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221.
Nonlinear Dynamics - To study the collective behavior and the regulation mechanism of memristor, the Hindmarsh–Rose neuron cells are selected as the units to construct a coupled system by... 相似文献
222.
Brett W. Boote Himashi P. Andaraarachchi Bryan A. Rosales Rafael Blome-Fernández Feng Zhu Malinda D. Reichert Kalyan Santra Jingzhe Li Jacob W. Petrich Javier Vela Emily A. Smith 《Chemphyschem》2019,20(20):2647-2656
Lead halide perovskites possess unique characteristics that are well-suited for optoelectronic and energy capture devices, however, concerns about their long-term stability remain. Limited stability is often linked to the methylammonium cation, and all-inorganic CsPbX3 (X=Cl, Br, I) perovskite nanocrystals have been reported with improved stability. In this work, the photostability and thermal stability properties of CsPbX3 (X=Cl, Br, I) nanocrystals were investigated by means of electron microscopy, X-ray diffraction, thermogravimetric analysis coupled with FTIR (TGA-FTIR), ensemble and single particle spectral characterization. CsPbBr3 was found to be stable under 1-sun illumination for 16 h in ambient conditions, although single crystal luminescence analysis after illumination using a solar simulator indicates that the luminescence states are changing over time. CsPbBr3 was also stable to heating to 250 °C. Large CsPbI3 crystals (34±5 nm) were shown to be the least stable composition under the same conditions as both XRD reflections and Raman bands diminish under irradiation; and with heating the γ (black) phase reverts to the non-luminescent δ phase. Smaller CsPbI3 nanocrystals (14±2 nm) purified by a different washing strategy exhibited improved photostability with no evidence of crystal growth but were still thermally unstable. Both CsPbCl3 and CsPbBr3 show crystal growth under irradiation or heat, likely with a preferential orientation based on XRD patterns. TGA-FTIR revealed nanocrystal mass loss was only from liberation and subsequent degradation of surface ligands. Encapsulation or other protective strategies should be employed for long-term stability of these materials under conditions of high irradiance or temperature. 相似文献
223.
AbstractIn this paper we introduce the notion of extension of a numerical semigroup. We provide a characterization of the numerical semigroups whose extensions are all arithmetic and we give an algorithm for the computation of the whole set of arithmetic extension of a given numerical semigroup. As by-product, new explicit formulas for the Frobenius number and the genus of proportionally modular semigroups are obtained. 相似文献
224.
Whiteoak CJ Torres Martin de Rosales R White AJ Britovsek GJ 《Inorganic chemistry》2010,49(23):11106-11117
Tetradentate bis(aminophenolate) ligands H(2)salan(X) and H(2)bapen(X) (where X refers to the para-phenolate substituent = H, Me, F, Cl) react with [Fe{N(SiMe(3))(2)}(2)] to form iron(II) complexes, which in the presence of suitable donor ligands L (L = pyridine or THF) can be isolated as the complexes [Fe(salan(X))(L)(2)] and [Fe(bapen(X))(L)(2)]. In the absence of donor ligands, either mononuclear complexes, for example, [Fe(salan(tBu,tBu))], or dinuclear complexes of the type [Fe(salan(X))](2) are obtained. The dynamic coordination behavior in solution of the complexes [Fe(salan(F))(L)(2)] and [Fe(bapen(F))(L)(2)] has been investigated by VT (1)H and (19)F NMR spectroscopy, which has revealed equilibria between isomers with different ligand coordination topologies cis-α, cis-β and trans. Exposure of the iron(II) salan(X) complexes to O(2) results in the formation of oxo-bridged iron(III) complexes of the type [{Fe(salan(X))}(2)(μ-O)] or [{Fe(salan(X))(L)}(2)(μ-O)]. The lack of catalytic activity of the iron(II) salan and bapen complexes in the oxidation of cyclohexane with H(2)O(2) as the oxidant is attributed to the rapid formation of stable and catalytically inactive oxo-bridged iron(III) complexes. 相似文献
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Merlín Rosales Otto Soto Beatriz González Inés Pacheco Pablo J. Baricelli 《Transition Metal Chemistry》2018,43(5):451-461
Limonene hydroformylation was studied in the presence of Rh-based catalytic systems, which were prepared in situ by addition of three equivalents of PPh3, one of 1,2-bis(diphenylphosphino)ethane (dppe), or one of 1,1,1-tris(diphenylphosphino)ethane (triphos) to Rh(CO)2(acac) (1). These systems were efficient precatalysts for the target reaction, generating limonenal regio-specifically under mild reaction conditions (80 °C and 20 atm of syngas). The found activity order was: (1)/3 PPh3?>?(1)/triphos?>?(1)/dppe. The active catalytic species are proposed to be square planar hydrido-carbonyl complexes containing two phosphorus atoms coordinated at the rhodium centre. A kinetic study of this reaction catalysed by (1)/3 PPh3, the most active catalytic system, allowed us to propose that the mechanism of hydroformylation of limonene is similar to those reported for other olefins using RhH(CO)(PPh3)3 or Rh systems containing either dppe or triphos as precatalysts. 相似文献
229.
We extend the concept of presentation of finitely generated commutative monoids to ideals of finitely generated commutative monoids and give algorithms to obtain information about an ideal from a given presentation. 相似文献
230.