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11.
The double-layered LaSr2Mn2O7 manganite was synthesized by the sol–gel process. Two samples with the average grain size from ~150 nm to ~1 μm were prepared by controlling the sintering temperature. Both samples had a tetragonal structure, with a small fraction of impurity phase in the S-1250 sample. In order to investigate the probable influence of grain size on the conduction mechanism, resistivity of the samples was measured as a function of temperature, and the data obtained was analyzed by different conduction mechanisms. It was found that with increase in the grain size, resistivity decreased at all temperature ranges. The results show that the adiabatic small polaron hopping (SPH) model is probably responsible for conduction at high temperature range, and that the 3D variable range hopping (VRH) model shows a better correlation with the experimental data for low temperature range. These analyses indicate the influence of grain size on the parameters obtained from fitting the data by both models. 相似文献
12.
Density functional molecular dynamical calculations have been carried out to explore the effect of silicon impurities on thermodynamic properties of Ga(30). We have obtained 500 distinct low energy equilibrium geometries of Ga(27)Si(3) in order to obtain reliable ground state geometry. The specific heat has been calculated using multiple histogram techniques and compared with that of Ga(30). We demonstrate that silicon impurities have a dramatic effect on the thermodynamic properties of the host cluster. In contrast to Ga(30), the specific heat of Ga(27)Si(3) shows a clear melting peak at ≈500 K, changing the character of Ga(30) from a nonmelter to a melter. 相似文献
13.
14.
Farrokh Gharib Saeid Taghvaei Sara Ghazi 《Russian Journal of Inorganic Chemistry》2007,52(12):1915-1917
The synthesis and complexing abilities of 26,28-bis-benzyloxy-25,27-dihydroxy-5,11,17,23-tetra-tertbutyl-calix[4]arene towards
alkali earth metal ions Mg2+, Ca2+, Sr2+, and Ba2+ in a methanol-chloroform mixture have been evaluated at 25°C, using UV-Vis spectrophotometric techniques. The results showed
that the ligand is capable to complex all alkali earth cations by 1:1 metal to ligand ratios. The selectivity presented considering
the calculated stability constants are in the order Mg2+ > Ca2+ > Sr2+ > Ba2+ towards the ligand. 相似文献
15.
Ghazi Kassab Dominique Petit Jean-Pierre Korb Tahar Tajouri Pierre Levitz 《Comptes Rendus Chimie》2010,13(4):394-398
Reversed micelles and water in oil micro-emulsions can be used to solubilize biopolymers and genetic materials allowing analyzing their properties in a confined geometry. Nuclear Magnetic Resonance Dispersion (NMRD) provides a powerful and a noninvasive experimental technique to probe the long-term dynamics of these confined systems. However, the first step is to analyze and understand the slow dynamics of water inside these micro-reactors without any guest molecule. This is the aim of this presentation. Experimental results have been obtained for deuteron 2H NMRD of water confined in reverse micelles of bis (2-ethylhexyl) sodium sulfosuccinate (AOT) dispersed in isooctane C8H18. The water content is expressed as the molar ratio W0 = [Water]/[AOT]. The radius of the spherical reversed micelles, Rm, increases almost linearly with W0. In our case, W0 is chosen in the range 20 ≤ W0 ≤ 50 (35 ≤ Rm ≤ 80 Å). The frequency dependence for the spin-lattice relaxation rate R1(ω) exhibits two regimes, for all W0 values: a plateau at low frequency, proportional to 1/Rm, followed by the beginning of an algebraic decay. These experimental observations are discussed and compared to a numerical simulation of the intermittent Brownian diffusion of a water molecule inside a rotating reverse micelle. The possibility to probe some properties of the confinement, such as the localisation time on the sulfonated palisade and/or the water self-diffusion inside the water pool is emphasised. 相似文献
16.
Mathematical models have been developed to optimize three configurations for membrane gas separation modules. The three systems include the single stage, the two stage, and the continuous membrane column (CMC). Analysis of the three systems is carried out for the case of enriching a binary mixture of methane and carbon dioxide, where the reject stream is the desired product. The cost optimization function includes the capital cost for compressors and membranes as well as the energy operating cost. The cost function is solved subject to a set of equality and inequality constraints. The equality constraints include the module balance equations and the permeation fluxes across the membrane. The inequality equations include constraints on mole fractions in permeate and reject streams, operating pressure, membrane area, and the amount of methane recovered in reject stream. Model equations for the three systems are solved using GINO, a program for nonlinear optimization. A quasi-Newton search method is selected and found quite efficient for solution of the equations. Over the range of parameters considered in the analysis, results show that the two stage configuration has a lower production cost than the other two systems. In addition, the operating cost for the CMC and the single stage systems are found to be comparable. Irrespective of this, the optimum amount of methane recovered is the highest for the CMC system. Although the optimum operating costs for the CMC and the single stage systems are higher than the two stage system, comparison should consider other factors including higher methane recoveries generated by the CMC system and the simplicity of design and operation for the single stage system. 相似文献
17.
