The power of some standard tests of stationarity against changes in the unconditional variance

Abrupt changes in the unconditional variance of returns have been recently revealed in many empirical studies. In this paper, we show that traditional KPSS-based tests have a low power against nonstationarities stemming from changes in the unconditional variance. More precisely, we show that even under very strong abrupt changes in the unconditional variance, the asymptotic moments of the statistics of these tests remain unchanged. To overcome this problem, we use some CUSUM-based tests adapted for small samples. These tests do not compete with KPSS-based tests and can be considered as complementary. CUSUM-based tests confirm the presence of strong abrupt changes in the unconditional variance of stock returns, whereas KPSS-based tests do not. Consequently, traditional stationary models are not always appropriate to describe stock returns. Finally, we show how a model allowing abrupt changes in the unconditional variance is well appropriate for CAC 40 stock returns.KPSS test, panel stationarity test, unconditional variance, abrupt changes, stock returns, size-power curve.

Technical and vocational skills (TVS): a means of preventing violence among youth in Nigeria

Technical and vocational skills are an important tool for reducing violence among youth, especially in Nigeria, who face security challenges due to different kinds of violence. This paper focusses on the policies and programmes intended to provide youth with skills that can help them improve their life instead of engaging in violence. The paper also studies youth participation in violence. The study shows that youth in Nigeria participate in violence because of unemployment and economic pressure. These youth are mostly from poor families and are mostly used by others to achieve their own unlawful ambition. The data were collected from various secondary sources such as textbooks, journals and conference papers that were carefully reviewed. The results obtained from the literature revealed that youth are not committed, sensitised and mobilised to taking advantage of the opportunities available to them. The results also revealed that almost all the programmes meant to provide youths with skills have failed. Poverty alleviation programmes established to create jobs, self-employment and self-reliance have been unsuccessful. Therefore, alternatives must be provided to help the younger generations. Based on the literature reviewed, the paper discusses related issues and outcomes and ends with recommendations to improve the situation

Steady-state analysis and stability of synchronous reluctance motors considering saturation effects

This paper investigates the influence of the magnetic saturation on the performance of a Synchronous Reluctance Motor (SynRM) at steady-state. In addition, the stability limits for the SynRM are studied using a suggested more accurate method. The saturation and cross-saturation effects on both direct (d) and quadrature (q) axis flux linkages are considered. A Finite Element Method (FEM) is used to obtain an accurate representation for the dq-axis flux linkages relations. In order to reduce the calculation time of the finite element analysis, a look-up table (LUT) for the dq-axis flux linkages is generated based on the FEM to be used for simulating the SynRM characteristics. It is found that the magnetic saturation in the adopted motor results in an enlarged region of stable operation of the SynRM by about 200 % compared with the unsaturated case. The results show the importance of including the saturation factors on the performance of the SynRM and its stability limits. Hence, the magnetic saturation effect will not only reflect on the stability of the motor but also on the whole drive system

On the Capacity Region of the Deterministic Y-Channel with Common and Private Messages

In multi user Gaussian relay networks, it is desirable to transmit private information to each user as well as common information to all of them. However, the capacity region of such networks with both kinds of information is not easy to characterize. The prior art used simple linear deterministic models in order to approximate the capacities of these Gaussian networks. This paper discusses the capacity region of the deterministic Y-channel with private and common messages. In this channel, each user aims at delivering two private messages to the other two users in addition to a common message directed towards both of them. As there is no direct link between the users, all messages must pass through an intermediate relay. We present outer-bounds on the rate region using genie aided and cut-set bounds. Then, we develop a greedy scheme to define an achievable region and show that at a certain number of levels at the relay, our achievable region coincides with the upper bound. Finally, we argue that these bounds for this setup are not sufficient to characterize the capacity region.Comment: 4 figures, 7 page

The analysis of Iran universities’ 2003-2004 entrance examination to detect biased items

Item bias or differential item function (DIF) refers to the situation in which the probability of correct responses to an item for examinees with equal ability measured by test but belong to different groups are not equal. The existence of bias in items decreases the validity of the test. In this study the range of item difficulty among surveyed groups, has been used as a method for detecting the item bias in Persian literature subtest as part of the Entrance Examination to Universities of Iran in 2003-2004. For this purpose, report cards of 5000 (each group of 1000 examinees) participants in this examination from three provinces i.e. Yazd, Azerbaijan Sharghi and Kurdistan as sample groups were analyzed using the computerized program, BILOG-MG. Out of 25, two items, numbers 9 and 10 showed bias between gender groups and both were in favour of female group and were identified as biased items. Of this number, four items numbers 2, 7, 9, and 12 showed bias among linguistic groups

Performance evaluation of synchronous reluctance motors with and without permanent magnets

Nowadays, a growing interest in the efficiency and the cost of electrical machines has been noticed. Therefore, Synchronous Reluctance Motors (SynRMs) have become more attractive, thanks to their higher efficiency and nevertheless acceptable cost compared to induction machines. The rotor design of SynRMs with or without permanent magnets (PMs) has a huge effect on the motor efficiency, torque density and power factor. This paper introduces an evaluation for the performance of SynRMs with and without PMs in terms of efficiency, torque and power factor maps. Three different rotor designs for the same machine have been compared. For one machine, the experimental measurements have been obtained and the validation of the simulation results have been confirme