Nonlocal elasticity in shape memory alloys modeled using peridynamics for solving dynamic problems

Nonlinear Dynamics - The work is primarily devoted to the peridynamic model elaborated for a solid body made of shape memory alloys (SMAs). The superelasticity effect is taken into consideration as...     

Sorption of Sr(II) onto nanocomposites of graphene oxide-polymeric matrix

The simple method for preparation of nanocomposites of graphene oxide or carboxylated graphene oxide on polystyrene matrix and graphene oxide on PA66 matrix were developed and structures of nanocomposites were characterized by X-ray diffraction, infrared spectroscopy, Raman spectroscopy, high-resolution scanning electron microscopy, transmission electron microscopy and scanning transmission electron microscopy. The nanocomposites were investigated for radiostrontium removal from aqueous solutions. The Sr(II) sorption was dependent on pH and ionic strength at pH < 7. The Sr(II) equilibrium data were fitted by Freundlich and Langmuir models. The nanocomposites prepared were evaluated as suitable for the radiostrontium removal from contaminated wastewater.     

Helicenophyrins: Expanded Carbaporphyrins Incorporating Aza[5]helicene and Heptacyclic S‐Shaped Aza[5]helicene Motifs

Incorporation of phenanthrene into a hexaphyrin(1.1.1.1.1.0) frame resulted in intramolecular ring fusion, thus giving rise to chiral helicenophyrins. These molecules contain helicene and porphyrin features by incorporating either an aza[5]helicene or heptacyclic S‐shaped aza[5]helicene.     

On a theorem of Cantor-Bernstein type for algebras

Freytes proved a theorem of Cantor-Bernstein type for algbras; he applied certain sequences of central elements of bounded lattices. The aim of the present paper is to extend the mentioned result to the case when the lattices under consideration need not be bounded; instead of sequences of central elements we deal with sequences of internal direct factors of lattices. This work was supported by Science and Technology Assistance Agency under the contract No APVT-51-032002.     

The effect of magnetic fields on the electrodeposition of iron

The effect of a uniform magnetic field with flux density up to 1 T on the electrodeposition of Fe from sulphate electrolyte has been investigated under different field configurations relative to the electrode surface. Voltammetric and chronoamperometric experiments have been carried out coupled with an electrochemical quartz crystal microbalance for in situ mass change measurements. The structure and morphology of the deposited films were determined by scanning electron microscopy, atomic force microscopy and X-ray diffraction measurements. Results show that, when the magnetic field is applied parallel to the electrode surface, the limiting current density and the deposition rate are increased due to the magnetohydrodynamic effect. The nucleation process is also affected in parallel configuration; the current density of the maximum on the chronoamperograms is decreased, and an additional nucleation step might be observed. This effect is attributed to the hydrodynamic response of the electrochemical system. No significant influence on the electrochemical reaction was observed when a magnetic field was applied perpendicular to the electrode. But in this configuration, the morphology of deposited layers is changed by the magnetic field. The morphology changes are discussed. No effect of the magnetic field on the crystallographic structure was observed.     

A general stereoselective method for the synthesis of cyclopropanecarboxylates. A new version of the homologous Horner-Wadsworth-Emmons reaction

The synthesis of alpha-, beta- and gamma-substituted alpha-phosphono-gamma-lactones was accomplished using different ring closure and ring homologation strategies. It was found that the lactones could be selectively transformed into the corresponding ethyl cyclopropanecarboxylates by treatment with sodium ethoxide in boiling THF. The reported reaction provides an attractive alternative to the classical homologous Horner-Wadsworth-Emmons approach to the construction of cyclopropanes with electron-withdrawing functionalities.     

Stereochemical preference of nucleophillic cleavage in methyl erythrofuranosides explained by density functional theory computations

The nucleophillic substitution is a common method for preparation of saccharide derivatives. For biologically active compounds, it is desirable that the stereochemistry is under control and the amount of byproducts is limited. Therefore, we studied the S_N2 nucleophillic attacks of the azide anion on methyl 2,3-anhydro-α- and -β-l-erythrofuranoside, as well as on their epithio and epimino analogues, which are used as common intermediates in sugar chemistry. Geometry and energetics of the reactions were investigated in the gas phase and in two different solvents using the density functional theory methods. Equilibrium structures of the reactants, reaction-complexes, transition states and products were localized on the computed potential energy surfaces. According to the theory the methoxy group may suppress the substitutions at the 2-position, but detailed reaction rate is influenced by nature of the furanosides and the presence of solvent. Predicted substitution selectivity in the position 2 or 3 of the furanose sugars is in agreement with experimental data.     

