共轭梯度法进行能量最小化,对BCC铁中刃型位错与铜沉淀物的相互作用进行了模拟.再现作用过程的同时,重点探讨了铜沉淀物直径、间距等因素对相互作用的影响,并将模拟结果与连续体理论模型进行了对比分析.结果表明:铜沉淀物直径越大,相互作用越强,位错越难越过沉淀物.而铜沉淀物间距越大,位错越容易越过沉淀物,Malerba势能下的模拟结果相比Ackland势能下的模拟结果与连续体理论模型结果相符得更好.     

CLINICAL MAGNETIC RESONANCE VOLUMETRY OF THE HIPPOCAMPUS IN 58 EPILEPTIC DOGS*

Hippocampal atrophy, which is a component of hippocampal sclerosis and recognized commonly in human intractable epilepsy, is controversial in canine epilepsy. We examined the hippocampal volume in 58 epileptic dogs and 35 control dogs using magnetic resonance (MR) images, and calculated the relative hippocampal volume asymmetry of the right and left hippocampus. Subjectively, there were visible MR imaging abnormalities in seven of the 58 epileptic dogs (12%). The hippocampel volume asymmetric ratio of epileptic dogs (5.84±4.47%) was significantly greater than that of control dogs (1.62±0.88%). Using a cutoff threshold asymmetric ratio of 6% that is indicated in human epilepsy, 28 epileptic dogs (48%) were characterized as having unilateral hippocampus atrophy. The hippocampal volume asymmetry ratio cannot be used to detect bilateral atrophy. In conclusion, although less frequent than that observed in human epilepsy patients, hippocampal atrophy may occur in canine epilepsy.     

Distribution patterns of leptocephali in the Kuroshio–Oyashio transitional region of the western North Pacific

Leptocephalus assemblages and distribution patterns were studied in the Kuroshio–Oyashio transitional region of the western North Pacific. A total of 479 leptocephali, representing at least 21 species (types) including eight undescribed types, were collected during a cruise of the T/V Hokuho Maru from 8 to 30 May 2002. The most abundant leptocephali were the congrids Gnathophis nystromi nystromi and Gnathophis nystromi ginanago. The assemblages at each station were clustered into four groups (one group in the Kuroshio region and three in the transition zone) using the ordination and the fuzzy c‐means method based on species composition similarities between stations. Each leptocephalus species was also clustered by the same method into one of three groups. The first group had the greatest numbers of species and mainly occurred at the station group in the Kuroshio region, sharing a similar distribution to G. n. nystromi. The second group had the greatest abundance, especially in the transition zone, but contained only one species, G. n. ginanago, which also occurred at all stations. Moreover discrimination of station groups in the transition zone corresponded well with the assemblage pattern of this species group. The last species group comprised rare and low abundance species. Most leptocephali in the study area were reported from the Kuroshio upstream region, so the discrimination of leptocephali assemblages in the study area may reflect their different ecology. Furthermore, the analytical methods used in this study yielded more meaningful and clearer groups than the other usual methods, validating application of this analysis to complex areas such as the transition zone.     

Observations on the effect of salinity and photon fluence rate on the induction of sporulation and rhizoid formation in the green alga Enteromorpha prolifera (Müller) J. Agardh (Chlorophyta, Ulvales)

ABSTRACT: Although most members of the genus Enteromorpha are important edible green algae, some species are also potentially economically valuable crops. Samples of E. prolifera were obtained from the Yoshino River estuary, Tokushima, Japan and cultured in laboratory conditions at 10°C, a salinity of 20 psu, under white light with 12 h light : 12 h dark cycle and at a photon fluence rate (PFR) of 40 μmol/m² per s for 30 days. In the present study, the effect of salinity and PFR on the induction of reproductive cells and rhizoid formation were investigated. Synchronous formation of swarmers by thalli was induced in excised disks of 1.2 mm diameter after 2–5 days incubation. The optimum salinity for maturation of reproductive cells was between 5.0 and 52.0 psu, and between 13.2 and 45.3 psu for swarmer release, although the lower limit for swarmer release was 5.0 psu. Maturation of reproductive cells and swarmer release required a PFR higher than 16 μmol/m² per s. The minimum PFR for swarmer release was 8 μmol/m² per s. Many rhizoids were formed between 1.6 and 52.0 psu and photon fluence rates between 8 and 320 μmol/m² per s. Rhizoids were formed in a polarized manner.     

Plant growth inhibitors: Patchoulane-type sesquiterpenes from Cyperus rotundus L.

Two sesquiterpene ketones, cyperotundone and α-cyperone, were isolated from dried tubers of purple nutsedge ( Cyperus rotundus L.) as major constituents: ≈0.26% and 0.1% of dried tuber, respectively. These allelochemicals affect plant growth, but we consider that these terpenoids undergo modification when they are released into the rhizosphere from the donor plant. For the structure–activity relationship study, cyperotundone was oxidized with selenium dioxide in acetic acid to 4-patchoulene-2,3-dione and 4-patchoulene-2,3,6-trione. Subsequent hydrogenation of 4-patchoulene-2,3-dione and 4-patchoulene-2,3,6-trione gave hydroxylated derivatives, cyperotundon-2-ol and 3-hydroxy-4-patchoulene-2,6-dione, respectively. 4-Patchoulene-2,3-dione inhibited the hypocotyl growth of lettuce seedlings but promoted radicle elongation at 0.1−2 mg L⁻¹ concentration without chlorosis. Moreover, this radicle elongation recovered with the addition of galactose and was not antagonized by gibberellin A₃. The effect of 4-patchoulene-2,3,6-trione showed a similar chlorosis, caused by 3,6,9-sugetriol triketone, against lettuce seedlings. These ketones did not show the radicle elongation.