Cure kinetics, dynamic mechanical and morphological properties of epoxy resin-Im6NiBr2 system

The aim of this study was to examine effects of a catalyst of Nickel-imidazole, i.e. Im₆NiBr₂ on the cure reaction and network properties of diglycidyl ether of bisphenol A. DSC and FT-IR measurements are carried out on the epoxy resin loaded with 5, 15, and 30 phr of nickel salt to get some insights into the storage stability. It has been concluded that the storage stability has mainly depended on the epoxy composition and was the lowest for the highest level of curing agent. Kinetics of the cure has been described by applying iso-conversional method of Ozawa to scanning DSC data demonstrating that the studied cure reaction is autocatalytic in nature. The Kamal phenomenological approach has been utilized to fit the experimental isothermal DSC data. The model showed a satisfactory fitting of the experimental results at either early stages or at the final steps of the studied cure reaction. Further, the model did not provide a reasonable fitting in the propagation step of polymerization, 0.3 < α < 0.5, possibly due to existence of the additional reaction/s which did not consider in the used model. DMTA is used to find the optimum cure schedule. It has been shown that the sample with a postcure treatment offers the highest value of glass transition temperature (T_g) in the tan δ peak. SEM and X-ray analyses are employed to investigate the fracture surface morphology and to understand the distribution of nickel in the cured samples exhibiting that the nickel is scattered in the continuous phase homogenously. Flexural properties of the sample cured at optimum conditions are also determined.     

Difference Covering Arrays and Pseudo-Orthogonal Latin Squares

A pair of Latin squares, A and B, of order n, is said to be pseudo-orthogonal if each symbol in A is paired with every symbol in B precisely once, except for one symbol with which it is paired twice and one symbol with which it is not paired at all. A set of t Latin squares, of order n, are said to be mutually pseudo-orthogonal if they are pairwise pseudo-orthogonal. A special class of pseudo-orthogonal Latin squares are the mutually nearly orthogonal Latin squares (MNOLS) first discussed in 2002, with general constructions given in 2007. In this paper we develop row complete MNOLS from difference covering arrays. We will use this connection to settle the spectrum question for sets of 3 mutually pseudo-orthogonal Latin squares of even order, for all but the order 146.     

Synthesis of 1,2,4,5-tetrasubstituted imidazoles using silica-bonded propylpiperazine N-sulfamic acid as a recyclable solid acid catalyst

A simple and efficient procedure for the preparation of silica-bonded propylpiperazine-N-sulfamic acid (SBPPSA) by the reaction of 3-piperazine-N-propylsilica (3-PNPS) and chlorosulfonic acid in chloroform is described. Silica-bonded propylpiperazine-N-sulfamic acid is employed as a recyclable catalyst for the synthesis of highly substituted imidazoles from the reaction of benzil, aromatic aldehydes, ammonium acetate and amines under solvent-free conditions. The heterogeneous catalyst was recycled for five runs upon the reaction of benzil, 4-methylbenzaldehyde, benzylamine, and ammonium acetate without losing its catalytic activity.     

Comparison of photosynthetic components of wheat genotypes under rain-fed and irrigated conditions

The major environmental factor limiting the range of adaptation for wheat is drought. Fourteen wheat genotypes (Triticum aestivum L.) were grown under two environments (irrigated and rain fed) to determine physiological and photosynthetic responses to drought. Combined analysis of variance of the data showed that the environment was a significant source of variation for leaf chlorophyll content (LCC), stomatal conductance (g(s)) and grain yield (GY). Wheat genotypes differed significantly for LCC, g(s) and GY. All the measured traits under water-stress conditions except maximum photochemical efficiency of PSII (F(v)/F(m)) were lower than those under nonstress conditions. Mean GY in rain-fed conditions was 11.26% lower than that in irrigated conditions. The genotypes number 13 (Marvdasht) and 8 (M-81-13) exhibited the highest GY per unit area in both irrigation and rain-fed conditions. It was concluded that the higher LCC and g(s) under drought-stress conditions could possibly be the proper criteria for screening the drought-tolerant wheat genotypes under field conditions.     

