Influence of the magnetic field on merging flow of the Powell-Eyring fluids: an exact solution

In this article, the merging flow of the stagnation point and the stretching (or shrinking) flows for the Powell-Eyring fluid (one of the non-Newtonian fluids) in the presence of magnetic field is formulated and analyzed mathematically. An analytical solution was developed on the basis of the homotopy analysis method. The effect of the Hartmann number on fluid-velocity and skin-friction is examined. It is observed that the intensive magnetic field reduces the growth of the reverse/secondary flow which is generated after the mixing of the stagnation-point and shrinking-sheet flows. The magnetic force dominates on the viscous force for stretching as well as for shrinking flows. Furthermore, the magnetic force intensifies the axial velocity of the fluids (the Newtonian as well as the Powell-Eyring fluids) but it decays the transverse-velocity of the fluids. Present results are validated with the existing results for the Newtonian fluids and found comparable with negligible errors.     

Characterization of fluid flow patterns and heat transfer in horizontal channel mixed convection

Two mechanisms of roll initiation are highlighted in a horizontal channel flow, uniformly heated from below, at constant heat flux (Γ = 10, Pr = 7, 50 ≤ Re ≤ 100, 0 ≤ Ra ≤ 10⁶). The first mechanism is the classical one, it occurs for low Rayleigh numbers and is initiated by the lateral wall effect. The second occurs for higher Rayleigh numbers and combines the previous effect with a supercritical vertical temperature gradient in the lower boundary layer, which simultaneously triggers pairs of rolls in the whole zone in between the two lateral rolls. We have found that in the present configuration, the transition between the two roll initiation mechanisms occurs for Ra/Re ² ≈ 18. Consequently, the heat transfer is significantly enhanced compared to the pure forced convection case owing to the flow pattern responsible of the continuous flooding the heated wall with cold fluid.     

Liquid‐crystalline azobenzene‐containing ferrocene‐based polymers: study on synthesis and properties of main‐chain ferrocene‐based polyesters with azobenzene in the side chain

Ferrocene‐based polymers are characterized by their electrochemical activity, good redox properties, thermal, photochemical stability, and liquid crystallinity, and thus they have various applications in different fields. A comprehensive investigation on the synthesis and properties of three novel main‐chain ferrocene‐based polyesters with azobenzene in the side chain (MFPAS) was carried out. The main‐chain ferrocene‐based polyester, poly(N‐phenyldiethanolamine 1,1′‐ferrocene dicarboxylate (PPFD), was synthesized via the solution polycondensation reaction of 1,1′‐ferrocenedicarbonyl chloride with phenyldiethanolamine (PDE). The novel MFPAS were synthesized via the post‐polymerization azo‐coupling reaction of PPFD with three different 4‐substituted anilines including 4‐nitroaniline, 4‐aminobenzoic acid, and 4‐aminobenzonitrile to produce 4‐nitrophenylazo‐functionalized‐PPFD (PPFD‐NT), 4‐carboxyphenylazo‐functionalized‐PPFD (PPFD‐CA), and 4‐cyanophenylazo‐functionalized‐PPFD (PPFD‐CN), respectively. All the synthesized polymers were characterized by ¹H NMR spectroscopy, Fourier transform infrared spectroscopy, and UV–visible spectroscopy. In addition, powder X‐ray diffraction patterns were measured for the synthesized polymers. The photoisomerization of the MFPAS was studied. The thermal properties of the MFPAS were studied using thermogravimetric analysis and differential scanning calorimetry. PPFD‐CA and PPFD‐CN were found to be more thermally stable than PPFD‐NT. Finally, the liquid‐crystalline properties of PPFD and the MFPAS were examined using polarized optical microscope. It was found that all the polymers possessed nematic phases and exhibited textures with schlieren disclinations. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and Characterization of Poly[bis(p-oxybenzaldehyde diethylamino)phosphazenes], Poly[bis(p-oxybenzaldehyde)phosphazenes], Poly[bis(diethylamino)phosphazenes] and their Self- assembly Behaviors

