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131.
Phase transitions in MgAl2O4 were examined at 21-27 GPa and 1400-2500 °C using a multianvil apparatus. A mixture of MgO and Al2O3 corundum that are high-pressure dissociation products of MgAl2O4 spinel combines into calcium-ferrite type MgAl2O4 at 26-27 GPa and 1400-2000 °C. At temperature above 2000 °C at pressure below 25.5 GPa, a mixture of Al2O3 corundum and a new phase with Mg2Al2O5 composition is stable. The transition boundary between the two fields has a strongly negative pressure-temperature slope. Structure analysis and Rietveld refinement on the basis of the powder X-ray diffraction profile of the Mg2Al2O5 phase indicated that the phase represented a new structure type with orthorhombic symmetry (Pbam), and the lattice parameters were determined as a=9.3710(6) Å, b=12.1952(6) Å, c=2.7916(2) Å, V=319.03(3) Å3, Z=4. The structure consists of edge-sharing and corner-sharing (Mg, Al)O6 octahedra, and contains chains of edge-sharing octahedra running along the c-axis. A part of Mg atoms are accommodated in six-coordinated trigonal prism sites in tunnels surrounded by the chains of edge-sharing (Mg, Al)O6 octahedra. The structure is related with that of ludwigite (Mg, Fe2+)2(Fe3+, Al)(BO3)O2. The molar volume of the Mg2Al2O5 phase is smaller by 0.18% than sum of molar volumes of 2MgO and Al2O3 corundum. High-pressure dissociation to the mixture of corundum-type phase and the phase with ludwigite-related structure has been found only in MgAl2O4 among various A2+B3+2O4 compounds. 相似文献
132.
Benjamin Nabet Naomi E. Leonard Iain D. Couzin Simon A. Levin 《Journal of Nonlinear Science》2009,19(4):399-435
We analyze a continuous-time model of a multi-agent system motivated by simulation studies on dynamics of decision making
in animal groups in motion. Each individual moves at constant speed in the plane and adjusts its heading in response to relative
headings of others in the population. The population includes two subgroups that are “informed” such that individuals in each
subgroup have a preferred direction of motion. The model exhibits fast and slow time scales allowing for a reduction in the
dimension of the problem. The stable solutions for the reduced model correspond to compromise by individuals with conflicting
preferences. We study the global phase space for the proposed reduced model by computing equilibria and exploring stability
and bifurcations.
B. Nabet’s and N.E. Leonard’s work is supported in part by AFOSR grant FA9550-07-1-0-0528 and ONR grants N00014-02-1-0826
and N00014-04-1-0534.
I.D. Couzin’s work was supported by the Royal Society, Balliol College and EPSRC grants GR/S04765/01 and GR/T11234/01, a Searle
Scholar Award and DARPA grant HR001-05-1-0057.
S.A. Levin’s work was supported in part by DARPA grant HR0011-05-1-0057 and NSF grant EF-0434319. 相似文献
133.
Sakai N Kamikawa Y Nishii M Matsuoka T Kato T Matile S 《Journal of the American Chemical Society》2006,128(7):2218-2219
The self-assembly of folate dendrimers into pi-stacked supramolecular rosettes is shown to produce ion channels in planar and spherical lipid bilayer membranes. The found ion channels are small, quite homogeneous, long-lived, ohmic, cation selective (Eisenman I), and blockable by the permeant cation. 相似文献
134.
A method for direct palladium-catalyzed N-arylation reaction of nucleobases was developed for the convenient synthesis of DNA adducts with carcinogenic compounds. Using xantphos as the phosphine ligand and tetraethylammonium fluoride as the base in DMSO, several o-iodonitroarenes could be efficiently coupled with 2'-deoxyguanosine, 2'-deoxyadenosine, and 2'-deoxycytidine. The presence of a 3'-phosphate group in the deoxyribose moiety was found to be compatible with this N-arylation reaction; further, oligonucleotides could serve as substrates. The facile nitroreduction of the coupling compounds (12) yielded 2'-deoxyguanosin-N2-ylarylamine adducts, which are known to be biologically important. Compound 12 was easily converted to phosphoramidite derivatives, allowing the preparation of site-specific modified oligonucleotides with arylamine after the nitroreduction. 相似文献
135.