Reaction kinetics of a novel thermoset nanocomposite: the glycerol diglycidyl ether/3,3-dimethylglutaric anhydride/nano-Al2O3 system

Abstract  

The curing behavior of the glycerol diglycidyl ether/3,3-dimethylglutaric anhydride/nano-alumina system was examined using a dynamic differential scanning calorimetry technique. The activation energy of the system was calculated using the Kissinger, Ozawa, Barrett, and two-parameter Sestak–Berggren models. Under the assumption of a constant activation energy and an autocatalytic mechanism, the activation energy, frequency factor, and total order of reaction were computed. The theoretical reaction rate was also calculated and compared to the experimental results. Good agreement was seen between the experimental and calculated data confirming the autocatalytic mechanism. The effect of triethylamine concentration on the reaction rate was clarified using the Barrett method. Fourier transform infrared spectroscopy (FT-IR) spectroscopy was used to verify the formation of internal ester groups. Scanning electron microscopy (SEM) and X-ray mapping analyses revealed that the nanofiller was homogeneously distributed in the continuous phase.     

硅胶键合的N-丙基三亚乙基四胺氨基磺酸作为可回收固体酸催化剂催化合成2-氨基-4,6-二芳基烟腈(英文)

A simple and efficient procedure for the preparation of silica-bound N-propyl triethylenetetramine sulfamic acid(SBPTETSA) by the reaction of silica-bound N-propyl triethylenetetramine(SBPTET) with chlorosulfonic acid in chloroform is described.Silica-bound N-propyl triethylenetetramine sulfamic acid was employed as a recyclable catalyst for the synthesis of 2-amino-4,6-diarylnicotinonitriles from the multi-component reaction of an acetophenone derivative,an aromatic aldehyde,malononitrile,and ammonium acetate under solvent-free conditions at 100 °C.The heterogeneous catalyst was recycled for five consecutive runs in the optimized multi-component reaction of 4-chloroacetophenone,4-chloroenzaldehyde,malononitrile,and ammonium acetate without significant loses to its catalytic activity.     

Electrical beam steering with metal-anisotropic-metal structure

In this numerical study, we present and demonstrate a compact, electrical plasmonic beam-steering device composed of anisotropic material. The splitting angle can be modulated by the external electric or magnetic field. The physical principle of this phenomenon is evaluated from the phase of surface plasmon polaritons and Fabry-Perot (F-P) resonance in slits. Our numerical simulations with finite-difference time-domain (FDTD) technique reveals that wide-angle (±27°) beam steering can be achieved. Moreover, the efficiency increases when increasing the steering angle. A special characteristic of the presented structure gives an opportunity to be used as an efficient element in a high integrated optical device for miniaturization and tuning purposes.     

Roman domination subdivision number of graphs

A Roman dominating function on a graph G = (V, E) is a function f : V ? {0, 1, 2}f : V \rightarrow \{0, 1, 2\} satisfying the condition that every vertex v for which f(v) = 0 is adjacent to at least one vertex u for which f(u) = 2. The weight of a Roman dominating function is the value w(f) = ?_{v ? V} f(v)w(f) = \sum_{v\in V} f(v). The Roman domination number of a graph G, denoted by _gR(G)_{\gamma R}(G), equals the minimum weight of a Roman dominating function on G. The Roman domination subdivision number sd_gR(G)sd_{\gamma R}(G) is the minimum number of edges that must be subdivided (each edge in G can be subdivided at most once) in order to increase the Roman domination number. In this paper, first we establish upper bounds on the Roman domination subdivision number for arbitrary graphs in terms of vertex degree. Then we present several different conditions on G which are sufficient to imply that $1 \leq sd_{\gamma R}(G) \leq 3$1 \leq sd_{\gamma R}(G) \leq 3. Finally, we show that the Roman domination subdivision number of a graph can be arbitrarily large.     

An Expedient Synthesis of Novel Derivatives of Pyrido[2,3‐d]pyrimidines Using Magnetically Supported ZrO2 Nanocatalyst

An efficient synthesis of pyrido[2,3‐d]pyrimidine derivatives via one‐pot multicomponent reactions of 6‐amino‐2‐(alkylthio)pyrimidin‐4(3H)‐one, 3‐cyanoacetylindole and arylaldehydes using [Fe₃O₄@ZrO₂] as magnetically recyclable nanocatalyst is reported. This protocol furnished the desired products in good to excellent yields (70–93 %) and lower reaction times. The catalyst could be easily and efficiently separated from the final product solution by an external magnet and be reused in 5 consecutive runs without any significant activity decrease.