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61.
We prove that there exists a 1-convex surface whose universal covering does not satisfy the discrete disk property. 相似文献
62.
Renzo Caddeo Stefano Montaldo Cezar Oniciuc Paola Piu 《Mediterranean Journal of Mathematics》2006,3(3-4):449-465
In this article we consider the Euler-Lagrange method associated to a suitable bilagrangian to study biharmonic curves of
a Riemannian manifold. We apply this method to characterize biharmonic curves of the three-dimensional Lie group Sol. We also
classify, using a geometric method, the biharmonic curves of the three-dimensional Cartan-Vranceanu manifolds.
Dedicated to the memory of Professor Aldo Cossu
Work partially supported by GNSAGA (Italy); the third author was supported by a CNR-NATO fellowship (Italy), and by the Grant
At, 191/2006, CNCSIS (Romania). 相似文献
63.
Cristiane de Melo Cazal Vanessa de Cássia DominguesJaqueline Raquel Batalhão Odair Corrêa BuenoEdson Rodrigues Filho Maria Fátima G. Fernandes da SilvaPaulo Cezar Vieira João Batista Fernandes 《Journal of chromatography. A》2009,1216(19):4307-4312
Xanthyletin, an inhibitor of symbiotic fungus (Leucoagaricus gongylophorus) of leaf-cutting ant (Atta sexdens rubropilosa), as well as suberosin, seselin and xanthoxyletin were isolated from Citrus sinensis grafted on Citrus limonia. A two-phase solvent system composed of hexane/ethanol/acetonitrile/water (10:8:1:1, v/v) was used for the high-speed counter-current chromatographic isolation of xanthyletin with high yield and over 99% purity as determined by liquid and gas chromatography with mass spectrometry detection. Identifications were performed by UV spectra, IR spectra, 1H NMR and 13C NMR. 相似文献
64.
It is common sense to notice that one needs fewer digits to code numbers in ternary than in binary; new names are about log32 times shorter. Is this trade-off a consequence of the special coding scheme? The answer is negative. More generally, we argue that the answer to the question, stated in the title and formulated to the first author by C. Rackhoff, is in fact negative. The conclusion will be achieved by studying the role of the size of the alphabet in constructing instantaneous codes for all natural numbers, and defining random strings and sequences. We show that there is no optimal instantaneous code for all positive integers, and the binary is the worst possible. Codes over a fixed alphabet can be indefinitely improved themselves, but only “slightly”; in contrast, changing the size of the alphabet determines a significant, not linear, improvement. The key relation describing the above phenomenon can be expressed in terms of Chaitin complexity: changing the size of the coding alphabet from q to Q, 2 ≤ q < Q, results in an improvement of the complexity by a factor og log q. As a consequence, a string avoiding consistently a fixed letter is not random. In binary, this corresponds to a trivial situation. In the nonbinary case the distinction is relevant: more than 3.2n ternary strings of length n are not random (many of these strings are binary random). This phenomenon is even sharper for infinite sequences. 相似文献
65.
Mariana Tătucu Petre Rotaru Ileana Rău Cezar Spînu Angela Kriza 《Journal of Thermal Analysis and Calorimetry》2010,100(3):1107-1114
Pyridine derivative complexes are widely employed as biological active materials especially as antibacterial agents. Five transition metal(II) mpk complexes (mpk = methyl 2-pyridyl ketone) were synthesized and investigated using elemental analysis, spectroscopic techniques (IR and UV–Vis–NIR) and conductometric measurements. The general formulae established from experimental data were found to be [M(mpk)2(NO3)2]·xH2O (x = 0 for M = Cd(II), Zn(II), x = 2 for M = Cu(II)) and [M(mpk)2(H2O)2](NO3)2 (M = Co(II), Ni(II)). These compositions were further confirmed by thermal analysis and their thermal stability in dynamic air atmosphere investigated. 相似文献
66.
[reaction: see text] The Heck arylation of acyclic- and cyclic-substituted acrylates using several arenediazonium tetrafluoroborates was investigated. Arylations were carried out under aerobic, ligand-free conditions to provide the corresponding substituted acrylates in moderate to high isolated yields. Heck arylations were usually completed in less than 2 h in refluxing methanol. The aza-endocyclic acrylate derivative 11a was converted into the antidepressant drug (+/-)-paroxetine in a concise new route in good overall yield. 相似文献
67.
