Complex Centers of Polynomial Differential Equations

We present some results on the existence and nonexistence of centers for polynomial first order ordinary differential equations with complex coefficients. In particular, we show that binomial differential equations without linear terms do not complex centers. Classes of polynomial differential equations, with more than two terms, are presented that do not have complex centers. We also study the relation between complex centers and the Pugh problem. An algorithm is described to solve the Pugh problem for equations without complex centers. The method of proof involves phase plane analysis of the polar equations an a local study of periodic solutions.Comment: 18 page

Studying of the optical properties of poly (vinyl alcohol) films using Aluminum sulphate as additive by measuring allowed direct transition energy gap

The change in the optical band gap and optical activation energy have been investigated for pure Poly (vinyl alcohol)and Poly (vinyl alcohol) doped with Aluminum sulphate to proper films from their optical absorption spectra. The absorption spectra were measured in the wave range from (200-700) nm at temperature range (25-140) 0C. The optical band gap (Eg) for allowed direct transition decrease with increase the concentration of Aluminum sulphate. The optical activation energy for allowed direct transition band gap was evaluated using Urbach- edges method. It was found that ?E increases with increasing the concentration of Al2 (SO4)3 and decreases when temperature increases

Analysis and design of linear induction machines

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The Green Synthesize of Zinc Oxide Catalyst Using Pomegranate Peels Extract for the Photocatalytic Degradation of Methylene Blue Dye

تهدف الدراسة الى تحضير جسيمات أوكسيد الزنك باستخدام مستخلص قشر الرمان الذي بدوره يتفاعل مع ملح خلات الزنك بوجود هيدروكسيد الصوديوم كعامل مرسب. تم توصيف الجسيمات النانوية المركبة من خلال جهاز مطيافية الانعكاس المنتشر بالاشعه المرئية وفوق البنفسجية UV-VIS diffuse reflectance Spectroscopy  ، والتحليل الطيفي بالأشعة تحت الحمراء بجهاز (FTIR) ، بينما تم دراسة تضاريس سطح العامل المساعد باستخدام مجهر القوة الذرية   AFM   اثبتت نتائج التشخيص باستخدام المطياف وجود العديد من المجموعات الفعالة النشطة لمستخلص قشر الرمان الذي يعتبر بيئة مثالية للترابط مع ملح خلات الزنك لإنتاج جسيمات أوكسيد الزنك النانوية.  فيما اثبتت نتائج جهاز مطيافية الانعكاس المنتشر بالاشعه المرئية وفوق البنفسجية انه تم تسجيل ازاحة نحو الطول الموجي القصير لاوكسيد الزنك المحضر باضافة مستخلص قشر الرمان وبفارق ازاحة 8 نانوميتر مقارنة مع أوكسيد الزنك  المحضر من دون اضافة مستخلص قشر الرمان.  يرجع أصل هذه الازاحة نحو الطول الموجي القصير  إلى تأثير الحجم الكمي. تم التحقق من كفاءة إزالة الصبغة الزرقاء باستخدام جسيمات أوكسيد الزنك  النانويه المحضره بأضافة / بدون اضافة مستخلص قشر الرمان بوجود اشعة الشمس كمصدر للطاقة وكان النشاط التحفيزي عاليًا لكلا المحفزين وبواقع كفاءه 88% بعد مرور 60 دقيقه من التفاعل تحت اشعة الشمس.In this study, the zinc oxide NPs have been synthesized from the fresh pomegranate peels extract using the precipitation method. The ZnO nanoparticles were produced from the reaction of fresh peels extract with zinc acetate salt which was used as zinc source in the presence of 2 M NaOH. The green synthesized nanoparticles were characterized through X-ray diffraction (XRD), UV-Vis diffuse reflection spectroscopy, Fourier transform infrared spectroscopy (FTIR), and Atomic force microscopy (AFM). The XRD patterns confirm the formation of hexagonal wurtzite phase structure for ZnO synthesized using pomegranate peels extract with average crystalline size of 28 nm. FTIR spectra identify the presence of many active functional groups for the pomegranate extract which is ideal to bind with zinc acetate to produce the ZnO nanoparticles during the preparation method. The reflection spectra of green synthesis ZnO with pomegranate extract observed a blue shift towards lower wavelength with (8 nm) difference compared to ZnO without the addition of any extract.  The provenance of such blue shift towards shorter wave length was due to the quantum size effect. The Atomic force microscopic (AFM) result shows average roughness value for ZnO nanoparticles of 6.26 nm. The decolorization efficiency of the methylene blue dye was investigated using the ZnO nanoparticles under sun light irradiation and it was compared with the bare ZnO synthesized without the addition of extract. The catalytic activity was about 88% after 60 min of sunlight irradiation for both prepared catalyst however, the decolorization efficiency of ZnO with the addition of extract was higher at the first 16 min compared to bare ZnO

