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排序方式: 共有137条查询结果,搜索用时 31 毫秒
41.
Dario A. Bini Guy Latouche Beatrice Meini 《Linear algebra and its applications》2002,340(1-3):225-244
The matrix equation ∑i=0nAiXi=0, where the Ai's are m×m matrices, is encountered in the numerical solution of Markov chains which model queueing problems. We provide here a unifying framework in terms of Möbius' mapping to relate different resolution algorithms having a quadratic convergence. This allows us to compare algorithms like logarithmic reduction (LR) and cyclic reduction (CR), which extend Graeffe's iteration to matrix polynomials, and the invariant subspace (IS) approach, which extends Cardinal's algorithm. We devise new iterative techniques having quadratic convergence and present numerical experiments. 相似文献
42.
It is shown that photoinduced reactions are observed at room temperature and pressure of few tenths of gigapascal in clathrate hydrates of CO and of model hydrocarbons under mild irradiation at 350 nm with power in the 50-610 mW range. The reactions are triggered by highly reactive OH radicals produced by two-photon excitation of the lowest electronic excited state of water having dissociative character. The formation of CO(2) is observed in all the reactions involving carbonaceous clathrate hydrates, and direct or indirect evidence for the formation of molecular hydrogen is obtained. The CO(2) produced in the reactions can be sequestered as a clathrate hydrate whose stability range seems to extend to room temperature at pressures of 0.5-0.6 GPa. Although the N(2) hydrate is stable up to 0.9 GPa under irradiation, a partial cleavage of the N-N triple bond is produced once the hydrate decomposes at 0.1 GPa. 相似文献
43.
Rafael A. Bini Rodrigo Fernando C. MarquesFrancisco J. Santos Juliano A. ChakerMiguel Jafelicci Jr. 《Journal of magnetism and magnetic materials》2012,324(4):534-539
Superparamagnetic iron oxide (SPIO) nanoparticles show great promise for many biotechnological applications. This paper addresses the synthesis and characterization of SPIO nanoparticles grafted with three different alkoxysilanes: 3-aminopropyl-triethoxysilane (APTES), 3-aminopropyl-ethyl-diethoxysilane (APDES) and 3-aminopropyl-diethy-ethoxysilane (APES). SPIO nanoparticles with an average particle diameter of 10 nm were prepared by chemical sonoprecipitation. As confirmed by Fourier transform infrared (FTIR) spectroscopy, silylation of these nanoparticles occurs through a two-step process. Decreasing the number of alkoxide groups reduced the concentration of free amino groups on the SPIO surface ([SPIO-NH2]—APTES>APDES>APES). This phenomenon results from steric contributions and the formation of H-bonded amines provided by the ethyl groups present in the APDES and APES molecules. A simulation of SPIO nanoparticles in a saline physiologic solution shows that the ethyl groups impart larger steric stability onto the ferrofluids, which reduces aggregation. The magnetization (M) versus magnetic field (H) curves show that the synthesized iron oxide nanoparticles display superparamagnetic behavior. The zero-field cooling (ZFC) and field cooling (FC) curves show that the changes in the blocking temperature depend on the alkoxysilane-functionalized particle surface. 相似文献
44.
Donato Bini Christian Cherubini Simonetta Filippi Andrea Geralico 《General Relativity and Gravitation》2009,41(12):2781-2795
An exact solution of Einstein’s equations representing the static gravitational field of a quasi-spherical source endowed
with both mass and mass quadrupole moment is considered. It belongs to the Weyl class of solutions and reduces to the Schwarzschild
solution when the quadrupole moment vanishes. The geometric properties of timelike circular orbits (including geodesics) in
this spacetime are investigated. Moreover, a comparison between geodesic motion in the spacetime of a quasi-spherical source
and non-geodesic motion of an extended body also endowed with both mass and mass quadrupole moment as described by Dixon’s
model in the gravitational field of a Schwarzschild black hole is discussed. Certain “reciprocity relations” between the source
and the particle parameters are obtained, providing a further argument in favor of the acceptability of Dixon’s model for
extended bodies in general relativity. 相似文献
45.
A. A. Stefanini M. Bini G. Casini P. R. Maurenzig A. Olmi G. Pasquali S. Piantelli G. Poggi N. Taccetti 《Acta Physica Hungarica A》2002,16(1-4):379-386
New experimental results on pre-equilibrium effects and neck emission at Fermi energies are presented. Coulomb trajectory calculations have been performed to explain the observed IMF velocity distributions. 相似文献
46.