Salluzzo M Ghiringhelli G Cezar JC Brookes NB De Luca GM Fracassi F Vaglio R 《Physical review letters》2008,100(5):056810
The mechanism of field-effect doping in the 123 high critical temperature superconductors (HTS) has been investigated by x-ray absorption spectroscopy in the presence of an electric field. We demonstrate that holes are created at the CuO chains of the charge reservoir and that field-effect doping of the CuO(2) planes occurs by charge transfer, from the chains to the planes, of a fraction of the overall induced holes. The electronic properties of the charge reservoir and of the dielectric-HTS interface determine the electric field doping of the CuO(2) planes. 相似文献
68.
M. Opel K. -W. Nielsen S. Bauer S. T. B. Goennenwein J. C. Cezar D. Schmeisser J. Simon W. Mader R. Gross 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(4):437-444
The existence of semiconductors exhibiting long-range ferromagnetic ordering at room temperature still is controversial. One
particularly important issue is the presence of secondary magnetic phases such as clusters, segregations, etc. These are often
tedious to detect, leading to contradictory interpretations. We show that in our cobalt doped ZnO films grown homoepitaxially
on single crystalline ZnO substrates the magnetism unambiguously stems from metallic cobalt nano-inclusions. The magnetic
behavior was investigated by SQUID magnetometry, X-ray magnetic circular dichroism, and AC susceptibility measurements. The
results were correlated to a detailed microstructural analysis based on high resolution X-ray diffraction, transmission electron
microscopy, and electron-spectroscopic imaging. No evidence for carrier mediated ferromagnetic exchange between diluted cobalt
moments was found. In contrast, the combined data provide clear evidence that the observed room temperature ferromagnetic-like
behavior originates from nanometer sized superparamagnetic metallic cobalt precipitates. 相似文献
69.
Januário AH Lourenço MV Domézio LA Pietro RC Castilho MS Tomazela DM da Silva MF Vieira PC Fernandes JB França Sde C 《Chemical & pharmaceutical bulletin》2005,53(7):740-742
Crude extracts of callus and roots of Dipteryx odorata were analyzed by HPLC to detect and quantify isoflavone contents. Based on spectroscopic and X-ray crystallography data the structures of two isoflavones were elucidated as 7-hydroxy-4',6-dimethoxyisoflavone and 3',7-dihydroxy-4',6-dimethoxyisoflavone. The production of dry biomass of 7-hydroxy-4',6-dimethoxyisoflavone in cultured callus was 4.12 mg/g, approximately eleven fold higher than the amount accumulated in roots of D. odorata wild-growing plants. The 7-hydroxy-4',6-dimethoxyisoflavone was effective against glyceraldehyde-3-phosphate dehydrogenase from Trypanosoma cruzi. This is the first report on those bioactive isoflavones accumulated in callus of D. odorata. 相似文献
70.
Jan Kuliga Rodrigo Cezar de Campos Ferreirra Rajan Adhikari Stephen Massicot Dr. Michael Lepper Helen Hölzel Prof. Dr. Norbert Jux Dr. Hubertus Marbach Prof. Dr. Abner de Siervo Prof. Dr. Hans-Peter Steinrück 《Chemphyschem》2021,22(4):396-403
We study the interaction and metalation reaction of a free base 5,10,15,20-terakis(4-cyanophenyl)porphyrin (2HTCNPP) with post-deposited Zn atoms and the targeted reaction product Zn-5,10,15,20-terakis(4-cyanophenyl)porphyrin (ZnTCNPP) on a Ag(111) surface. The investigations are performed with scanning tunneling microscopy at room temperature after Zn deposition and subsequent heating. The goal is to obtain further insights in the metalation reaction and the influence of the cyanogroups on this reaction. The interaction of 2HTCNPP with post-deposited Zn leads to the formation of three different 2D ordered island types that coexist on the surface. All contain a new species with a bright appearance, which increases with the amount of post-deposited Zn. We attribute this to metastable SAT (“sitting atop”) complexes formed by Zn and the macrocycle, that is, an intermediate in the metalation reaction to ZnTCNPP, which occurs upon heating to 500 K. Interestingly, the activation barrier for the successive reaction of the SAT complex to the metalated ZnTCNPP species can also be overcome by a voltage pulse applied to the STM tip. 相似文献