Strain field and extrusion load in ECAE process of bi-metal circular cross section

In this paper the previous velocity field proposed by the authors for the prediction of strain field and deformation load of circular cross section billet in ECAE process has been extended to take into account the deformation behavior of bimetal circular billet in the same process. Accordingly, using Bezier method, as a robust method for determining the geometry of the streamlines, the strain field developed in the circular bimetal billet is calculated. Then, based on the kinematically admissible velocity and strain fields and using the upper bound theorem the ECAE load is predicted. It was found that at constant inner corner angle of ECAE die, with decreasing of outer curve corner the inhemogenity of strain distribution is decreased and the ECAE force is increased. Also, at a constant outer curve corner, by decreasing the inner corner angle, the extrusion load is increased. A good agreement was found between the predicted and experimental results.     

Electrodialysis of oxalic acid: batch process modeling

Batch electrodialysis of aqueous solutions of oxalic acid was investigated using a laboratory electrodialyzer ED-Z mini equipped with ion-exchange membranes Ralex-AMH-PES and Ralex-CMHPES (Mega, Strá? pod Ralskem, Czech Republic). The paper presents a mathematical model which enables to predict changes in the oxalic acid concentrations in the diluate and concentrate compartments during the electrodialysis process under various conditions specified by combinations of the initial acid concentrations with current densities. The calculation proved a good agreement between the developed model and the experimental results.     

Continuous wave mirrorless lasing in cholesteric liquid crystals with a pitch gradient across the cell gap

Despite numerous efforts, continuous wave (CW) lasing in dye doped, one-dimensional (1D) photonic bandgap cholesteric liquid crystal (CLC) structures has not been previously reported, to our knowledge. Here we report on the observation of lasing in such structures under both coherent (laser) and incoherent (LED) CW light excitation. To achieve this effect, we used a 1D-photonic bandgap structure made of a polymer stabilized CLC with a pitch gradient across the cell thickness. A spectral reflectivity profile of such a CLC structure reveals local minima in the area within a photonic stopband and close to it. The realization of lasing pumped by low power CW light sources opens the possibility of all-organic, compact, tunable CW lasers for display and medical applications.     

On factor-invariant graphs

We classify trivalent vertex-transitive graphs whose edge sets have a partition into a Hamilton cycle and a 1-factor that is invariant under the action of the full automorphism group.     

Organic–inorganic hybrid of anchored dicationic ionic liquid on Al‐MCM‐41‐phosphovanadomolybdate toward selective oxidation of benzene to phenol

A phosphovanadomolybdate hybridized with an anchored dicationic ionic liquid on Al‐MCM‐41 was prepared through the anion exchange and characterized by ¹H and ¹³C NMR, FTIR, UV–Vis, XRD, XPS, TGA, TEM, FESEM, ICP‐OES and BET techniques. The obtained data demonstrated that the composite is a porous material with the high surface area and also having a large pore volume which are 405 m² g^?1 and 0.616 cm³ g^?1 respectively. The prepared composite has shown an acceptable catalytic activity for converting benzene selectively to phenol with hydrogen peroxide as eco‐friendly oxidant. Under the optimized reaction conditions, the hybrid catalyst resulted in phenol yield of 14.8% with 100% selectivity and a TOF value of 20.0 h^?1. The catalyst also revealed a desired recovery and reusability. The efficient performance of the composite is related to the textural and polyoxometalate properties.     

Electrocatalytic reduction of Molecular Oxygen with a Copper (II) Coordination Polymer

Oxygen reduction at the polarized water/1,2-dichloroethane (DCE) interface catalyzed by a Cu (II) coordination polymer (Cu–pol) was studied with two lipophilic electron donors ferrocene (Fc) and tetrathiafulvalene (TTF). The results of the ion transfer voltammetry and two-phase shake flask experiments suggest proceeding of the catalytic reaction as proton-coupled electron transfer reduction of oxygen to hydrogen peroxide and water. In this process, while the protons supplied from the aqueous phase, the electrons provided from the organic phase by the weak electron donor, Fc. The O₂ molecule takes a superoxide structure with Cu–pol which resulted to hydrogen peroxide or water on reduction. Furthermore, the results revealed that the apparent rate constant of TTF + Cu-pol is higher than that of Fc + Cu-pol system due to the faster kinetic reaction of TTF with respect to Fc.     

The effect of buffer concentration and cation type in the mobile phase on retention of amino acids and dipeptides in hydrophilic interaction liquid chromatography

The current work is focused on exploring the effect of buffer cation type and its concentration on retention of amino acids, dipeptides and their blocked analogues on two stationary phases, i.e., bare silica and amide-based in hydrophilic interaction liquid chromatography. Five different buffers of pH 4.0 composed of Tris/acetic acid, triethylamine/acetic acid, ammonium/acetic acid, Li⁺/acetic acid and Ba²⁺/acetic acid were used in various concentrations. Interestingly, an increase of the buffer concentration caused increasing, decreasing or stable retention of analytes, according to the cation type in the buffer. The buffers containing barium cations provided the highest retention of all the analytes in comparable mobile phases, i.e., buffers with the same ionic strength and pH on both columns. Moreover, using buffers with barium cation different selectivity for dipeptides was observed. The chromatographic systems with buffers consisting of triethylamine behaved differently compared to others.     

Determination of pKa values for (E)-2-hydroxy-5-(aryldiazenyl) benzaldehydes in dimethyl sulfoxide: Cyclic voltammetry and density functional theory calculations

The (E)-2-hydroxy-5-(aryldiazenyl) benzaldehydes (azo dyes 1–4 ) were synthesized in high purity. As they are insoluble in water, the usual analytical methods cannot be utilized to determine their pK_a values. Cyclic voltammetry was experimentally used to determine their pKa values in DMSO solvent. In addition, computational methods and a conductor-like screening model (COSMO) were used to calculate the solvent effect. , , K_exchange, and pK_a values were estimated for the azo dyes being studied using the BP86, TPSS, B3LYP, PBE0, TPSSh, and PW6B95 density functionals in def2-TZVP basis sets. The obtained mean absolute deviations (MADs) indicate that the results of BP86, PBE0, and PW6B95 functionals are in good agreement with experimental values.