Magnetic order in lightly doped La2-xSrxCuO4

We study long wavelength magnetic excitations in lightly doped La2-xSrxCuO4 (x相似文献   

Magic doping fractions for high-temperature superconductors

We report hole-doping dependence of the in-plane resistivity rho(ab) in a cuprate superconductor La(2-x)Sr(x)CuO4, carefully examined using a series of high-quality single crystals. Our detailed measurements find a tendency towards charge ordering at particular rational hole-doping fractions of 1/16, 3/32, 1/8, and 3/16. This observation appears to suggest a specific form of charge order and is most consistent with the recent theoretical prediction of the checkerboard-type ordering of the Cooper pairs at rational doping fractions x = (2m+1)/2n, with integers m and n.     

Kinetics of water-assisted single-walled carbon nanotube synthesis revealed by a time-evolution analysis

Here we investigate the kinetics of water-assisted CVD (henceforth denoted as supergrowth CVD) by a quantitative time-evolution analysis based on a simple growth model. We found that the supergrowth can be well described by a model where the dynamics of the catalyst activity is treated similar to radioactive decay. An in-depth analysis based on this growth model revealed the kinetics of the supergrowth CVD, showing a scale relationship between the carbon source and water, and elucidated the role of water as a catalyst activity enhancer and preserver.     

Catalytic synthesis of thiobutyrolactones via CO insertion into the C-S bond of thietanes in the presence of a heterodinuclear organoplatinum-cobalt complex

Heterodinuclear organoplatinum-cobalt complex having a 1,2-bis(diphenylphosphino)ethane ligand (dppe)MePt-Co(CO)4 catalyzes CO insertion into the C-S bond of thietanes in THF at 100 degrees C under 1.0 MPa of CO for 2 h to give gamma-thiobutyrolactone in quantitative yield.     

Chirality transfer during alkylation of chiral amides

Chiral amides derived from O-methyl mandelic acid and achiral amines underwent enantioselective alpha-methylation on treatment with LTMP followed by addition of methyl iodide; chirality transfer from an undeprotonated chiral amide into an achiral enolate in a mixed aggregate is supposed to be responsible for the asymmetric induction.     

Anisotropic magnetoresistance in lightly doped La(2)-(x)Sr(x)CuO(4): impact of antiphase domain boundaries on the electron transport

Detailed behavior of the magnetoresistance (MR) is studied in lightly doped antiferromagnetic La(1.99)Sr(0.01)CuO(4), where, thanks to the weak-ferromagnetic moment due to spin canting, the antiferromagnetic (AF) domain structure can be manipulated by the magnetic field. The MR behavior demonstrates that CuO(2) planes indeed contain antiphase AF-domain boundaries in which charges are confined, forming antiphase stripes. The data suggest that a high magnetic field turns the antiphase stripes into in-phase stripes, and the latter appear to give better conduction than the former, which challenges the notion that the antiphase character of stripes facilitates charge motion.     

Specific-heat anomaly caused by ferroelectric nanoregions in Pb(Mg(1/3)Nb(2/3))O3 and Pb(Mg(1/3)Ta(2/3))O3 relaxors

The specific heat of typical relaxors, Pb(Mg(1/3)Nb(2/3))O3 (PMN) and Pb(Mg(1/3)Ta(2/3))O3 (PMT), was measured by adiabatic and relaxation methods between 2 and 420 K. A broad anomaly was found in the specific heat curve over the wide temperature range between 150 and 500 K for PMN, and between 50 and 400 K for PMT, which provides evidence for the formation of ferroelectric nanoregions (FNR) in the paraelectric matrix. The entropy of the anomaly was estimated as 3.3 J K(-1) mol(-1) and 2.9 J K(-1) mol(-1) for PMN and PMT, respectively, which implies an order-disorder-type mechanism for the formation of FNR.     

Change in ionization of barium in calcium and direct determination of barium in calcium by flame atomic absorption spectrometry using the Ba ion resonance line

Partial pressures of barium at various concentrations of calcium are calculated, and degree of ionization of barium in the nitrous oxide-acetylene flame are determined experimentally and theoretically using the Saha equation. The ionization of barium (50 μg ml^?1 ) in the presence of 10000 μg ml^?1 of calcium was about one third of the theoretically expected value. Using the ion resonance line of barium permits the direct determination of barium down to 3 ppm in calcium matrices by atomic absorption spectrophotometry.     

Studies on an enzymatically synthesized antitumor polysaccharide SPR-901

An antitumor polysaccharide SPR-901 was found in a fermented broth of a kind of lactic acid bacteria isolated from rice bran. SPR-901 is a high molecular alpha-glucan and its linkages are almost linear alpha-1,6 glucosidic ones with a small amount (ca. 5%) of branches at C-3 positions. It is a highly purified alpha-glucan and it contains no protein and no inorganic salts. SPR-901 showed significant antitumor activities against murine allogeneic and syngeneic tumors by both intraperitoneal and oral administration, and enhanced carbon clearance ability in mice, while it showed no direct cytotoxicities in vitro. The mechanism of antitumor activities of SPR-901 is supposed to be a host-mediated one, and this substance is classified as one of the biological response modifiers. These properties of SPR-901 were identical to those of RON, which was obtained from rice bran, therefore we concluded that these two polysaccharides were the same substance.