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

Study of heterosis in single-cross hybrids of sunflower

    This study was conducted to estimate the genetic variability and heterosis of 40 F1 hybrids of sunflower for seed yield and its components over two seasons (summer and winter) in 2007 at Sennar Research Station Farm in central Sudan. The plant material consisted of 14 sunflower parents            (4 females and 10 males) and their 40 F1-hybrids. The experiment was arranged in a randomized complete block design with three replicates. The traits measured were days to 50% flowering, plant height, head diameter, number of seeds per head, one thousand seed weight and seed yield.  Hybrids showed high genetic variability for all traits studied than their parents which suggested some degree of hybrid vigor. The direction and magnitude of heterosis varied from cross to cross. Over two seasons, the average mid-parent heterosis in preferred direction and magnitude depicted that the hybrid SA2 x SR41 followed by SA3 x SR41 for days to flowering, SA1 x SR14 for plant height, SA2 x SR14 for head diameter, SA2 x SR13 followed by SA3 x SR13 for number of seeds per head, and SA3 x SR7 for one thousand seed weight. With regard to seed yield, the best hybrids with positive average heterosis were SA3 x SR41 (53.42%), SA4 x SR45 (52.75%), SA4 x SR1 (52.25%) and SA3 x SR10 (40.63%) which also combined with high seed yield of 1581 kg/ha, 1479 kg/ha, 1474 kg/ha, and 1457 kg/ha, respectively. These hybrids (involving the female line SA3 or SA4 and the male lines (SR10, SR13, SR41 and SR45) can be used in our breeding program in an attempt to develop local sunflower hybrid (s) with high seed yield and other important agronomic traits and for testing their yield potential and stability across locations and seasons.  أجريت هذه الدراسة بهدف تقدير التباين الوراثي و قوة الهجن  للإنتاجية ومكوناتها لأربعين هجين مفرد من محصول زهرة الشمس، نتجت من تهجين أربعة أمهات ذات عقم ذكرى سايتوبلازمى مع عشرة آباء معيدة للخصوبة. أجريت التجربة بمحطة بحوث سنار فى وسط السودان بالقطاع المروي لموسين             (صيف وشتاء2007). أستخدم تصميم القطاعات العشوائية الكاملة بثلاثة مكررات. كانت الصفات المدروسة هى عدد الايام حتى 50% إزهار، طول النبات، قطر القرص، عدد البذور بالقرص، وزن الآلف حبة، وانتاج البذور. أظهرت النتائج فروقات معنوية لكل الصفات في الموسمين مع تفوق الهجن وتباينها وراثياً مقارنة بالآباء. وفي التحليل المشترك لحساب قوة الهجين لكل الصفات كنسبة زيادة أو نقصان من متوسط الأبويين، ظهر أنّ الهــجينينSA2 x SR41  وSA3 x SR 41 هما الأفضل للإزهار والنضج المبكر، الهجين SA1 x SR14 لطول النبات، الهـجين SA2 x SR14 لقطر القرص ، الهجينين SA2 x SR13  و SA3 x SR13 لعدد البذور بالقرص، الهجين SA3 x SR7 لوزن الألف بذرة. أما بخصوص إنتاجية البذور أظهرت بعض الهجن نسبة قوة هجين موجبة SA3 x SR41 ) (53.42%، (52.73% ) SA4 x SR45،   SA4 x SR1   (52.25%)و SA3 x SR10 ((40.63% وإنتاجية بذور تقدر بـ 1581 كيلوجرام للهكتار، 1479 كيلوجرام للهكتار، 1474 كيلوجرام للهكتار و1459 كيلوجرام للهكتار علي التوالي. ويستنتج من هذه الدراسة ان الهجن التي يدخل في تركبيها الأم SA3 أو الأم SA4 مع الآباء SR41 ، SR45، SR13      و SR10 هى هجن متفوقة لإنتاجية البذور والصفات الأخرى ، ويمكن استخدام تلك الأمهات والآباء في تطوير هجن محلية مفردة من محصول الزهرة واختبار ثبات إنتاجيتها عبر المواسم والمواقع المختلفة

Assessment of Sudanese sunflower hybrids for yield, yield components and stability

