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41.
In order to interpret abrupt changes of distributions of orientations andmagnitudes of hyperfine fields in Mössbauer measurements of57Fe in YFeMnO4, a model is proposed. The origin is assumed to be not static but dynamic. Fluctuating fields are caused by spins in a fully frustrated spin system, namely, a Heisenberg spin system on a triangular lattice in a two-dimensional antiferromagnet. Extending the stochastic theory for the fluctuation between two states to that among many states with a Gaussian distribution, we fit the spectra with three parameters, hyperfine fieldH
hf, correlation time c, andwidth of fluctuating field , within a limited condition of =c=1. Obtained results represent the characteristic features of Mössbauer spectra well, in spite of a simplified model. 相似文献
42.
Isozaki T Fujikawa T Takezoe H Fukuda A Hagiwara T Suzuki Y Kawamura I 《Physical review. B, Condensed matter》1993,48(18):13439-13450
43.
It is known that for simple arrangements in thed-dimensional Euclidean spaceR
d
The average number ofj-dimensional subfaces of ak-dimensional face is less than
. In this paper, we show that this is also true for all arrangements inR
d
and for all oriented matroids, and we give combinatorial proofs. 相似文献
44.
Four possible diastereomers of pentenocin B were synthesized in a stereocontrolled manner, and the first total synthesis of a natural enantiomer of (+)-pentenocin B unequivocally established the absolute stereochemistry to be 4S,5R,6R. 相似文献
45.
46.
The delta form of crystalline syndiotactic polystyrene is a clathrate molecular compound in which various aromatic molecules are encaged. We have investigated the size, shape, and connectivity of the molecular cavity in the crystal using a molecular dynamics simulation. The effects of the guest species on the cavity structure were investigated in detail. In order to systematically vary the guest structure, various aromatic guests, e.g., benzene, toluene, p-xylene, m-xylene, o and mesitylene were examined. The interstitial spaces between the guests and the polymer chains were analyzed by cluster analysis of the free volumes. The individual cavity volumes into which the guests are clathrated were also evaluated. It was found that the guest molecules can greatly affect not only the cavity size and shape but also the connectivity of the cavities. The transport of small molecules in the crystal is discussed in connection with the cavity structure. 相似文献
47.
Tetsuo Suami Hiroaki Sasai Kazuhiro Matsuno Nobuo Suzuki Yoshimasa Fukuda Osamu Sakanaka 《Tetrahedron letters》1984,25(40):4533-4536
Tunicamycins and their eight analogs have been synthesized by condensation of a N-acetyl-D-glucosamine derivative and an anomeric chloride of tunicaminyl uracil, followed by deprotections and N-acylation. 相似文献
48.
Two new phenolic compounds, glicoricone (3) and licofuranone (4), were isolated from a species of licorice brought from the northwestern region of China, and their structures were assigned. Among the twelve licorice constituents examined for the inhibition of monoamine oxidase (MAO), six compounds, 3, 4, genistein (6), licopyranocoumarin (7), licocoumarone (14) and glycyrrhisoflavone (15), inhibited the enzyme with the IC50 (concentration required for 50% inhibition of the enzyme activity) values of 6.0 x 10(-5)-1.4 x 10(-4) M. Glycyrrhizin (1) also inhibited MAO with the IC50 value of 1.6 x 10(-4) M. 相似文献
49.
Norio Miyoshi Kiyoaki Hara Issei Yokoyama Giiti Tomita Masaru Fukuda 《Photochemistry and photobiology》1988,47(5):685-688
Abstract— The absorption and fluorescence spectra, and the fluorescence lifetime of acridine orange (AO) were measured in a wide range of the sodium dodecyl sulfate (SDS) concentration below and above the critical micelle concentration (cmc). The fluorescence consisted of two components with different lifetimes; short (<3 ns) and long (>3 ns). The short and long lifetime components are attributed to the AO monomer and dimer associated with detergent, respectively. The lifetime of the dimer increased with increasing the SDS concentration just below the cmc. It decreased suddenly to a constant value just above the cmc. The lifetime of the monomer showed only a slight increase in the concentration range of SDS employed. 相似文献
50.
The stability constants of the ternary complexes containing UTP, 2,2′-bipyridyl (bipy), and Co2+, Ni2+, Cu2+, or Zn2+ (M2+) have been determined by potentiometric titrations (Table 1). Changes in stability are quantified by Δlog KM = log K–log K. For the Co2+, Ni2+, Cu2+, and Zn2+ systems Δlog KM is 0.10, ?0.13, 0.36, and 0.15, respectively. All these ternary complexes are considerably more stable than would be expected on statistical grounds; indeed, for Co2+, Cu2+, and Zn2+, UTP4? binds more tightly to M (bipy)2+ than to M2+. An UV. difference spectroscopic study suggests that stacked adducts between bipyridyl and the pyrimidine moiety of uridine are formed. 1H-NMR. studies of the bipy/uridine, bipy/UTP, and bipy/UTP/Zn2+ systems (Figs. 1 and 2) confirm the presence of stacking in the binary adducts and in the ternary complex. There is also evidence for the existence of the stacked protonated complex, Zn(bipy) (HUTP)?, with the proton at the γ-phosphate group. The acidity constant of this ternary complex has been measured (Fig. 3). The observed stability enhancement of stacked adducts by the formation of a metal ion bridge is discussed (Fig. 4) and biological implications are indicated. 相似文献