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Total synthesis of (+/-)-1,13-herbertenediol, (+/-)-alpha-herbertenol and (+/-)-beta-herbertenol

Total synthesis of alpha-herbertenol, beta-herbertenol and 1,13-herbertenediol, employing a Claisen rearrangement and ring-closing metathesis as key reactions for the generation of the cyclopentane containing vicinal quaternary carbons, has been described. (C) 2003 Elsevier Science Ltd. All rights reserved.

First-order structural transition in the magnetically ordered phase of Fe(1.13)Te

Specific heat, resistivity, magnetic susceptibility, linear thermal expansion (LTE), and high-resolution synchrotron x-ray powder diffraction investigations of single crystals Fe(1+y) Te (0.06 <= y <= 0.15) reveal a splitting of a single, first-order transition for y <= 0.11 into two transitions for y >= 0.13. Most strikingly, all measurements on identical samples Fe(1.13)Te consistently indicate that, upon cooling, the magnetic transition at T(N) precedes the first-order structural transition at a lower temperature T(s). The structural transition in turn coincides with a change in the character of the magnetic structure. The LTE measurements along the crystallographic c axis display a small distortion close to T(N) due to a lattice striction as a consequence of magnetic ordering, and a much larger change at T(s). The lattice symmetry changes, however, only below T(s) as indicated by powder x-ray diffraction. This behavior is in stark contrast to the sequence in which the phase transitions occur in Fe pnictides.

Magnetic characterization of Co1-xNixFe2O4 (0 <= x <= 1) nanoparticles prepared by co-precipitation route

Magnetic nanoparticles of Ni-doped cobalt ferrite [Co1-xNixFe2O4(0 <= x <= 1)] synthesized by coprecipitation route have been studied as a function of doping concentration (x) and particle size. The size of the particles as determined by X-ray diffractometer (XRD) and transmission electron microscope (TEM) analyses was found in the range 12-48 nm. The coercivity (H-C) and saturation magnetization (M-S) showed a decreasing behavior with increasing Ni concentration. M-S of all the samples annealed at 600 degrees C lies in the range 65.8-13.7 emu/gm. Field-cooled (FC) studies of the samples showed horizontal shift (exchange bias) and vertical shift in the magnetization loop. Strong decrease in exchange bias (H-b) and vertical shift (delta M) was found for low Ni concentrations while negligible decrease was found at higher concentrations. The presence of exchange bias in the low Ni-concentration region has been explained with reference to the interface spins interaction between a surface region (with structural and spin disorder) and a ferrimagnetic core region. M(T) graphs of the samples showed a decreasing trend of blocking temperature (T-b) with increasing Ni concentration. The decrease of T-b with increasing Ni concentration has been attributed to the lower anisotropy energy of Ni+2 ions as compared to Co+2 that increases the probability of the jump across the anisotropy barrier which in turn decreases the blocking temperature of the system.

层状复合氧化物La_4BaCu_(5-x)M_xO_(13+λ)的制备、表征及对CO还原NO的活性

采用柠檬酸爆炸法合成了系列层状钙钛矿型复合氧化物Ｌａ４ＢａＣｕ５ － ｘＭｘＯ１３＋ λ（Ｍ＝ Ｍｎ，Ｃｏ； ｘ＝ ０ ～５） 催化剂． 用ＴＰＤ，ＴＰＲ 和化学分析法对催化剂进行了表征，考察了催化剂在ＣＯ还原ＮＯ 中的催化活性．结果表明，掺杂Ｍｎ，Ｃｏ 后催化剂中的活性氧含量及氧化还原性质发生了变化． 掺杂少量Ｍｎ，Ｃｏ 可使催化剂在ＣＯ 还原ＮＯ中的催化活性明显提高，且掺杂Ｃｏ 的样品比掺杂Ｍｎ 的样品活性提高更明显．这是由于ＣｕＭｎ 与ＣｕＣｏ 之间的协同作用不同导致的结果.