An enhanced e-commerce trust model for community based centralized systems

Conventional trust models cannot simultaneously fulfill three major requirements of community based centralized e-commerce systems having a large number of members and economic risk. First, a buyer dealing with a new seller should be able to consult other buyers’ experiences with that seller to make a better decision. Also, a seller with a good reputation should not abuse it by conducting fraudulent transactions. Finally, a buyer with good experience with a seller, even one with a bad reputation, should be able to continue to deal with that seller. This paper introduces a trust-scoring model (Enhanced E-Commerce Trust Model or E2CTM) to address the above requirements. In E2CTM, a trustor uses personal experience with a trustee and input from other trustors about that trustee. To explore the capability of E2CTM, an online electronic auction shopping system was developed to compare its performance with a conventional trust model used by most electronic shopping systems that uses overall gain and loss of all buyers in simulated auctions as evaluation criteria. The results show the advantage of E2CTM, specifically, in terms of overall performance. The improvement is more significant when there is low percentage of fraudulent transactions in the system.     

Application of weighted homotopy analysis method to solve an inverse source problem for wave equation

In this paper, inverse source problem for the wave equation is considered in one dimension with overdetermination condition. To solve this problem, a version of homotopy analysis method, called weighted homotopy analysis method, is introduced and applied. To show accuracy and reliability of the mentioned method, three numerical examples are given.     

A Modified Approach to Predict Pore Pressure Using the D Exponent Method: An Example from an Oil Field,South of Iran

The methodology for pore pressure prediction known as D exponent is a function of an exponent of adjustment that was originally defined for the Gulf of Mexico (Jorden and Shirley, 1966 Jorden, J. R. and Shirley, O. J. 1966. Application of drilling performance data to overpressure detection. J. Pet. Technol., 18: 1387–1394.  [Google Scholar]; Eaton, 1972 Eaton, B. A. 1972. Graphical method predicts geopressures worldwide. World Oil, 7: 100–104.  [Google Scholar]). A limiting factor of this methodology is the definition of the Normal Compaction Trend, which needs to be interpreted from the data (Mouchet and Mitchell, 1989 Mouchet, J. P. and Mitchell, A. 1989. Abnormal pressure while drilling. Manuals techniques 2. Boussens, , France: Elf Aquitaine..  [Google Scholar]). In this study, the D exponent methodology was modified to make it applicable to the Gachsaran formation in an oil field of Ahvaz, Iran. The approach consisted of calculating the ratio between effective stress and the D exponent at each well, in order to find a robust NCT for the entire field, thus reducing subjectivity in the traditional D exponent methodology. Pore pressure determinations from Measured Direct Tests at one well confirm the predictive capability of the approach.     

Application of the dc-Exponent Method for Abnormal Pressure Detection in Ahwaz Oil Field: A Comparative Study

Abstract

There are different methods for detection of abnormal pressure during drilling; one of these methods is the dc-exponent method. In this research, the applicability of the dc-exponent method is investigated for the detection of abnormal pressure zones in Ahwaz oil field in Iran.

Two procedures exist to calculate the amount of abnormal pressure from dc-exponent data: the Rehm-McClendon and Zamora methods. In some oil fields around the world just one of these methods is applicable and the other one provides incorrect results or is inaccurate. Therefore, in this work both methods are applied to six wells in Ahwaz oil field and a comparison is made between the real pressure (detected on the rig) and the results obtained.