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61.
Eva?A.?Gallardo-GutiérrezEmail author Alfonso?Montes-Rodríguez 《Integral Equations and Operator Theory》2004,50(2):211-216
It is shown that the classical Volterra operator, which is cyclic, is not supercyclic on any of the spaces Lp[0, 1], 1 p < . This solves a question posed by Héctor Salas. This contrasts with the fact that the derivative operator, the left inverse of the Volterra operator, although unbounded, is hypercyclic on Lp[0, 1]. 相似文献
62.
63.
Souček [1, 2] discovered an intriguing connection between the standard twistor correspondence and the biquaternionic projective
line
The biquaternionic projective point,
also has twistor structure corresponding to the collection of α- or β-planes passing through the origin in spacetime. The
duality between α- or β-planes is shown to correspond to the choice of left vs. right scalar action. Moreover, we find that
is homeomorphic to the scheme
相似文献
64.
65.
By means of a local integral formula on a maximal surface, which involves the hyperbolic angle between the unit normal vector
field and a fixed timelike direction, we give a new proof of the parametric Calabi-Bernstein theorem. A suitable modification
of the integral formula gives an independent proof to the non-parametric case of this result. 相似文献
66.
Kovala-Demertzi Dimitra Demertzis Mavroudis Yadav Paras Nath Castiñeiras Alfonso West 《Transition Metal Chemistry》1999,24(6):642-647
The synthesis, as well as spectral and structural characterization, of (2-benzoylpyridine-N(4)-methyl-N(4)-phenylthiosemicarbazonato)chloropalladium(II), [Pd(Bz4MePh)Cl], is described. The unit cell contains two crystallographically independent molecules [Pd(1)(Bz4MePh)Cl], (1), and [Pd(2)(Bz4MePh)Cl], (2), stabilized by intra- and intermolecular hydrogen bonding. The distance between the Pd(1) and Pd(2) centres is 3.5038(11) Å. The spectroscopic techniques used in this study are the following: u.v.-visible, i.r. and 1H n.m.r. The protonation constants, determined spectrophotometrically, of the uncoordinated HBz4MePh are pKa1 = 10.82 ± 0.03 and pKa2 = 4.09 ± 0.02. 相似文献
67.
68.
Giovanni Carlo Alfonso Antonio Turturro Maria Pizzoli Mariastella Scandola Giuseppina Ceccorulli 《Journal of Polymer Science.Polymer Physics》1989,27(6):1195-1208
Thermal measurements were carried out to investigate the macrostructure of as-cast poly(vinylidene fluoride) (PVDF)/poly(vinyl pyrrolidone) (PVP) blends. At high PVP content, above about 70 wt.%, the two components form a homogeneously mixed amorphous phase whose Tg varies with composition. Crystals are formed upon casting mixtures richer in PVDF; these systems exhibit complex thermal behavior that cannot be justified by a simple two-phase model. DSC measurements above room temperature on semicrystalline blends show, in addition to the melting of PVDF crystals at temperatures that decrease on increasing PVP content, a glass transition at about 80°C, independent of composition. Experimental results strongly support the hypothesis that an interphase, composed of essentially undiluted noncrystalline PVDF, is always associated with the lamellar crystals. 相似文献
69.
A manganese(II) complex with N,N′-bis(carboxymethyl)dithiooxamide (H4GLYDTO), [Mn(H2GLYDTO)(H2O)2]n, has been synthesized and characterized by elemental analysis and thermogravimetric analysis, as well as by infrared, electronic and EPR spectroscopy and magnetic susceptibility measurements. The crystal and molecular structure of this complex was determined by single-crystal X-ray structure analysis. The compound shows a 3D porous framework with alternate left- and right-handed helical channels where the manganese(II) ions have an octahedral environment. Variable temperature magnetic measurements reveal the existence of very weak antiferromagnetic interactions through the syn-anti carboxylate bridge, with an exchange parameter of J/k = −0.12 K. 相似文献
70.
Isolda C. Mendes Fernanda B. Costa Geraldo M. de Lima José D. Ardisson Isabel Garcia-Santos Alfonso Castiñeiras Heloisa Beraldo 《Polyhedron》2009,28(6):1179-1185
Reaction of tin tetrachloride with 2-pyridineformamide thiosemicarbazone (H2Am4DH) and its N(4)-methyl (H2Am4Me), N(4)-ethyl (H2Am4Et) and N(4)-phenyl (H2Am4Ph) derivatives gave [Sn(2Am4DH)Cl3] (1), [Sn(2Am4Me)Cl3] (2), [Sn(2Am4Et)Cl3] (3) and [Sn(2Am4Ph)Cl3] (4) as products, in which an anionic thiosemicarbazone coordinates to the metal centre along with three chloride ions. The crystal structures of 1 and 2 were determined. The thiosemicarbazones were moderately active against Candida albicans and Pseudomonas aeruginosa. Upon coordination to tin(IV) the antimicrobial activity of the thiosemicarbazones increases. The studied compounds proved to be toxic to Artemia salina, suggesting that they could present cytotoxic activity against solid tumors. 相似文献