排序方式: 共有60条查询结果,搜索用时 281 毫秒
31.
Baran P Boca R Chakraborty I Giapintzakis J Herchel R Huang Q McGrady JE Raptis RG Sanakis YO Simopouloso A 《Inorganic chemistry》2008,47(2):645-655
A one-pot synthetic procedure yields the octanuclear Fe(III) complexes Fe(8)(micro(4-)O)(4)(micro-pz(*))(12)X(40, where X = Cl and pz(*) = pyrazolate anion (pz = C(3)H(3)N(2)-) (1), 4-Cl-pz (2), and 4-Me-pz (3) or X = Br and pz(*) = pz (4). The crystal structures of complexes 1-4, determined by X-ray diffraction, show an Fe(4)O(4)-cubane core encapsulated in a shell composed of four interwoven Fe(micro-pz(*))(3)X units. Complexes 1-4 have been characterized by 1H NMR, infrared, and Raman spectroscopies. M?ssbauer spectroscopic analysis distinguishes the cubane and outer Fe(III) centers by their different isomer shift and quadrupole splitting values. Electrochemical analyses by cyclic voltammetry show four consecutive, closely spaced, reversible reduction processes for each of the four complexes. Magnetic susceptibility studies, corroborated by density functional theory calculations, reveal weak antiferromagnetic coupling among the four cubane Fe centers and strong antiferromagnetic coupling between cubane and outer Fe atoms of 1. The structural similarity between the antiferromagnetic Fe(8)(micro(4-)O)(4) core of 1-4 and the antiferromagnetic units contained in the minerals ferrihydrite and maghemite is demonstrated by X-ray and M?ssbauer data. 相似文献
32.
G. Boca D. Levinthal F. Lopez C. Georgiopoulos H. Goldman S. Hagopian V. Hagopian K. F. Johnson J. Streets K. Streets H. B. White M. Crisler A. Lathrop S. Pordes M. Cummings H. R. Gustafson 《Zeitschrift fur Physik C Particles and Fields》1991,49(4):543-553
The average fraction, , of jet momentum carried by the associated charged leading hadron has been determined in the reactionp+N→h 1+h 2+X whereN is the target nucleon;h 1,h 2 are the leading particles of two jets produced at highP ⊥. An 800 GeV/c proton beam and 4 nuclear targets: Be, Al, Fe and W were used. The distributions agree with the QCD-parton model predictions for single independent protonnucleon scattering and independent fragmentation process. 相似文献
33.
Boiocchi M Del Boca L Esteban-Gómez D Fabbrizzi L Licchelli M Monzani E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(10):3097-3104
The urea-based receptor 1 (1-(7-nitrobenzo[1,2,5]oxadiazol-4-yl)-3-(4-nitrophenyl)urea, L--H), interacts with X- ions in MeCN, according to two consecutive steps: 1) formation of a hydrogen-bond complex [L--H...X]-; 2) deprotonation of L--H to give L- and [HX2]-, as shown by spectrophotometric and 1H NMR titration experiments. Step 2) takes place with more basic anions (fluoride, carboxylates, dihydrogenphosphate), while less basic anions (Cl-, NO2-, NO3-) do not induce proton transfer. On crystallisation from a solution containing L--H and excess Bu4NF, the tetrabutylammonium salt of the deprotonated urea derivative (Bu4N[L]) was isolated and its crystal and molecular structure determined. 相似文献
34.
A phylogenomic reconstruction of the protein world based on a genomic census of protein fold architecture 总被引:1,自引:0,他引:1
Minglei Wang Simina Maria Boca Rakhee Kalelkar Jay E. Mittenthal Gustavo Caetano‐Anolls 《Complexity》2006,12(1):27-40
The protein world has a hierarchical and redundant organization that can be specified in terms of evolutionary units of molecular structure, the protein domains. The Structural Classification of Proteins (SCOP) has unified domains into a comparatively small set of folding architectures, the protein fold families and superfamilies, and these have been further grouped into protein folds. In this study, we reconstruct the evolution of the protein world using information embedded in a structural genomic census of fold architectures defined by a phylogenomic analysis of 185 completely sequenced genomes using advanced hidden Markov models and 776 folds described in SCOP release 1.67. Our study confirms the existence of defined evolutionary patterns of architectural diversification and explores how phylogenomic trees generated from folds relate to those reconstructed from fold superfamilies. Evolutionary patterns help us propose a general conceptual model that describes the growth of architectures in the protein world. © 2006 Wiley Periodicals, Inc. Complexity 12: 27–40, 2006 相似文献
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36.
On the index of Farey sequences 总被引:1,自引:0,他引:1
Boca Florin P.; Zaharescu Alexandru; Gologan Radu N. 《Quarterly Journal of Mathematics》2002,53(4):377-391
37.
Adam J Bai X Baldini AM Baracchini E Bemporad C Boca G Cattaneo PW Cavoto G Cei F Cerri C de Bari A De Gerone M Doke T Dussoni S Egger J Fratini K Fujii Y Galli L Gallucci G Gatti F Golden B Grassi M Grigoriev DN Haruyama T Hildebrandt M Hisamatsu Y Ignatov F Iwamoto T Kettle PR Khazin BI Kiselev O Korenchenko A Kravchuk N Maki A Mihara S Molzon W Mori T Mzavia D Natori H Nicolò D Nishiguchi H Nishimura Y Ootani W Panareo M Papa A Pazzi R Piredda G Popov A Renga F Ritt S Rossella M Sawada R 《Physical review letters》2011,107(17):171801
We present a new result based on an analysis of the data collected by the MEG detector at the Paul Scherrer Institut in 2009 and 2010, in search of the lepton-flavor-violating decay μ(+)e(+)γ. The likelihood analysis of the combined data sample, which corresponds to a total of 1.8×10(14) muon decays, gives a 90% C.L. upper limit of 2.4×10(-12) on the branching ratio of the μ(+)→e(+)γ decay, constituting the most stringent limit on the existence of this decay to date. 相似文献
38.
Monatshefte für Mathematik - We study analogues of Minkowski’s question mark function ?(x) related to continued fractions with even or with odd partial quotients. We prove that these... 相似文献
39.
We demonstrate the reversible mapping of a coherent state of light with a mean photon number (-)n approximately equal to 1.1 to and from the hyperfine states of an atom trapped within the mode of a high-finesse optical cavity. The coherence of the basic processes is verified by mapping the atomic state back onto a field state in a way that depends on the phase of the original coherent state. Our experiment represents an important step toward the realization of cavity QED-based quantum networks, wherein coherent transfer of quantum states enables the distribution of quantum information across the network. 相似文献
40.
Herchel R Boca R Gembický M Falk K Fuess H Haase W Svoboda I 《Inorganic chemistry》2007,46(5):1544-1546
The Schiff condensation of 2-pyridinecarboxaldehyde N-oxide with 2-aminophenol gave a tridentate ligand, abbreviated as Hpoxap. This ligand bears the functionality of a terminating group in a trinuclear complex [Mn(poxap)Mn(ac)4Mn(poxap)], where ac- is the acetate bridge. The magnetic data were treated simultaneously during the fitting procedure with the spin Hamiltonian containing isotropic exchange, the zero-field splitting parameters, and the molecular-field correction and resulted in JMn-Mn/hc = -4.73 cm-1, gMn(t) = 1.96, DMn(t)/hc = -0.45 cm-1, and zj/hc = +0.45 cm-1 with ground state S = 5/2, where t = terminal atom. At low temperature, the features of a ferromagnetic correlation become evident. 相似文献