A Review of Control Techniques Future Trends in Wind Energy Turbine Systems with Doubly Fed Induction Generators (DFIG)

تعتبر طاقة الرياح حاليا واحدة من أكثر مصادر الطاقة الخضراء النظيفة الملاءمة على نطاق واسع في العالم. تم تطوير العديد من مبادئ توربينات الرياح بستخدام  المولدات المختلفة لتحويل طاقة الرياح المتاحة إلى طاقة كهربائية. يعد نظام المولد الحثي ذي التغذية المزدوجة DFIG لتوربينات الرياح ذات السرعة المتغيرة نسبيا (VSWT) هو الأكثر ملاءمة لطاقة توربينات الرياح بسبب فوائده العديدة مقارنة بتوربينات الرياح ذات السرعة الثابتة نسبيا (FSWT). تقدم هذه الورقة مراجعة و مقارنة عن طاقة توربينات الرياح المختلفة وملخصًا قيمًا للعمل الأخير المتعلقة بأنظمة طاقة الرياح المختلفة (WECS) لنمذجة DFIG وأقصى نقطة طاقة MPP وأحدث نظام تحكم للتشغيل. ومن ناحية أخرى تم في الدراسة الحالية تقديم مقارنات ومناقشات بين توربينات الرياح المختلفة لتكون مفيدة للدراسات البحثية.Wind energy is currently widely regarded as one of the most favorable green clean sources of energy. Several wind turbine principles with various generator architectures have been evolved to exchange the available wind energy into electric power. The DFIG partial Variable-Speed Wind Turbine (VSWT) system is most proper for wind turbine energy because of its numerous benefits over Fixed-Speed Wind Turbines (FSWT). This paper introduces a comparative review of the different wind turbine conversion energy and a valuable summary of the recent work in the literature on different Wind Energy Conversion Systems (WECS) of a DFIG modeling, Maximum Power Point (MPP), and the latest control system for operation. On the other side, comparisons and discussions between different wind turbines have been presented in the current study to be beneficial for research studies

The poet ‘Umāra al-Yamanl

Abū Muḥammad ‘Umarā ibn ‘Alī was born in the Yemen in 515/1121. He studied jurisprudence at Zabid (531-535 A.H.) then he taught Shāfi ‘ī Jurisprudence there. While on pilgrimage to Mecca in 538/1145 he met the Queen al-Ḥurra of Zabid and became one of her close friends. He began trading between Aden and Zabid in 538 A.H., and became rich, famous, and a friend of Ibn Saba’ (the Dā’ī of Aden), his Vizier Bilāl b. Jarīr and his secretary al-‘Abdī. He was sent by the Prince of “al-Haramain” (Qāsim b. Hāshim b. Falita), on a mission to the Fatimid Caliph (al-Fā’iz) in Egypt in 549 A.H. So successful was his mission that the Prince of al-Ḥaramain sent him on another mission in 551 A.H. He went to Egypt and settled there, living happily until Saladin ended the Fatimid Callphate in 567 A.H. when ‘Umāra was involved in a plot to replace the son of the last Fatimid Caliph on the throne. The plot was betrayed and ‘Umāra was executed on 2 Ramaḍān 569/6 April 1175) (Chapter 1 Part I P. 28-78). 2. ‘Umāra had a good character, so that most people liked and respected him. He was a faithful and pious Moslim, so that he seemed proud of his religion. He belonged to Shāfi’ī sect by birth, education and in his way of thinking; so it was said that he was a fanatic of sunna,. He was one of the most learned of the people of his time. He studied jurisprudence, Tafsīr, Hadith, Ḥistory, Arabic literature and language. Then he wrote many books in addition to his “Dīwān”: al-Nukat al-‘Aşriyya, Tārikh al-Yaman, Shu‘arā’ al-Yaman, al-Farā’iḍ and Sīrat al-Sayyida Nafīsa. All this made him gain a good position in society (Chapter 2 P. 77-129). 3. ‘Umāra’s poetic talent was revealed in Adon by the help of al-‘Abdī, grew at Zabid, and his fame made complete in Egypt especially when he joined “Dīwān al-Shu’arā’” in the Fatimid Caliphate. So he became one of the greatest poets of his time until Saladin’s reign when he become neglected. (Chapter 1 Part II P. 131-159). 4. ‘Umāra was a panegyrist. He was expert in eulogy in which was most of his poetry, but he also wrote in most of the poetical themes common to this time; elegy opistolary-poetry, satire, love poetry, ascetic-poetry, descriptive-poetry and other themes. (Chapter 2 P. 160-230). 5. ‘Umāra constantly sought to express his ideas lucidly, so most of his poetry was understood by ordinary readers. Although his style was not distinguished, it was adequate, and his language was eloquent. He was fond of rhetorical figures (Badī’) which can be seen in most of his poetry. While he avoided strange rhymes and rare metres he wrote many "Urjāzas" and "Muwashshaḥs". (Chapter 3. P. 23I - 282). 6. ‘Umāra made use of some of his predecessors’ art, especially Abū Tammām, al-Buḥturi and al-Mutanabbī. Similarly some of his followers benefitted from his art. His poetic thought and descriptions reached a high level, and he won the admiration of Arabs everywhere. His importance, then, was as a poet who was able to recording his poetry the events which happened in his time, and he was one of the pioneers of "Muwashshaḥs" in the east. (Chapter 4. P. 283 - 318)

