555 research outputs found
Bis(μ-3-hydroxyÂbenzoato)-κ2 O 1:O 3;κ2 O 3:O 1-bisÂ[bisÂ(1H-benzimidazole-κN 3)(3-hydroxyÂbenzoato-κO)nickel(II)] bisÂ(1H-benzimidazole-κN 3)bisÂ(3-hyÂdroxyÂbenzoato-κO 1)nickel(II) hexaÂhydrate
The title compound, [Ni2(C7H5O3)4(C7H6N2)4][Ni(C7H5O3)2(C7H6N2)2]·6H2O, is a mononuclear/dinuclear nickel(II) cocrystal, the two molÂecular species interÂacting through hydrogen bonds that involve the uncoordinated water molÂecules. In the mononuclear species, the NiII ion, located on an inversion center, is coordinated by two 1H-benzimidazole (bzim) ligands and two 3-hydroxyÂbenzoate (hba) anions in a square-planar geometry. In the centrosymmetric dinuclear species, the NiII ion is coordinated by two bzim ligands and three hba anions in a square-pyramidal geometry; of the two independent hba anions, one bridges two NiII ions with both carboxylate and hydroxyl groups whereas the other coordinÂates in a unidentate manner to the NiII ion. The apical Ni—OhydroxÂyl bond is 0.39 Å longer than the basal Ni—OcarboxÂyl bonds. The face-to-face separation of 3.326 (9) Å indicates the existence of π–π stacking between parallel bzim ligands of adjacent dinuclear entities. Extensive N—H⋯O and O—H⋯O hydrogen bonds help to stabilize the crystal structure
New application of decomposition of U(1) gauge potential:Aharonov-Bohm effect and Anderson-Higgs mechanism
In this paper we study the Aharonov-Bohm (A-B) effect and Anderson-Higgs
mechanism in Ginzburg-Landau model of superconductors from the perspective of
the decomposition of U(1) gauge potential. By the Helmholtz theorem, we derive
exactly the expression of the transverse gauge potential in A-B
experiment, which is gauge-invariant and physical. For the case of a bulk
superconductor, we find that the gradient of the total phase field
provides the longitudinal component , which reflects the
Anderson-Higgs mechanism. For the case of a superconductor ring, the gradient
of the longitudinal phase field provides the longitudinal component
, while the transverse phase field produces
new physical effects such as the flux quantization inside a superconducting
ring.Comment: 6 pages, no figures, final version to appear in Modern Physics
Letters
First-principles prediction of coexistence of magnetism and ferroelectricity in rhombohedral Bi2FeTiO6
First principles calculations based on the density functional theory within
the local spin density approximation plus U(LSDA+U)scheme, show rhombohedral
BiFeTiO is a potential multiferroic in which the magnetism and
ferroelectricity coexist . A ferromagnetic configuration with magnetic moment
of 4 per formula unit have been reported with respect to the minimum
total energy. Spontaneous polarization of 27.3 C/cm, caused mainly by
the ferroelectric distortions of Ti, was evaluated using the berry phase
approach in the modern theory of polarization. The Bi-6s stereochemical
activity of long-pair and the `d-ness' criterion in off-centring of Ti were
coexisting in the predicted new system. In view of the oxidation state of
Bi,Fe,Ti, and O from the orbital-resolved density
of states of the Bi-6p, Fe-3d,Ti-3d, and O-2p states,the valence state of
BiFeTiO in the rhombohedral phase was found to be
BiFeTiO.Comment: 22 pages, 9 figures. submitted to Physics Letters
Mitochondrial matR sequences help to resolve deep phylogenetic relationships in rosids
<p>Abstract</p> <p>Background</p> <p>Rosids are a major clade in the angiosperms containing 13 orders and about one-third of angiosperm species. Recent molecular analyses recognized two major groups (i.e., fabids with seven orders and malvids with three orders). However, phylogenetic relationships within the two groups and among fabids, malvids, and potentially basal rosids including Geraniales, Myrtales, and Crossosomatales remain to be resolved with more data and a broader taxon sampling. In this study, we obtained DNA sequences of the mitochondrial <it>matR </it>gene from 174 species representing 72 families of putative rosids and examined phylogenetic relationships and phylogenetic utility of <it>matR </it>in rosids. We also inferred phylogenetic relationships within the "rosid clade" based on a combined data set of 91 taxa and four genes including <it>matR</it>, two plastid genes (<it>rbcL</it>, <it>atpB</it>), and one nuclear gene (18S rDNA).</p> <p>Results</p> <p>Comparison of mitochondrial <it>matR </it>and two plastid genes (<it>rbcL </it>and <it>atpB</it>) showed that the synonymous substitution rate in <it>matR </it>was approximately four times slower than those of <it>rbcL </it>and <it>atpB</it>; however, the nonsynonymous substitution rate in <it>matR </it>was relatively high, close to its synonymous substitution rate, indicating that the <it>matR </it>has experienced a relaxed evolutionary history. Analyses of our <it>matR </it>sequences supported the monophyly of malvids and most orders of the rosids. However, fabids did not form a clade; instead, the COM clade of fabids (Celastrales, Oxalidales, Malpighiales, and Huaceae) was sister to malvids. Analyses of the four-gene data set suggested that Geraniales and Myrtales were successively sister to other rosids, and that Crossosomatales were sister to malvids.</p> <p>Conclusion</p> <p>Compared to plastid genes such as <it>rbcL </it>and <it>atpB</it>, slowly evolving <it>matR </it>produced less homoplasious but not less informative substitutions. Thus, <it>matR </it>appears useful in higher-level angiosperm phylogenetics. Analysis of <it>matR </it>alone identified a novel deep relationship within rosids, the grouping of the COM clade of fabids and malvids, which was not resolved by any previous molecular analyses but recently suggested by floral structural features. Our four-gene analysis supported the placements of Geraniales, Myrtales at basal nodes of the rosid clade and placed Crossosomatales as sister to malvids. We also suggest that the core part of rosids should include fabids, malvids and Crossosomatales.</p
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