Structural Diversity of Copper(II) Complexes with 9-Deazahypoxanthine and Their in Vitro SOD-Like Activity

Two structurally different copper(II) complexes of the compositions [{Cu(9dhx)(H₂O)₃}₂(µ-SO₄)₂] (1) and [Cu(9dhx)₂(H₂O)₂(NO₃)₂]·H₂O (2), involving 9-deazahypoxanthine (9dhx; 6-oxo-9-deazapurine; 9-deazahypoxanthine), have been prepared and characterized by elemental analysis, infrared and electronic spectroscopy, electrospray ionisation (ESI) mass spectrometry, thermogravimetric (TG) and differential thermal (DTA) analyses, and cyclic voltammetry. The X-ray structures of complexes 1 and [Cu(9dhx)₂(H₂O)₂(NO₃)₂] (2a) revealed the distorted octahedral geometry in the vicinity of the copper(II) atoms, with the NO₅ and N₂O₄ donor set, respectively. In the dimeric compound 1, the {Cu(9dhx)(H₂O)₃}₂ units are bridged by sulfate groups with the Cu···Cu separation being 5.3446(2) Å. In both structures the 9dhx ligands are coordinated through the N3 atoms of the pyrimidine moieties. The SOD-like activity of complexes 1 and 2 was evaluated in vitro showing moderate effect, with the IC₅₀ values equal to 18.20, and 53.33 μM, respectively.     

Sandwich buckling formulas and applicability of standard computational algorithm for finite strain

Although, for homogeneous columns, the differences between Engesser's and Haringx's formulas for shear buckling have been explained in 1971 by the dependence of shear modulus on the axial stress, for soft-core sandwich columns the choice of the correct formula has baffled engineers for half a century. Recently, Ba ant explained this difference by a variational analysis which showed that an agreement is achieved if the shear modulus of the light core is considered to depend on the compressive stress in the skins even when small-strain elasticity applies. To clarify this paradoxical dependence, first the variational framework is briefly reviewed. Subsequently, the mathematical results from Ba ant's recent study are physically reinterpreted, with the conclusion that only the Engesser-type theory (rather than Haringx-type theory) corresponds to constant shear moduli as obtained, for example, by the torsional test of a tube made from the foam. This is a rather fundamental point for applications because the discrepancy between these two theories can be very large in the case of short columns with thin skins. The implications for standard finite element programs are then explored by computing the critical loads of several sandwich columns with different material and geometric properties. The finite element computations show agreement with the Engesser-type formula predictions, while the Haringx-type prediction can be obtained with the finite element program somewhat artificially—by updating the core modulus as a function of the axial stress in the skins.     

A note on emptiness for alternating finite automata with a one-letter alphabet

We present a new proof of PSPACE-hardness of the emptiness problem for alternating finite automata with a singleton alphabet. This result was shown by Holzer (1995) who used a proof relying on a series of reductions from several papers. The new proof is simple, direct and self-contained.     

Vertex Effect in Strain-Softening Concrete at Rotating Principal Axes

The inelastic behavior of concrete for highly nonproportional loading paths with rotating principal stress axes is studied. Test cylinders are first loaded in compression under uniaxial stress and then torsion is applied at constant axial displacement. Proportional compressive-torsional loading tests are also carried out for comparison. The tests demonstrate that the response of concrete for load increments parallel in the stress space to the current yield surface is highly inelastic (i.e., much softer than elastic) in the peak load range and especially in the postpeak range. The classical tensorial models of plasticity type incorrectly predict for such load increments the elastic stiffness. The experiments are simulated by three-dimensional finite element analysis using the microplane model M4, in which the stress-strain relations are characterized not by tensors but by vectors of stress and strain on planes of various orientations in the material. It is shown that the observed vertex effect is correctly predicted by this model, with no adjustment of its material parameters previously calibrated by other test results. The experiments are also simulated by a state-of-the-art fracture-plastic model of tensorial type and it is found that the vertex effect cannot be reproduced at all, although an adjustment of one material parameter suffices to obtain a realistic postpeak slope and achieve a realistic overall response. What makes the microplane model capable of capturing the vertex effect is the existence of more than 60 simultaneous yield surfaces. Capturing the vertex effect is important for highly nonproportional loading with rotating principal stress axes, which is typical of impact and penetration of missiles, shock, blasts, and earthquake.     