The phase diagram of propene has been investigated at high pressure by using the diamond anvil cell technique and Fourier transform infrared spectroscopy. The pressure conditions necessary to induce a spontaneous reaction of the sample have been found at different temperatures, allowing the stability boundary of propene to be drawn. The reaction is diffusion controlled and seems to occur only in the fluid phase, implying a slope inversion of the stability boundary at about 250 K. The product of the reaction is a mixture of linear oligomers independently of the P-T conditions. The activation volume and energy of the process have been obtained from the kinetic data. Also the activation of the reaction by laser absorption has been carefully studied. A high proton mobility has been identified as the likely reason that limits the lengthening of the chain up to six to eight monomeric units preventing the polymer formation. 相似文献
47.
Metal complexes of poly(acrylic acid): synthesis, characterization and thermogravimetric studies 总被引:1,自引:0,他引:1
Thermogravimetric studies of the sodium salt of poly(acrylic acid), its modified sodium salt and its various metal complexes were made. The thermal stabilities of the various systems decreased in the order: poly(acrylic acid) > Ni(II) > Co(II) > Zn(II) > Fe(III) > Cu(II) > polymeric sodium salt. The higher thermal stabilities of the polymer-metal complexes result from the development of stable ring structures in the polymer matrix upon coordination with metal ions. The metal-ion complexation of carboxylate ligands of linear poly(acrylic acid), optimization of the complexation conditions and infra-red and ultraviolet-visible spectrometric characterizations are also illustrated. 相似文献
48.
Modesti A Bini L Carraresi L Magherini F Liberatori S Pallini V Manao G Pinna LA Raugei G Ramponi G 《Electrophoresis》2001,22(3):576-585
Small tyrosine phoshatase 1 (Stp1) is a Schizosaccharomyces pombe low-molecular-mass phosphotyrosine-phosphatase 50% identical to Saccharomyces cerevisiae Ltp1. In order to investigate the role of Stp1 in yeast, a mutant was generated having the characteristic of a dominant negative molecule. Changes in protein tyrosine phosphorylation in S. cerevisiae proteome in response to Stp1 or its dominant negative mutant expression were analyzed by high-resolution two-dimensional (2-D) electrophoresis. The most remarkable result is the modification by phosphorylation on tyrosine of several proteins involved in carbohydrate metabolism. Twelve proteins were identified on the basis of their positions in the anti-phosphotyrosine immunoblot of the 2-D electrophoresis. Ten of these present tyrosyl residues that are within the consensus sequence for protein kinase CK2 (casein kinase-2). These data open the possibility for the identification of Stp1 substrates in yeast and provide hints about the nature of tyrosine phosphorylating agents in yeast and in other organisms where bona fide tyrosine kinases are lacking. 相似文献
49.
Dextran‐Coated Antiferromagnetic MnO Nanoparticles for a T1‐MRI Contrast Agent with High Colloidal Stability
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Herbert R. Neves Rafael A. Bini Jeam H. O. Barbosa Carlos E. G. Salmon Laudemir C. Varanda 《Particle & Particle Systems Characterization》2016,33(3):167-176
A simple approach to synthesize carboxymethyl dextran‐coated MnO nanoparticles (CMDex‐MnONPs) with high colloidal stability in physiological saline solutions is described here for potential applications as a magnetic resonance imaging (MRI) T1 contrast agent. The thermal decomposition methodology is used to produce uniform MnONPs with an average size of around 20 nm, and its hydrophobic surface is modified with CMDex molecules, conferring hydrophilic properties. After CMDex coating, the nanoparticle presents high colloidal stability in concentrations ranging from 10 to 50 μg mL?1, average hydrodynamic size (Z‐average) of 130 nm, polydispersity degree of ≈12%, and negative surface charge in both simulated body fluid solutions and pure water with zeta‐potential of –20 and –40 mV, respectively. The CMDex‐MnONPs with 20 nm show antiferromagnetic behavior at room temperature, and the magnetic properties are found to be strongly dependent of the nanoparticle size, increasing the contribution of the ferromagnetic Mn3O4 phase with decreasing size for nanoparticles about 3 nm. Cytotoxicity evaluation in cancerous and noncancerous cells in the range of 5.0–50.0 μg mL?1 shows low toxicity for cancerous cells and lack of the same for healthy cells lines. Related to the magnetic properties, CMDex‐MnONP presents significant r1 relaxivity and low r2/r1 relaxivity ratio. The results suggest that these nanoparticles display characteristics for potential applications as an MRI T1 contrast agent. 相似文献
50.
de Boer JW Browne WR Harutyunyan SR Bini L Tiemersma-Wegman TD Alsters PL Hage R Feringa BL 《Chemical communications (Cambridge, England)》2008,(32):3747-3749
High turnover enantioselective alkene cis-dihydroxylation is achieved with H(2)O(2) catalysed by manganese based complexes containing chiral carboxylato ligands. 相似文献