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Riadh Marzouki Abderrahmen Guesmi Ahmed Driss 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(10):i95-i98
The title compound, tetrasodium cobalt aluminium hexaarsenate, Na4Co7−xAl2/3x(AsO4)6 (x = 1.37), is isostructural with K4Ni7(AsO4)6; however, in its crystal structure, some of the Co2+ ions are substituted by Al3+ in a fully occupied octahedral site (site symmetry 2/m) and a partially occupied tetrahedral site (site symmetry 2). A third octahedral site is fully occupied by Co2+ ions only. One of the two independent tetrahedral As atoms and two of its attached O atoms reside on a mirror plane, as do two of the three independent Na+ cations, all of which are present at half‐occupancy. The proposed structural model based on a careful investigation of the crystal data is supported by charge‐distribution (CHARDI) analysis and bond‐valence‐sum (BVS) calculations. The correlation between the X‐ray refinement and the validation results is discussed. 相似文献
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This research aims to highlight and examine an example of ecological complexity. By taking into account the interference between predator and prey, we introduce an ecological system with a general functional response. This model is perturbed by a novel class of fluctuations in the polynomial form. Analytically, we present an alternative method to obtain the acute threshold between stationarity and predator disappearance. Our analysis enriches and improves the work of Zhou et al. (2021) by unifying the criteria of said asymptotic characteristics. Numerically, we audit the accuracy of our threshold in three particular situations: linear, quadratic and cubic perturbations. We establish that the increasing order of disturbance has a passive influence on the extinction time of predators. This finding highlights that complex noise sources have a positive role in the transient dynamics of ecological systems. 相似文献
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Let R be a ring,X a class of R-modules and n ≥ 1 an integer.We intro-duce the concepts of Gorenstein n-X-injective and n-X-flat modules via special finitely presented modules.Besides,we obtain some equivalent properties of these modules on n-X-coherent rings.Then we investigate the relations among Gorenstein n-X-injective,n-X-flat,injective and fiat modules on X-FC-rings (i.e.,self n-X-injective and n-X-coherent rings).Several known results are generalized to this new context. 相似文献
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Salah Kouass Abderrahmen Guesmi Ahmed Driss 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(1):i4-i6
The title compound, namely lithium cobalt(II/III) bis(diphosphate), Li4.03Co1.97(P2O7)2, is a new mixed‐valent lithium/cobalt(II/III) phosphate. Three metal sites out of seven are occupied simultaneously by Li+ and CoII/III ions. This disorder was established both from an analysis of the atomic displacement ellipsoids and Li/Co—O bond distances, and by means of a charge‐distribution (CHARDI) model, which provides satisfactory agreement on the computed charges (Q) for all the cations. 相似文献
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Driss Drissi 《Complex Analysis and Operator Theory》2010,4(4):813-819
Let {x n } be a sequence of complex numbers and let \({\Delta^nx_j = \sum\nolimits_{k=0}^{n} (-1)^k\break\left(\begin{array}{l}n\\ k\\\end{array} \right)x_{n-k+j}}\) . In this paper, we will show that if \({ |x_n| = O(n^k)}\) , as n → ∞ for some positive integer k, and \({n|\Delta^n x_j|^{\frac{1}{n}} \to 0}\) as n→ ∞, then \({\Delta^{k+1} x_j = 0}\) . More importantly, applications to the orbits of operators and invariant subspace problem are also given; this helps to improve former results obtained by Gelfand–Hille, Mbekhta–Zemánek and others. 相似文献