The purpose of this study was to detect DIFferentially functioning items in the University of Tehran English Proficiency Test (UTEPT) which is a high stake test of English developed and administered by the Language Testing Centre of the University of Tehran. This paper is based on the answers of 400 test takers to the test. All participants earned a master degree either in humanities or science and engineering. To achieve the purpose of this study, the participants were divided into two equal groups. The results of generalized Mantel-Haenszel indicated that out of 100 items 12 items were displaying DIF. Logistic regression procedure also flagged 14 items as exhibiting DIF. Nevertheless, the associated test of effect size for logistic regression showed that none of these effect sizes were large according to the guidelines proposed by both Zumbo and Thomas (1997) and Jodoin and Gierl (2001). Therefore, it was concluded that UTEPT doesn't show significant academic discipline DIF and is equally fair to both humanities and science and engineering groups.

In this study, the asymptotic Adomian decomposition method (AADM) is imple-mented to solve fractional order Riccati di, erential equations. The product integra-tion method is used to solve the singular integrals, resulted from fractional derivative. Some fractional order Riccati di, erential equations are presented as examples to il-lustrate the ability and e, ciency of the proposed approach. The approximate solu-tions of AADM are compared with the results of the Laplace Adomian Pade method (LAPM). Generalizing AADM for solving fractional Riccati di, erential equations by the far-, eld approximation indicates the novelty of the paper.

Identifying distractors as sources of DIFferential Item Functioning(DIF) in polyotomous items has great importance to designers and analysts. Although DIF is one of the common methods for examining the measurement invariance, It is accompanied by challenges and limitations, especially in multiple choice items. The purpose of this study was to assess the performance of Nested logit Model(NLM) for detecting DIFferential Distractor Functioning(DDF) by using experimental (simulated data) and descriptive-analytical (real data) methods. Six items were simulated under DIFferent conditions of DIFficulty and slope, ability distribution, presence or absence of DIF/DDF, and DIF/DDF magnitude, with a sample size of 2000 and 50 replicates. The data of Math Entrance Exam (D-form,2018), with a random sample of 2000 men and women constituted the real data. Based on the results of the simulation analysis: The NLM revealed 88% of DIF and 97% of DDF, on average. the Type I error rates is very close to the theoretical expected values, although it showed some inflation in unequal distribution conditions. according to the findings, the detection rate was influenced by the item parameters(DIFficulty and slope) and the DIF or DDF levels. Based on real data analysis, 2 items represented both DIF(Large and Medium) and DDF (Partial to Moderate) simultaneously, whereas in the NRM approach, 11 items detected as DIF/DDF; so, as expected the approaches based on “divided by distractor” strategy, fewer items were detected as DIF/DDF. The NLM approach, while separating the DDF from the DIF test, allows for a clear evaluation of whether the distractor may be responsible for DIF. Since high-stakes tests have a special role in selection and DIF and DDF analyzes have a special place in determining the validity and measurement invariance of these exam items, it is recommended to screen the bias items, DIF/DDF comprehensive analyzes based on NLM be used.

In this study, the performance of a centrifugal pump is investigated by adding polyacrylamide (PAM) polymer over the working fluid which is tap water in this case. PAM is a long chain polymer that leads to reduce the wall shear stress and drag in a turbulent fluid. Three DIFferent blade profiles including radial, straight backward and circular backward have been examined. For this purpose, a centrifugal pump test rig consists of reservoir, pump-motor, vol-umetric measuring tank, pressure gauges, speed control, and motor dynamometer has been used. DIFferent concentra-tions of PAM polymer solution are prepared in the range of 80-240 ppm of PAM. The results show that the maximum amount of relative efficiency is approximately 3% for the radial propeller, 13% for the straight backward propeller, and 18% for the circular backward which is occurs at 160 ppm of PAM. It is found that this increase is more pro-nounced in the case of circular backward impeller. Moreover, in the case of radial blade profile, it is observed that in spite of efficiency increase, the head decreases at low flow rate with adding PAM.