Integral geometry analysis of fluorescence micrographs for quantitative relative comparison of protein adsorption onto polymer surfaces

Most methods developed to study protein binding to distinct surfaces can only determine the average amount of adsorbed protein or merely provide (qualitative) information on its spatial distribution. Both these features can be characterized rigorously by integral geometry analysis of fluorescence micrographs. This approach is introduced here to compare the relative protein adsorption onto various polymer surfaces: polystyrene (PS), poly(methyl methacrylate) (PMMA), poly( n-butyl methacrylate) (PnBMA), poly( tert-butyl methacrylate) (PtBMA), and PS(PETA) and cross-linked poly(ethylene oxide) (PEO*(PETA)), admixed with pentaerythritol triacrylate (PETA). The polymeric surfaces were incubated for 15 min in phosphate-buffered saline (pH 7.4) containing 125 mug/mL fluorescently labeled lectins, either lentil lectin (LcH) or concanavalin A (ConA). Fluorescence images were recorded at identical conditions (physiological buffer, same exposure time, magnification, gain). For each image, taken a few times for each polymer, the distribution and average value of the normalized intensity were determined. The results show that the binding of LcH to PS(PETA), PtBMA, PS, PnBMA, PMMA, and PEO*(PETA) can be expressed by the ratio of the following values (mean +/- 95% confidence interval): 0.356 +/- 0.022, 0.298 +/- 0.030, 0.241 +/- 0.014, 0.083 +/- 0.008, 0.039 +/- 0.008, and 0.010 +/- 0.006, respectively. In turn, the relative adsorption of ConA is described by the values 0.252 +/- 0.016, 0.217 +/- 0.014, 0.222 +/- 0.016, 0.046 +/- 0.006, 0.116 +/- 0.008, and 0.006 +/- 0.002, respectively. Low dispersions of fluorescence intensity around average values indicate homogeneous distribution of adsorbed proteins. The introduced approach enables a fast and easy way not only to quantify the relative amount of bound proteins but also to characterize quantitatively the organization of their surface distribution, as demonstrated for patchlike protein adsorption onto the polymer blend surface.     

Breath figures in polymer and polymer blend films spin-coated in dry and humid ambience

We investigate effects of two spin-coating parameters, relative humidity (5% < or = RH < or = 80%) in ambient atmosphere and water content (3 wt % < or = f(H2O) < or = 20 wt %) in solution (rich in tetrahydrofuran), on the structure of breath figures (BF) formed in spin-cast films of polar poly(methyl methacrylate) (PMMA) and PMMA mixed with nonpolar polystyrene (PS). Film morphologies, examined with atomic and lateral force microscopy, are analyzed with integral geometry analysis to yield morphological BF measures. In PMMA, water added to solution has much stronger impact than that from moisture on formed BFs, which could be ordered (with conformational entropy S approximately 0.9-1.0). In PMMA/PS, BFs decorate exclusively polar PMMA domains, resulting in morphologies with two length scales (sub-micrometer BFs and domains >10 microm). This suggests a novel strategy for herarchic structure formation in multicomponent polymer films. In PS/PMMA, BFs are better developed than in pure PMMA spin-coated in identical conditions. These observations show that the air boundary layer facing the spin-cast polymer film (region) is more important than the ambient atmosphere.     

Saw-sedge <Emphasis Type="Italic">Cladium mariscus</Emphasis> as a functional low-cost adsorbent for effective removal of 2,4-dichlorophenoxyacetic acid from aqueous systems

For the first time in the published literature, a study is described concerning the use of the saw-sedge Cladium mariscus (C. mariscus) for adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous systems. Among the experiments carried out, the elemental composition of C. mariscus was determined (C = 48.0 %, H = 7.1 %, N = 0.95 %, S = 0.4 %), FTIR spectroscopic analysis was performed to confirm the chemical structure of the adsorbent, and porous structure parameters were measured: BET surface area (A _BET  = 0.6 m²/g), total pore volume (V _p  = 0.001 cm³/g) and average pore size (S _p  = 6.6 nm). It was shown that the effectiveness of removal of 2,4-D from aqueous systems using C. mariscus depends on parameters of the process: contact time, system pH, mass of sorbent, and temperature. Maximum adsorption was attained for a solution at pH = 3. Further increase in the alkalinity of the tested systems led to a reduction in the effectiveness of the process. The kinetic of adsorption of 2,4-D by C. mariscus was also determined, and thermodynamic aspects were investigated. The experimental data obtained correspond to a pseudo-second-order kinetic model of type 1. Additionally the negative values obtained for ΔHº indicate that the process is exothermic, and the negative values of ΔGº show it to be spontaneous. As the temperature of the system increases the spontaneity of adsorption is reduced, in accordance with the exothermic nature of the process.