نشریه علوم پایه
سال بیستم شماره 1 (1386)

The notion of "universal algebra'' is in fact a generalization of the familiar algebraic notions such as groups, rings, vector spaces. Some mathematicians, for example, Whitehead and Noether realized the importance of introducing this notion and finally in 1993 Birkhoff gave the first definition. Now a days universal algebra not only has achieved its first goals but also plays an important role in some modern areas such as. automata, and computer scienceOne of the goals of universal algebra is to consider the common and similar notions and properties of classic algebraic structures in a general and more abstract framework. For this reason, in the context of universal algebra some notions such as subalgebra, quotient algebra, homomorphism, direct product, and free algebra are defined, and Isomorphism Theorems are proved in general.In this paper, we intend to bring the basic definitions and results of universal algebra.

In this study different solvent treatment procedures were employed and comparatively evaluated for purification of crude anthracene cake obtained from Esfahan (Iran) Coal Tar Refinery. Prior to purification, the composition of the crude anthracene cake was found by GC analysis, in which 21 impurities with different percentages were detected. The main contents are anthracene, carbazole and phenantherene. By employing 16 different and individual solvents, efficiencies of them based on the purity and yield of anthracene were found. The results showed that it is possible to recover anthracene from crude anthracene cake with a yield and purity of 92% and 98%, respectively

A simple method for synthesis of sulfo benzyl silica is presented. Silicagel was dehydrated at 400oC temperature, then the dehydrated silicagel reacts with benzyl magnesium chloride to produce benzyl silica. Benzyl silica is treated with Chloro Sulfonic Acid to produce sulfo benzyl silica. Application of sulfo benzyl silica as a heterogeneous acidic catalyst was investigated in synthesis and hydrolyis of ethyl acetate.

The aim of this work is to study the basic principles, which govern the operations of quantum well lasers. One of the keys for understanding these underlying principles requires a basic comprehension of the single quantum well and its characteristics like the gain. Optical gain characteristics of quantum well lasers are investigated in a broad range in a weakly quantized model with k selection rule. This model, based on Kane's two band model, solves to find the constant energy surfaces. Here, the investigated system was GaAs/Al0.2Ga0.8As as quantum well structures at 300 K. In this work, we investigate theoretically a number of important issues related to the performance of quantum well semiconductor lasers, which include derivation of gain in quantum well lasers structures. The maximum gain as a function of emission photon energy and modal gain with confinement factor in cavity lasers are calculated and drawn.

The cocept of hyperrings first was introduced by Krasner in 1966. Since then this subject has been studied and investigated by many arbors. In this paper, we introduce the notion of hyperrings and by using the notious of hyperidoal, strong homomorphism and quolient hyperring. We prove the first, second and third isomorphism theorems for hyperrings. Finally, we define the fundamental equivalence relation γ on hyperrings (the relation that make a connection between hyperrings and ordinarv rings) and we prove some results in this respect.

As we know structures behave in different fashion under climate variation and the most responsible for these variations is heat which falls through and causes deformation of the body. The present paper deals with the problem of two exterior Griffith cracks opened by heated wedge in a strip whose edges are normal to crack axis and the medium is assumed to be homogen and isotrop. Under plain strain condition the closed form expressions for physical quantities such as normal stress components, stress intensity factors and the crack shape are obtained by using the Fourier sine and cosine transformation.

A new method for measurement the small signal gain of an open CW-CO2 laser in different condition is presented and the theoretical concepts are completely described. This method is based on bringing the laser on critical condition by inserting a loss element in laser cavity. Also, by measuring output power, in a same time, the gain saturation intensity for each condition is obtained. The main point of this method is removing requirement to additional laser that has been used for measuring of small signal gain in oscillator amplifier method. With Inter- Cavity loss element method, easer than classic method, results have been obtained which are comparable with other’s.