Yamada M Wakahara T Lian Y Tsuchiya T Akasaka T Waelchli M Mizorogi N Nagase S Kadish KM 《Journal of the American Chemical Society》2006,128(5):1400-1401
The mapping of bond connectivity in the carbon cage of [Ce@C82]- and full assignment of the NMR lines were successfully achieved by means of 2D INADEQUATE NMR measurement. Paramagnetic NMR analysis shows that the Ce atom in [Ce@C82]- is located at an off-centered position adjacent to a hexagonal ring along the C2 axis of the C2v-C82 cage. 相似文献
136.
137.
Kurihara H Lu X Iiduka Y Nikawa H Mizorogi N Slanina Z Tsuchiya T Nagase S Akasaka T 《Journal of the American Chemical Society》2012,134(6):3139-3144
Little is known about the chemical properties of carbide cluster metallofullerenes (CCMFs). Here we report the photochemical reaction of a newly assigned CCMF Sc(2)C(2)@C(2v)(5)-C(80) with 2-adamantane-2,3-[3H]-diazirine (AdN(2), 1), which provides a carbene reagent under irradiation. Five monoadduct isomers (2a-2e), with respective abundances of 20%, 40%, 25%, 5%, and 10%, were isolated and characterized with a combination of experimental techniques including unambiguous single-crystal X-ray crystallography. Results show that the two Sc atoms of the bent Sc(2)C(2) cluster tend to move in most cases, whereas the C(2)-unit is almost fixed. Accordingly, it is difficult to explain the addition patterns by considering the strain and charge density on the cage with a fixed cluster, and thus a moving cluster may account for the addition patterns. These results show that the situation of CCMFs is more complicated than those in other metallofullerenes. Furthermore, a thermal isomerization process from 2b to 2c was observed, confirming that the most abundant isomer 2b is a kinetically favored adduct. Finally, it is revealed that the electronic and electrochemical properties of pristine Sc(2)C(2)@C(2v)(5)-C(80) have been markedly altered by exohedral modification. 相似文献
138.
139.
Suzuki M Kawamura N Miyagawa H Garitaonandia JS Yamamoto Y Hori H 《Physical review letters》2012,108(4):047201
We show that bulk gold (Au) exhibits temperature-independent paramagnetism in an external magnetic field by x-ray magnetic circular dichroism spectroscopy at the Au L(2) and L(3) edges. Using the sum-rule analysis, we obtained a magnetic moment of 1.3 × 10(-4) μB/atom in an external magnetic field of 10 T and a paramagnetic susceptibility of 8.9 × 10(-6) for the 5d orbit. The induced paramagnetism in bulk Au is characterized by a large (≈ 30%) orbital contribution. This orbital component was retained even when Au atoms formed nanoparticles, playing an important role in stabilizing the spontaneous spin polarization in the Au nanoparticles. 相似文献
140.
NB Croghan KH Arehart JM Kates 《The Journal of the Acoustical Society of America》2012,132(2):1177-1188
Dynamic-range compression (DRC) is used in the music industry to maximize loudness. The amount of compression applied to commercial recordings has increased over time due to a motivating perspective that louder music is always preferred. In contrast to this viewpoint, artists and consumers have argued that using large amounts of DRC negatively affects the quality of music. However, little research evidence has supported the claims of either position. The present study investigated how DRC affects the perceived loudness and sound quality of recorded music. Rock and classical music samples were peak-normalized and then processed using different amounts of DRC. Normal-hearing listeners rated the processed and unprocessed samples on overall loudness, dynamic range, pleasantness, and preference, using a scaled paired-comparison procedure in two conditions: un-equalized, in which the loudness of the music samples varied, and loudness-equalized, in which loudness differences were minimized. Results indicated that a small amount of compression was preferred in the un-equalized condition, but the highest levels of compression were generally detrimental to quality, whether loudness was equalized or varied. These findings are contrary to the "louder is better" mentality in the music industry and suggest that more conservative use of DRC may be preferred for commercial music. 相似文献