Nonlinear transient dynamic response of damped plates using a higher order shear deformation theory

Damped transient dynamic elasto-plastic analysis of plate is investigated. A finite element model based on a C ⁰ higher order shear deformation theory has been developed. Nine noded Lagrangian elements with five degrees of freedom per node are used. Selective Gauss integration is used to evaluate energy terms so as to avoid shear locking and spurious mechanisms. Von Mises and Tresca yield criteria are incorporated along with associated flow rules. Explicit central difference time stepping scheme is employed to integrate temporal equations. The mass matrix is diagonalized by using the efficient proportional mass lumping scheme. A program is developed for damped transient dynamic finite element analysis of elasto-plastic plate. Several numerical examples are studied to unfold different facets of damping of elasto-plastic plates.     

Polyfluorophenylaminosilane–Titanium (IV) Chloride Adducts

Si(NHC₆H_5-nF_n)₄.xTiCl₄ [n = 2–5; x = 3,4] are obtained from the disproportionation reactions between (CF₃CH₂O)₃SiNHC₆H_5-nF_n (n = 2–5) and TiCl₄ in petroleum ether (40–60°C) at 0°–10°C. These complexes are characterized by elemental analyses and IR, ¹H, and ¹⁹F NMR spectroscopy. Unlike the reported⁵ complex Si(NHC₆H₄F-o)₄.3TiCl₄, these are non-ionic in nature. All complexes give double adducts with CH₃NO₂ and CH₃CN within 24 h.     

Chemical constituents of Nepalese propolis (II)

A novel flavanonol (1), three new isoflavones (2-4) and a new flavan-3-ol (5) were isolated along with ten other known flavonoids (6-15) from the methanolic extract of propolis collected from Chitwan, Nepal. Their structures were determined on the basis of spectral analysis.     

Iron chelation equilibria, redox, and siderophore activity of a saccharide platform ferrichrome analogue

A complete characterization of the aqueous solution Fe(III) and Fe(II) coordination chemistry of a saccharide-based ferrichrome analogue, 1-O-methyl-2,3,6-tris-O-[4-(N-hydroxy-N-ethylcarbamoyl)-n-butyryl]-alpha-D-glucopyranoside (H3LN236), is reported including relevant thermodynamic parameters and growth promotion activity with respect to both Gram-negative and Gram-positive bacterial strains. The saccharide platform is an attractive backbone for the design and synthesis of ferrichrome analogues because of its improved water solubility and hydrogen-bonding capabilities, which can potentially provide favorable receptor recognition and biological activity. The ligand deprotonation constants (pKa values), iron complex (FeIII(LN236) and FeII(LN236)1-) protonation constants (KFeHxL-236-N), overall Fe(III) and Fe(II) chelation constants (beta110), and aqueous solution speciation were determined by spectrophotometric and potentiometric titrations, EDTA competition equilibria, and cyclic voltammetry. Log betaIII110 = 31.16 and pFe = 26.1 for FeIII(LN236) suggests a high affinity for Fe(III), which is comparable to or greater than ferrichrome and other ferrichrome analogues. The E1/2 for the FeIII(LN236)/FeII(LN236)1- couple was determined to be -454 mV (vs NHE) from quasi-reversible cyclic voltammograms at pH 9. Below pH 6.5, the E1/2 shifts to more positive values and the pH-dependent E1/2 profile was used to determine the FeII(LN236)1- protonation constants and overall stability constant log betaII110 = 11.1. A comparative analysis of similar data for an Fe(III) complex of a structural isomer of this exocyclic saccharide chelator (H3LR234), including strain energy calculations, allows us to analyze the relative effects of the pendant arm position and hydroxamate moiety orientation (normal vs retro) on overall complex stability. A correlation between siderophore activity and iron coordination chemistry of these saccharide-hydroxamate chelators is made.     

Oil-induced anomalous thermoresponsive viscoelasticity in fluorinated surfactant systems

We have studied the rheology and structure of a mixed nonionic fluorinated surfactant, perfluoroalkyl sulfonamide ethoxylate, C(8)F(17)SO(2)N(C(3)H(7))(CH(2)CH(2)O)(n)H abbreviated as C(8)F(17)EO(10), and perfluorodecalin (C(10)F(18)) or perfluoropolyether oil, (C(3)F(6)O)(n)COOH, in an aqueous system using rheometry and small-angle X-ray scattering (SAXS) techniques. In the absence of oil, the viscosity of surfactant solutions (10 and 15 wt %) first decreases slightly and then more strongly with temperature. Addition of a small amount of fluorinated oil to the wormlike micellar solution disrupts the network structure and decreases the viscosity sharply at lower temperature indicating a rod-sphere transition. The trend of the viscosity curve changes gradually and an anomalous viscosity maximum as a function of temperature appears. It is found that perfluoropolyether oil decreases the viscosity more effectively than perfluorodecalin. The generalized indirect Fourier transformation (GIFT) analysis of the SAXS data confirmed the formation of long rod-like particles in an oil-free, surfactant/water system at 20 degrees C. Addition of a trace amount of fluorinated oils induces modulation in the structure of the micelles and eventually short rods or spherical particles are formed. The decreasing trend in the viscosity with oil concentration is thus attributed to the microstructure changes induced by the added oils.     

Physico-chemical studies in non-aqueous solvents: Part XII. Thermochemical studies of some 1:1 electrolytes in N,N-dimethylacetamide

Heats of solution of alkali metal, silver, ammonium and substituted ammonium perchlorates, lithium chloride and potassium thiocyanate have been measured in the concentration range 1.26–112.8×10^?3 mol l^?1 in N,N-dimethylacetamide (DMA) at 26.9°C. Slopes of the linear plots of heat of solution vs. square root of concentration are two to three times higher than the Debye-Hückel limiting slope indicating thereby complete dissociation of the electrolytes. Standard heats of solution of the electrolytes in DMA are higher than those in formamide and N-methylformamide and are comparable to those in N,N-dimethylformamide. Buckingham's model has been used to determine the solvation enthalpies of various ions in this solvent. The results indicate that ion solvation enthalpies decrease with increase in size of the ions and that the anion solvation enthalpies are higher than cation solvation enthalpies which is consistent with the findings in various solvents.     

Reaction Between Bis(Dichlorophosphoryl)Imide and Hexamethyldisilazane

By reaction between bis(dichlorophosphoryl)imide and hexamethyldisilazane – with or without solvent – the authors obtain two phases. The solid phase is the ammonium salt of the bis(dichlorophosphoryl)imide which can be obtained, like many other metallic salts of this type, by the general reaction: . The salt is characterized by its I.R., and ³¹P, ¹H, and ¹⁴N N.M.R. spectra and by its hydrolysis reaction. The composition of the liquid phase changes according the experimental conditions. It seems that at first the main components are Cl₂(O)P? N?P(OSiMe₃)Cl₂ and Cl₂(Me₃SiO)P?N? PCl(OH)NSiMe₃. These compounds condense further to high polymers.