RESEARCH JOURNAL OF UNIVERSITY OF ISFAHAN "SCIENCE"
Year:2005 | Volume:21 | Issue:1|Papers Count:11

Electrostatic separation (induction & contac charging) of minerals (conductors and insultors) was investigated experimentally. The results showed that if a mixture of insulator materials of 0.2 t 0.4 mm size contacted with each other, different materials acquired different charges and when they fall in an electrical or gravitational field, they separate from each other. The charge that different materials acquired was in agreement with other's finding. Separation of coductors was not effective by contact charging but was feasible with induction method. The experiment showed that the time of contact had an appreciable role in separation, but the type of metal had no effective role in separation. Separation of particles less than 0.1 mm size was not effective due to their coagulation. Humidity prevented. Charuing and separating of materials, the process was better in dry condition.

In this article, the quantum mechanical formulation in extended phase space has been generalized to the quantized many body systems with degrees of freedom limited to the evolution of classical and quantum mechanical fields. This makes the investigation of such fields possible in phase space. As an example, the problem of vibrating string has been solved using this formalism.

Fabry-Perot interferometer has classically been used for defining'" fine structures of spectral lines. Today it is also used in modem technology such as ultra stable lasers because of its very high resolving power. In this paper Fabry-perot interferometer is briefly discussed and a scanning fabry-perot interferometer is designed and constructed. Also, its construction and operation is explained. Fringes of He-Ne laser, Sodium and Hg sources are formed and studied by this scanning fabry-perot interferometer. Using this instrument, we have conducted some tests and have tried to measure the separation between two sodium lines.

In this paper the planar alignment is considered by using numerical calculations, the effect of the thickness of the slab on the threshold field (Bc) and effect of exerted magnetic field on the maximum distortion (qm) in the center of the sample have been shown. Finally, changes of angle alignment of nematic molecules (q) for a narrow slab in a magnetic field are investigated.

In old times some countries used to coin their coins in the bases of prime numbers and people, as an entertainment, were trying to find out the most amount that cannot be payed with the combination of the belonging coins". This number is known as the Frobenius number. More precisely, let Ak ={a0,a1,….,ak} be a set of natural numbers such that {a0,a1,….,ak }=1. Then the natural number N has a representation in the bases of Ak if there exist {x0, x1 ,..., rk E: No = N U{o} such that N = xoao + x1a1 +...+ xk ak Now, the largest number, which cannot be represented in the above form is called the Frobenius number.In the present paper we try to give a new technique for the calculation of the Frobenius number for certain sets.

Spatial prediction of a Gaussian random field in unmeasured sites based on precise observations is easily carried out. But, in practice, because of measurement errors, data contain noise. We assume that noises are independent random variable with distribution (0,t2)and they are also independent of the interest random field. If parameters of the mean, Govariance function and t2 are known, the optimal predictor and its MSE could be determined by usual methods. But, these methods are not desirable when some of the model parameters are random variables. We use the Bayesian approach to determine the optimal predictor and its MSE.

The aim of the present work is to study the effect of chemical compound of the steel roll on the' force required for rolling in the roll gap. This force is known as "roll force". Mathematical models for calculation of the rolling force merely include parameters for which an exact relation with the roll force is known. Since there is no clear mathematical relation between the chemical compound elements of the plate and the roll force in most of mathematical models, these parameters are not considered. However, in some models these parameters are used as an empirical coefficient. Hence the output of mathematical models contains some error due to these unknown parameters.In this paper, the capability of the neural network in predicting the roll force was examined. The chemical compound of the plate in predicting the roll force without considering any mathematical relation with the roll force was used.

Pitting corrosion of commercially pure aluminum and aluminum metal-matrix composite reinforced with TiB2 particles were investigated in 1M sodium chloride solution. The electrochemical methods used in this investigation were potentiodynamic and potentiostatic techniques. Potentiodynamic polarization tests were carried out in naturally aerated and desecrated solutions using various potential scan rates. The influence of bubbling nitrogen gas in solution arid various potential scan rates were investigated, both for commercially pure aluminum and Al-TiB2 composites. Potentiostatic polarization tests were also carried out to determine the exact critical pitting potentials (Bpit). Results showed that the reinforcing TiB2 particles had no significant influence on critical pitting potential (Epit) of aluminum matrix. The Epit value of AI-3% TiB2 and AI-6% TiB2 was only 10m V lower than pitting potential of commercially pure aluminum. It was also found that during the potentiodynamic polarization tests for AI-TiB2 composites, desecration of solution as well as slow scan rate of potential change was necessary for determining the exact Epit values.

Recently steel producers; have used several different methods to increase properties such as ductility, impact strength and formability. In this regards producing steel with very low amount of inclusion, very small size inclusion and modified inclusion can be mentioned. It should be considered, however, presence of inclusions in steel can have worse effects on corrosion properties and strength of hydrogen damage in H2S included environment. In this research, the API-X52 steel produced by Mobarekeh Steel Co. was used. The steel was melted in a 50kg, medium frequency induction furnace and deoxidation was performed using aluminum. The calcium was added outside of the furnace. The effect of using calcium barrier materials on the morphology control, distribution, amount and size of aluminum oxide inclusions was studied using scanning electron microscope and image analyzing computer program. Displacement of glycerin was used to measure the amount of diffusible hydrogen. Immersed test in sour media was performed on NACE standard and similar media with added thiosulphate ions. The results suggest that thiosulphate ions can be a suitable replacement for H2S gas, at least in research tests. The results also show that reducing and spherical inclusions lead to reducing diffusible hydrogen and corrosion rate.

Recently the number of the Internet users has increased rapidly, and various traffic types are emerged as well. As such, the need for a method for traffic filtering has turned out to be very crucial. An effective method for this purpose is to investigate the traffic content in application layer. To provide such filtering, a proxy server can be utilized. A proxy server performs numerous duties which include network access control and traffic filtering.This paper considers a proxy server with rule based intelligent traffic filtering. To evaluate its performance, the proposed proxy server has been implemented and tested in real situation. The test results show that the server has acceptable performance toward recognizing the content and categorizing of browsed web pages.

This paper investigates text documents regarding their topic density. It has divided them into two groups: dense and sparse documents. Dense documents are texts with a wide domain of topics. They have a high topic density (for example religious books, encyclopedia, magazine archives, etc ). We have shown that a) traditional methods cannot be used for topic specific of dense texts, and b) we can benefit from employing the efficiency of the proposed method (Nasir) for dense texts.In this research, we have used dependency relations, paths, triple databases and statistical text processing methods to extract important words and to insert them into a clustering index. Also a method was described to find the reference of pronouns in dense texts. In addition, based on the suggested methods, a prototype system called Nasir was implemented. The result of the implementation on Persian dense texts shows that the quality of indexing and searching improved significantly.