Development of local sunflower hybrids with superior yields and stable across different environments is the main objective in our breeding program. For this purpose, ten local Sudanese sunflower hybrids designated as SFH32, SFH36, SFH37, SFH310, SFH313, SFH314, SFH341, SFH345, SFH302, and SFH325 were evaluated against Hysun-33 for yield potential and its components at Sennar, Wad Medani, Rahad, New Halfa and Suki. The experiment over all irrigated environments was laid out in RCBD with three replicates during the winter season of 2008. There was considerable variation for yield and its components among hybrids and locations. Genotype-environment interactions through different parameters and the performance of six traits of hybrids were studied. The six traits were plant height (cm), number of seeds per head, percentage of empty seeds,    100-seed weight (g),seed yield (kg ha-1) and oil yield (kg ha-1).Significant differences were observed for hybrids (G), locations (E) and G xE interaction for these six traits. Stability analysis after Eberhart and Russell’s model suggested that the hybrids used in this study were all, more or less, responsive to environmental changes. Most of the hybrids performed better in E4 (New Halfa). Stability analysis identified SFH37 and SFH310 as stable hybrids for plant height, SFH345 and SFH302 were identified as stable for number of seeds per head, whereas, Hysun-33, SFH310 and SFH341 were found stable for low percentage of empty seeds and heavy seed weight, respectively. Three hybrids; SFH310, SFH313 and SFH341 performed better than Hysun-33 and other hybrids across five environments and were considered as most stable hybrids for seed and oil yields. In contrast, hybrids such as SFH32 and SFH37 with regression coefficients greater than one were regarded as sensitive to environmental changes for seed and oil yields. The hybrid SFH310 was identified as stable hybrid for various yield components. The three promising local hybrids were released in June 2009 for commercial production and the local seed production of the hybrid SFH310 (Bohooth-1) was adopted by some seed producers in the country. تطوير هجن محلية من محصول زهرة الشمس ذات إنتاجية عالية وثابته  فى مختلف البيئات ، يعتبر من أهم أهداف برنامج التربية. أجريت هذه التجربة للتقييم عشرة هجن محلية بالرموز SFH32، SFH36 ، SFH37، SFH310، SFH313، SFH314، SFH341، SFH345، SFH3302، و25SFH3 واختبارها مع الشاهد Hysun-33 فى خمسة بيئات مروية هى سنار ، واد مدني، الرهد، حلفا الجديدة، والسوكي لمعرفة مقدرتها الإنتاجية الكامنة. أستخدم تصميم القطاعات العشوائية الكاملة بثلاثة مكررات لتنفيذ التجربة فى كل موقع خلال الموسم الشتوي 2008/2009. أوضحت النتائج وجود فروقات كبيرة فى الإنتاجية و مكوناتها بين الهجن والمواقع. كما أوضح تفاعل الطرز الوراثية مع البيئة ((genotype x environment interactions وجود فروقات معنوية عالية لسته صفات تمت دراستها وهى أطوال النباتات (سنتمترات) وعدد البذور بالقرص والنسبة المئوية للبذور الفارغة ووزن المائة بذرة (جرامات) وإنتاجية البذور(كيلوجرامات/هكتار) وإنتاجية الزيت (كيلوجرامات/هكتار).أوضح تحليل ثبات الإنتاجية  stability analysis بإســـــــتخدام نموذج Eberhart and Russell’s model بان جميع الهجن لها استجابات متباينة مع المتغيرات البيئية فى المواقع الخمسة وكان أفضل الأداء فى حلفا الجديدة (.(E4 كما أوضح التحليل بان الهجينين SFH37  و SFH310 هما من الهجن المستقرة و الثابتة الأداء لصفة أطوال النباتات و الهجينين SFH345  و SFH302 لصفة عدد البذور بالقرص ، بينما الهجن Hysun-33  ، SFH310، وSFH341 لصفتي النسبة المنخفضة من البذور الفارغة والوزن المرتفع للمائة بذرة علي التوالي. أوضحت الدراسة ان ثلاثة هجن محلية  (SFH310، SFH313 و SFH341) وخاصة الهجين SFH310 ، لها مقدرة إنتاجية عالية من البذور والزيت وثبات الإنتاجية فى البيئات الخمسة مقارنة مع الشاهد Hysun-33 وباقي الهجن ، بينما هجن اخرى مثل الهجينين SFH32  وSFH37  تعتبر حساسة للتغيرات البيئة فى إنتاجيتها من البذور والزيت. تم التعرف على الهجين SFH310 بأنه أكثر ثباتاً للإنتاجية ومكوناتها. الهجن السودانية الثلاثة الواعدة تمت إجازتها في يونيو 2009 للإنتاج التجاري والأنتاج المحلي لبذور الهجين SFH310 (بحوث-1= Bohooth-1) تم تبنيه من بعض منتجي البذور فى السودان. &nbsp