Polydichlorophosphazenes (PDCP) were synthesized through ring opening polymerization of hexachlorocyclotriphosphazene (HCCP). The polymerization behavior of HCCP under varying conditions of time and amount of catalyst was investigated. The chlorine atoms in polydichlorophosphazenes (PDCP) were substituted with p-oxybenzaldehyde and (or) diethylamine to synthesize poly[bis(p-oxybenzaldehyde diethylamino)phosphazenes](PPOBADEAP), poly[bis(p-oxybenzaldehyde)phosphazenes] (PPOBAP) and poly[bis(diethyl amino) phosphazenes] (PDEAP). The supporting evidence for the success of this synthesis was provided by nuclear magnetic resonance (¹H-NMR, and ³¹P-NMR), gel permeation chromatography (GPC), and energy-dispersive X-ray spectroscopy (EDAX). The self-assembly behavior of PPOBADEAP, PPOBAP and PDEAP was observed in different solvents by the same concentration of polymers. The optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images indicated that PPOBADEAP formed various morphologies in different solvents while PPOBAP and PDEAP did not show self-assembly behavior at the same conditions.     

A Novel ‘Domino‐Click Approach’ to Unsymmetrical Bis‐1H‐1,2,3‐triazoles

Aryl azides 1 were treated with allenylmagnesium bromide ( 2 ) to generate 1,5‐disubstituted butynyl‐1H‐1,2,3‐triazoles 3 in a domino fashion, which upon Cu^I‐catalyzed 1,3‐dipolar cycloaddition with aryl azides 4 afforded novel bis‐1H‐1,2,3‐triazoles 5 in quantitative yields (Scheme 1 and Table).     

Natural and semisynthetic polymers blended orodispersible films of citalopram

Abstract

This study was aimed at developing orodispersible films of citalopram using combination of natural and semisynthetic polymers for patients with swallowing problem. Okra biopolymer and moringa gum were utilized in combination with hydroxypropyl methylcellulose (HPMC) and pullulan. The disintegration time was less than 30?seconds and the drug content uniformity was 97.89–102.05% for all film formulations. Films formulated with HPMC (K15 and K4M) combination (F1) and combination of okra and HPMC K15 (F2) had superior mechanical properties as compared with F3 (okra and pullulan) and F4 (moringa gum and HPMC). Thermal analysis revealed stable formulations over the studied temperature range and the crystalline citalopram was completely or partially transformed into amorphous form as revealed by the differential thermal analysis, X-ray diffraction and scanning electron microscopy images. In conclusion, okra biopolymer could be used in combination with HPMC for the development of orodispersible films.     

Capital adequacy and risk management in banking industry

The present paper deals with the issue of bank capital adequacy and risk management within a stochastic dynamic setting. In particular, an explicit risk aggregation and capital expression is provided regarding the portfolio choice and capital requirements special context. Such a framework leads to a nonlinear stochastic optimal control problem whose solution may be determined by means of dynamic programming algorithm. The pertaining analysis relies heavily on the stochastic dynamic modeling of such balance sheet items as securities, loans, and regulatory capital with stochastic interest rates. In this respect, the special Kalman filter approach is used for the purpose of estimating the model parameters. The reached findings reveal well that the Tunisian bank, subject of study, generally exceeds the minimum requirements and is adequately capitalized to maintain the appropriate capital amount level commensurate with the aggregate risk. Besides, empirical evidence on the regulations' impact on driving bank capitalization and risk‐taking behavior has also been highlighted. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis,Structure and Physical Properties of an Hybrid Compound Based on Strandberg Type Polyoxoanions and Copper Cations

Single crystals of novel Strandberg type molybdophosphonate complex, (C₅H₇N₂)₆[Cu(H₂O)₃HP₂Mo₅O₂₃]₂·4H₂O, are synthesized in aqueous solution and characterized by X-ray diffraction, spectroscopy (diffuse reflectance, UV–Vis and IR) and thermal analysis. Single crystal X-ray diffraction analysis reveals that this novel compound is composed of [Cu(H₂O)₃HP₂Mo₅O₂₃]^3? anions, three distinct 2-aminopyridinium cations as counter-ions and two distinct crystallization water molecules. The crystal packing is stabilized by H-bonds and π–π interactions, resulting in a 3D framework. In addition, the magnetic behavior of the related compound is measured. Magnetic measurements from 100 to 2 K indicate the presence of an antiferromagnetic coupling between the Cu (II) ions in (C₅H₇N₂)₆[Cu(H₂O)₃HP₂Mo₅O₂₃]₂·4H₂O complex, resulting in a maximum of an antiferromagnetic–paramagnetic transition at T_N = 7 K. Magnetic susceptibility data indicate an antiferromagnetic Curie–Weiss behavior in the studied temperature range, and molecular field theory gives the (J/k_B) values of the nearest neighbor interactions between copper ions.