Size Effect on Strength of Quasibrittle Structures with Reentrant Corners Symmetrically Loaded in Tension

The effect of V-notches (or reentrant corners) on fracture propagation has been analyzed for brittle materials, but not for quasibrittle materials such as concrete, marked by a large material characteristic length producing a strong size effect transitional between plasticity and linear elastic fracture mechanics. A simple size effect law for the nominal strength of quasibrittle structures with symmetrically loaded notches, incorporating the effect of notch angle, is derived by asymptotic matching of the following five limit cases: (1) Ba?ant’s size effect law for quasibrittle structures with large cracks for notch angle approaching zero; (2) absence of size effect for vanishing structure size; (3) absence of size effect for notch angle approaching π; (4) plasticity-based notch angle effect for vanishing size; and (5) the notch angle effect on crack initiation in brittle structures, which represents the large-size limit of quasibrittle structures. Accuracy for the brittle large-size limit, with notch angle effect only, is first verified by extensive finite-element analyses of bodies with various notch angles. Then a cohesive crack characterized by a softening stress-separation law is considered to emanate from the notch tip, and the same finite-element model is used to verify and calibrate the proposed law for size and angle effects in the transitional size range in which the body is not far larger than Irwin’s material characteristic length. Experimental verification of the notch angle effect is obtained by comparisons with Dunn et al.’s extensive tests of three-point-bend notched beams made of plexiglass (polymethyl methacrylate), and Seweryn’s tests of double-edge-notched tension specimens, one set made of plexiglass and another of aluminum alloy.     

The High-Temperature Wear and Oxidation Behavior of CrC-Based HVOF Coatings

Three commercially available chromium carbide-based powders with different kinds of matrix (Cr₃C₂-25%NiCr; Cr₃C₂-25%CoNiCrAlY and Cr₃C₂-50%NiCrMoNb) were deposited by an HVOF JP-5000 spraying gun, evaluated and compared. The influence of heat treatment on the microstructure and properties, as well as the oxidation resistance in a hot steam environment (p = 24 MPa; T = 609 °C), was evaluated by SEM and XRD with respect to their potential application in the steam power industry. The sliding wear resistance measured at room and elevated (T = 600 °C) temperatures according to ASTM G-133. For all three kinds of chromium carbide-based coatings, the precipitation of secondary carbides from the supersaturated matrix was observed during the heat treatment. For Cr₃C₂-25%NiCr coating annealed in hot steam environment as well as for Cr₃C₂-25%CoNiCrAlY coating in both environments, the inner carbide oxidation was recorded. The sliding wear resistance was found equal at room temperature, regardless of the matrix composition and content, while at elevated temperatures, the higher wear was measured, varying in dependence on the matrix composition and content. The chromium carbide-based coating with modified matrix composition Cr₃C₂-50%NiCrMoNb is suitable to replace the Cr₃C₂-25%NiCr coating in a hot steam environment to eliminate the risk of failure caused by inner carbide oxidation.     

Self‐Propelled Supercapacitors for On‐Demand Circuit Configuration Based on WS2 Nanoparticles Micromachines

The miniaturization of energy storage microcapacitors to develop portable electronic devices has been of high recent interest. Here, microsupercapacitors microrobot is fabricated using membrane template‐assisted electrodeposition of WS₂ nanoparticles (WS₂NPs)/polyaniline (PANI) and platinum (Pt) layers. The microrobot navigates in the microchannel and attaches itself as part of the electrical circuit. The attached WS₂NPs‐PANI/Pt microrobots enhance the capacitive behavior of the circuit significantly. The results presented in this work open the door for the development of smart and miniaturized functional micromotors that are able to self‐assemble to on‐demand circuits.     

Z Copy‐Controlled Gain‐Current Differencing Buffered Amplifier and its applications

The Z Copy‐Controlled Gain‐Current Differencing Buffered Amplifier (ZC‐CG‐CDBA) is introduced in the paper. In addition to the well‐known CDBA, the input Current Differencing Unit (CDU) is modified and completed by special circuits. Analogously to the conventional CDBA, the z terminal is internally connected to the input of voltage buffer. The current gain from the difference input p, n to the output z can be controlled electronically or by an external device. In addition, an independent high‐impedance output zc is available, providing difference current I_p?I_n. In the paper, the extension of application range of the ZC‐CG‐CDBA compared with the conventional CDBA is referred to. The novel circuit element is assembled from commercial integrated circuits and its principle is verified experimentally on a universal second‐order filter. Copyright © 2010 John Wiley & Sons, Ltd.     

Homogeneous nucleation rate at various initial supersaturations in a closed system

The rate of formation of nuclei in a closed system is studied by numerical solution of kinetic equations at various supersaturations. Depletion of vapor (decrease of supersaturation) due to the phase transition process is taken into account. At a relatively low value of initial supersaturations, the decrease of supersaturation is negligible. At somewhat higher initial supersaturations, the phase transition process is more intense and the decrease of supersaturation plays an important role. As a consequence the nucleation rate after reaching a maximum decreases with time and for sufficiently long times only the nuclei of certain size are formed. At high initial supersaturation the nucleation rate for subcritical cluster sizes is negative, i.e. the number of subcritical clusters tends to get reduced. Critical size increases with time due to lowered supersaturation.