Colacio E Ghazi M Stoeckli-Evans H Lloret F Moreno JM Pérez C 《Inorganic chemistry》2001,40(19):4876-4883
Reactions between [M(N(4)-macrocycle)](2+) (M = Zn(II) and Ni(II); macrocycle ligands are either CTH = d,l-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane or cyclam = 1,4, 8, 11-tetrazaazaciclotetradecane) and [M(CN)(6)](3-) (M = Fe(III) and Mn(III)) give rise to cyano-bridged assemblies with 1D linear chain and 2D honeycomblike structures. The magnetic measurements on the 1D linear chain complex [Fe(cyclam)][Fe(CN)(6)].6H(2)O 1 points out its metamagnetic behavior, where the ferromagnetic interaction operates within the chain and the antiferromagnetic one between chains. The Neel temperature, T(N), is 5.5 K and the critical field at 2 K is 1 T. The unexpected ferromagnetic intrachain interaction can be rationalized on the basis of the axially elongated octahedral geometry of the low spin Fe(III) ion of the [Fe(cyclam)](3+) unit. The isostructural substitution of [Fe(CN)(6)](3-) by [Mn(CN)(6)](3-) in the previously reported complex [Ni(cyclam)](3)[Fe(CN)(6)](2).12H(2)O 2 leads to [Ni(cyclam)](3)[Mn(CN)(6)](2).16 H(2)O 3, which exhibits a corrugated 2D honeycomblike structure and a metamagnetic behavior with T(N) = 16 K and a critical field of 1 T. In the ferromagnetic phase (H > 1 T) this compound shows a very important coercitive field of 2900 G at 2 K. Compound [Ni(CTH)](3)[Fe(CN)(6)](2).13H(2)O 4, C(60)H(116)Fe(2)N(24)Ni(3)O(13), monoclinic, A 2/n, a = 20.462(7), b = 16.292(4), c = 27.262(7) A, beta = 101.29(4) degrees, Z = 4, also has a corrugated 2D honeycomblike structure and a ferromagnetic intralayer interaction, but, in contrast to 2 and 3, does not exhibit any magnetic ordering. This fact is likely due to the increase of the interlayer separation in this compound. ([Zn(cyclam)Fe(CN)(6)Zn(cyclam)] [Zn(cyclam)Fe(CN)(6)].22H(2)O.EtOH) 5, C(44)H(122)Fe(2)N(24)O(23)Zn(3), monoclinic, A 2/n, a = 14.5474(11), b = 37.056(2), c = 14.7173(13) A, beta = 93.94(1) degrees, Z = 4, presents an unique structure made of anionic linear chains containing alternating [Zn(cyclam)](2+) and [Fe(CN)(6)](3)(-) units and cationic trinuclear units [Zn(cyclam)Fe(CN)(6)Zn(cyclam)](+). Their magnetic properties agree well with those expected for two [Fe(CN)(6)](3-) units with spin-orbit coupling effect of the low spin iron(III) ions. 相似文献
18.
Yang W Jones LM Isley L Ye Y Lee HW Wilkins A Liu ZR Hellinga HW Malchow R Ghazi M Yang JJ 《Journal of the American Chemical Society》2003,125(20):6165-6171
Calcium ions play key roles as structural components in biomineralization and as a second messenger in signaling pathways. We have introduced a de novo designed calcium-binding site into the framework of a non-calcium-binding protein, domain 1 of CD2. The resulting protein selectively binds calcium over magnesium with calcium-binding affinity comparable to that of natural extracellular calcium-binding proteins (K(d) of 50 microM). This experiment is the first successful metalloprotein design that has a high coordination number (seven) metal-binding site constructed into a beta-sheet protein. Our results demonstrate the feasibility of designing a single calcium-binding site into a host protein, taking into account only local properties of a calcium-binding site obtained by a survey of natural calcium-binding proteins and chelators. The resulting site exhibits strong metal selectivity, suggesting that it should now be feasible to understand and manipulate signaling processes by designing novel calcium-modulated proteins with specifically desired functions and to affect their stability. 相似文献
19.
Chady Ghnatios Ghazi Asmar Elie Chakar Charbel Bou Mosleh 《Comptes Rendus Mecanique》2019,347(2):101-113
Automation is conquering new fields on a daily basis. Aiming for faster and more reliable products, industrials as well as researchers are oriented into automation. Non-destructive testing as well as defect quantification is not an exception. In fact, decisions with minimum allowable error are sought in real-time when facing any potential defect. In this work, we suggest a comprehensive method based on model order reduction techniques to judge if a structure shall be salvaged. The real-time decision is based on multidimensional parametric simulation, performed offline, using the Proper Generalized Decomposition (PGD). The PGD is a model order reduction technique that allows circumventing the curse of dimensionality by using domain decomposition. Therefore, the 6D simulation illustrated in this paper is performed within a few minutes on a standard laptop. Later on, a stress concentration manifold is built and used online for decision-making. The manifold is validated on a few selected solutions solved analytically using an analytical procedure. The aforementioned procedure is developed, in this paper, to calculate the tangential stress around circular holes of different sizes, in an infinite isotropic plate containing any number of holes and subjected to in-plane pressure loading at the tip of the infinite plate. The procedure is based on determining two Muskhelishvili complex potentials in terms of complex Fourier series, and applying the Schwartz alternating method repeatedly until the boundary conditions on the contour of every hole are satisfied. 相似文献
20.
P. D.?Spencer M. E.?Ghazi S. B.?Wilkins P. D.?HattonEmail author S. D.?Brown D.?Prabhakaran A. T.?Boothroyd 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,46(1):27-32
We present high resolution X-ray measurements
characterising the charge stripe order state in the
La2-xSrxNiO4 system with x = 0.20, 0.225 and 0.25. We
find that in the x = 0.20, 0.225 and 0.25 systems the charge
stripe order exists in a charge stripe glass characterised by
weak, poorly correlated incommensurate charge stripes in contrast
to the strong well correlated charge stripes in the commensurate
x = 1/3 system. No stabilisation of the charge order was
observed at the next possible commensurate value of ε= 0.25. A comparison with high energy X-ray measurements suggested
that the charge order may exist in a charge stripe glass in the
bulk in the doping region x = 0.20 - 0.33. Finally at low
temperature there was an initial increase in the intensity and
correlation not observed with neutron measurements and it appears
to be an effect that X-rays are sensitive to but neutrons are not. 相似文献