Interrelations between Adsorption Energies and Local Isotherms, Local Monolayer Capacities, and Energy Distribution Functions, as Determined for Heterogeneous Surfaces by Inverse Gas Chromatography

Physicochemical parameters for adsorption of gases at the submonolayer regions of heterogeneous solid surfaces are measured experimentally as a function of time, and then interrelated as local isotherms θ against adsorption energy varepsilon, fractional changes of adsorption sites f(varepsilon)/c*(max) against varepsilon, θ against f(varepsilon)/c*(max), and distribution functions θ f(varepsilon)/c*(max) over adsorption energy values varepsilon, without using at all the well-known integral equation Theta(p, T)=integral(infinity)(0)θ(p, T, varepsilon)f(varepsilon)dvarepsilon and assumptions concerning the pair f(varepsilon) and θ(p, T, varepsilon). The method uses only chromatographic experimental data obtained by the inverse gas chromatography technique known as reversed-flow gas chromatography. It has been applied to the adsorption of cis-2-butene and trans-2-butene onto particles of Penteli marble at temperatures of 302, 314, 323, and 333 K. The results obtained are comparable with those calculated on the basis of the well-known integral equation. Copyright 2001 Academic Press.     

Thermomechanical Properties of Carbon Nanocomposites PEGDA Photopolymers

In this work, UV-curable resin poly (ethylene glycol) diacrylate (PEGDA) was reinforced with three different types of nanofillers: pristine graphene (G), multiwalled carbon nanotubes (MWNTs), and a hybrid of MWNTs and graphene 70/30 in mass ratio (Hyb). PEGDA was mixed homogenously with the nanofiller oligomer by shear mixing and then photopolymerized, affording thin, stable films. The thermomechanical properties of the afforded nanocomposites indicated the superior reinforcing ability of pristine graphene compared with MWNTs and an intermediate behavior of the hybrid.     

Experimental and theoretical study of the antisymmetric magnetic behavior of copper inverse-9-metallacrown-3 compounds

Use of PhPyCNO (-)/X (-) "blends" (PhPyCNOH = phenyl 2-pyridyl ketoxime; X (-) = OH (-), alkanoato, ClO 4 (-)) in copper chemistry yielded trinuclear clusters that have been characterized as inverse-9-metallacrown-3 compounds and accommodate one or two guest ligands. The magnetic behavior showed a large antiferromagnetic interaction and a discrepancy between the low-temperature magnetic behavior observed experimentally and that predicted from a magnetic model. The discrepancy between the Brillouin curve and the experimental result provides clear evidence of the influence of the antisymmetric interaction. Introducing the antisymmetric terms derived from the fit of the susceptibility data into the magnetization formula caused the simulated curve to become nearly superimposable on the experimental one. The EPR data indicated that the compound [Cu 3(PhPyCNO) 3(mu 3-OH)(2,4,5-T) 2] ( 1), where 2,4,5-T is 2,4,5-trichlorophenoxyacetate, has isosceles or lower magnetic symmetry (delta not equal 0), that antisymmetric exchange is important ( G not equal 0), and that Delta E > hnu. The structures of the complexes 1 and [Cu 3(PhPyCNO) 3(mu 3-OH)(H 2O)(ClO 4) 2] ( 2) were determined using single-crystal X-ray crystallography. Theoretical calculations based on density functional theory were performed using the full crystal structures of 1, 2, [Cu 3(PhPyCNO) 3(OH)(CH 3OH) 2(ClO 4) 2] ( 3), and [Cu 3(PhPyCNO) 3(mu 3-OMe)(Cl)(ClO 4)] ( 4). The geometries of the model compounds [Cu 3(kappa (3) N, N, O-HNCHCHNO) 3(mu 3-OH)(mu 2-HCOO)(HCOO)] ( 5), [Cu 3(kappa (3) N, N, O-HNCHCHNO) 3(mu 2-HCOO)(HCOO)] (+) ( 6), [Cu 3(kappa (3) N, N, O-HNCHCHNO) 3(mu 3-O)] (+) ( 7), and [Cu 3(kappa (3) N, N, O-HNCHCHNO) 3] (3+) ( 8) were optimized at the same level of theory for both the doublet and quartet states, and vibrational analysis indicated that the resulting equilibrium geometries corresponded to minima on the potential energy surfaces. Both e g and t 2g magnetic orbitals seem to contribute to the magnetic exchange coupling. The latter contribution, although less important, might be due to overlap of the t 2g orbitals with the p-type orbitals of the central triply bridging oxide ligand, thereby affecting its displacement from the Cu 3 plane and contributing to the antiferromagnetic coupling. The crucial role of the triply bridging oxide (mu 3-O) ligand on the antiferromagnetic exchange coupling between the three Cu(II) magnetic centers is further evidenced by the excellent linear correlation of the coupling constant J with the distance of the mu 3-O ligand from the centroid of the Cu 3 triangle.     

Structural features of mono- and tri-nuclear Zn(II) complexes with a non-steroidal anti-inflammatory drug as ligand

The interaction of Zn(II) with the non-steroidal anti-inflammatory drug tolfenamic acid leads to the formation of the structurally characterized trinuclear [Zn(3)(tolfenamato)(6)(CH(3)OH)(2)] complex. In the presence of the N,N'-donor heterocyclic ligands 1,10-phenanthroline and 2,2'-bipyridine at a range of ratios, the mononuclear Zn complexes of the general formulae [Zn(tolfenamato)(N,N'-donor)Cl] and [Zn(tolfenamato)(2)(N,N'-donor)] have been isolated and structurally characterized by X-ray crystallography. The deprotonated tolfenamato ligands are coordinated to the Zn(II) ion through carboxylato oxygen atoms. Tolfenamic acid and its complexes exhibit good binding propensity to human or bovine serum albumin protein having relatively high binding constant values.     

Special issue on global flow instability and control

This special issue is the second on the topic of “Global Flow Instability and Control,” following the first in 2011. As with the previous special issue, the participants of the last two symposia on Global Flow Instability and Control, held in Crete, Greece, were invited to submit publications. These papers were peer reviewed according to the standards of the journal, and this issue represents a snapshot of the progress since 2011. In this preface, a sampling of important developments in the field since the first issue is discussed. A synopsis of the papers in this issue is given in that context.     

Three dimensional combined fracture–plastic material model for concrete

This paper describes a combined fracture–plastic model for concrete. Tension is handled by a fracture model, based on the classical orthotropic smeared crack formulation and the crack band approach. It employs the Rankine failure criterion, exponential softening, and it can be used as a rotated or a fixed crack model. The plasticity model for concrete in compression is based on the Menétrey–Willam failure surface, the plastic volumetric strain as a hardening/softening parameter and a non-associated flow rule based on a nonlinear plastic potential function. Both models use a return-mapping algorithm for the integration of constitutive equations. Special attention is given to the development of an algorithm for the combination of the two models. The suggested combination algorithm is based on a recursive substitution, and it allows for the two models to be developed and formulated separately. The algorithm can handle cases when failure surfaces of both models are active, but also when physical changes such as crack closure occur. The model can be used to simulate concrete cracking, crushing under high confinement and crack closure due to crushing in other material directions. The model is integrated in a general finite element package ATENA and its performance is evaluated by comparisons with various experimental results from the literature.