Investigation of isothermal and dynamic cure kinetics of epoxy resin/nadic methyl anhydride/dicyandiamide by differential scanning calorimetry (DSC)

Isothermal and dynamic differential scanning calorimetry (DSC) was exploited to study the curing behavior of diglycidyl ether bisphenol-A epoxy resin with various combining ratios of dicyandiamide (DICY) and nadic methyl anhydride (NMA). Curves of prepared samples indicated that the enthalpy of the reaction decreased with increasing the molar ratios (NMA/DICY) up to 40% after which an exothermic peak peculiar to the effect of anhydride appeared at a higher temperature. The curing behavior examination of the samples containing the aforementioned molar ratio of NMA/DICY (= 40%) was carried out using isothermal condition at different temperatures (130–145 °C) and dynamic condition DSC at various heating rates (2.5–20 °C min⁻¹). Under the isothermal condition, by constructing a master curve, the values of activation energy (E_a) and pre-exponential factor (A) were calculated 89.3 kJ mol⁻¹ and 1.2 × 10⁺⁹ s⁻¹, respectively. The activation energy of the curing reactions in a dynamic mode was obtained 85.32 kJ mol⁻¹ and 88.02 kJ mol⁻¹ using Kissinger and Ozawa methods, respectively. Likewise, pre-exponential factors were also calculated 3.35 × 10⁺⁸ and 7.4 × 10 ⁺⁸ s⁻¹, respectively. The overall order of reaction for both conditions was found to be a value around 3.

     

A novel semi-inverse solution method for elastoplastic torsion of heat treated rods

Torsion rods are a primary component of many power transmission and other mechanical systems. The behavior of these rods under elastoplastic torsion is of major concern for designers. Different methods have so far been proposed which deal with the elastoplastic torsion of rods, most of which assume constant yield stress. This assumption produces rough and inaccurate results when the rods are heat treated, since in the process of heat treatment the form of yield stress distribution across the rod cross section changes. We propose a new method for calculating elastoplastic torsion of rods of simply connected cross section which is based on heat treatment observations. In our method the full plastic stress function is obtained by using the semi-inverse method. Elastoplastic stress function is obtained by generalizing the idea of the membrane analogy and using a piecewise continuous stress function. Since the proposed form of yield stress distribution can not be handled by the current Finite Element packages, we produce a computer package with a 3D graphical interface capable of calculating and displaying the 3D elastoplastic stress function, shear stress contours, and torque-angle of rotation per unit length. We show that our method produces excellent agreement for several known cross sections in comparison to methods which assume constant yield stress.     

Novel multicomponent reactions involving isoquinoline or phenanthridine and activated acetylenic ester in the presence of heterocyclic NH or 1,3-dicarbonyl compounds

Multicomponent reactions involving azines (phenanthridine or isoquinoline) and dimethyl acetylenedicarboxylate were undertaken in the presence of heterocyclic NH compounds (indole, 2-methyl indole, 3-methyl indole, carbazole and 3,6-dibromocarbazole) or 1,3-dicarbonyl compounds such as N,N'-dimethylbarbituric acid, 1,3-diethyl-2-thiobarbituric acid, acetylacetone, 1,3-diphenyl-1,3-propandione and cyclopentan-1,3-dione to generate enaminoesters in good yields.     

Hilbert space factorization and partial measurements

A quantum system whose state vector belongs to a finite-dimensional Hilbert space is considered. If this space has a dimension that is a composite number, one can factor the space into a tensor product of sub-spaces. An observable that acts only in one of these subspaces is called a partial measurement. Some of the properties and the interpretation of such partial measurements are discussed.     

AM1 study of conformations of oxocane and 1,3-dioxocane

Summary AM1 semi-empirical SCF MO calculations are reported for important conformations of oxocane (1) and 1,3-dioxocane (2). The boat-chair conformation of1 (BC-1) is found to be the most stable form, whereas the crown family conformation is calculated to be 3.7 kJ·mol^–1 less stable. The boat-boat form of1 is 15.9 kJ·mol^–1 less stable thanBC-1. The boat-chair conformation of2 (BC-1,3) is calculated to be the most stable form of 1,3-Dioxocane. The crown-family conformation and the boat-boat geometry of this compound are 4.2 and 8.3 kJ mol^–1 less stable thanBC-1,3.

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AM1-Rechnungen zu den Konformationen von Oxocane und 1,3-Dioxocan

Zusammenfassung Die wesentlichen Konformationen von Oxocan (1) und 1,3-Dioxocan (2) wurden mittels semiempirischer AM1-Rechnungen (SCF MO) untersucht. Die Wanne-Sessel-Konformation von1 (BC-1) ist am stabilsten; Konformationen aus der Klasse der Kronen sind um 3.7 kJ·mol^–1 energiereicher. Die Wanne-Wanne-Konformation von1 ist um 15.9 kJ·mol^–1 instabiler alsBC-1. Die Wanne-Sessel-Konformation von2 (BC-1,3) ist das stabilste Konformer von 1,3-Dioxocan. Kronenkonformationen und Wanne-Wanne-Geometrien sind um 4.2 und 8.3 kJ·mol^–1 energiereicher alsBC-1,3.

     

A new wavelet method for solving the Helmholtz equation with complex solution

The Helmholtz equation which is very important in a variety of applications, such as acoustic cavity and radiation wave, has been greatly considered in recent years. In this article, we propose a new efficient computational method based on the Legendre wavelets (LWs) expansion together with their operational matrices of integration and differentiation to solve this equation with complex solution. Because of the fact that both of the operational matrices of integration and differentiation are used in the proposed method, the boundary conditions are taken into account automatically. The main characteristic behind this approach is that it reduces such problems to those of solving a system of algebraic equations which greatly simplifies the problems. As an applied example, “propagation of plane waves” is investigated to demonstrate the validity and applicability of the presented method. © 2015 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 32: 741–756, 2016     

Organocatalytic synthesis of α-hydroxy and α-aminophosphonates

A new and highly flexible procedure is described for the synthesis of α-amino- and α-hydroxy phosphonates. In the presence of a catalytic amount of oxalic acid (10 mol %), trimethyl phosphite reacts with aldehydes or imines (generated in situ from an aldehyde and an amine) to yield the corresponding coupled products in good yield.