The behavior of tapered one-way continuous two-span reinforced concrete slabs under repeated load

The scope of this study is to look at the effect of supplying a non-prismatic cross-section on the flexural strength of one-way continuous slabs reinforced concrete (RC) with two spans under repeated load. The research aims to study the ability of non-prismatic slabs to increase flexural stiffness which leads to saving construction costs. For this purpose, experimental investigations were carried out; the work consisted of fabrication and testing six two-span RC slabs with the same volume of concrete. Two of them were prismatic with a constant depth, while all the others were non-prismatic with tapered cross-sections having varying depth. Prismatic slabs were stiffer than non-prismatic slabs in all support settings, according to the findings. It is found that providing a tapered slab with a positive or a negative haunch has an insignificant effect on the bearing capacity for a prismatic slab. On the other hand, the tapered slab led to increase the deflection at service load compared to the prismatic slab

Excitation sources for structural health monitoring of bridges

Vibration-based damage detection (VBDD) methods are structural health monitoring techniques that utilize changes to the dynamic characteristics of a structure (i.e. its natural frequencies, mode shapes, and damping properties) as indicators of damage. While conceptually simple, considerable research is still required before VBDD methods can be applied reliably to complex structures such as bridges. VBDD methods require reliable estimates of modal parameters (notably natural frequencies and mode shapes) in order to assess changes in the condition of a structure. This thesis presents the results of experimental and numerical studies investigating a number of issues related to the potential use of VBDD techniques in the structural health monitoring of bridges, the primary issue being the influence of the excitation source. Two bridges were investigated as part of this study. One is located on Provincial Highway No. 9 over the Red Deer River south of Hudson Bay, Saskatchewan. The other is located near the Town of Broadview, Saskatchewan, off Trans-Canada Highway No. 1, 150 km east of the City of Regina. Field tests and numerical simulations were conducted using different types of excitation to evaluate the quality of the modal properties (natural frequencies and mode shapes) calculated using these excitation types, and thus to evaluate the performance of VBDD techniques implemented using the resulting modal data. Field tests were conducted using different sources of dynamic excitation: ambient, traffic excitation, and impact excitation. The purpose of field testing was to study the characteristics and repeatability of the modal parameters derived using the different types of dynamic excitation, and to acquire data that could be used to update a FE model for further numerical simulation. A FE model of the Red Deer River bridge, calibrated to match the field measured dynamic properties, was subjected to different types of numerically simulated dynamic excitation with different noise (random variations) levels added to them. The types of dynamic excitation considered included harmonic forced excitation, random forced excitation and the subsequent free vibration decay, impact excitation, and different models of truck excitation. The bridge model was subjected to four different damage scenarios; in addition, six VBDD methods were implemented to evaluate their ability to identify and localize damage. The effects of uncertainty in the definition of controlled-force excitation sources and variation in measurement of the bridge response were also investigated. Field tests on the Hudson Bay bridge showed that excitation induced by large trucks generally produced more reliable data than that of smaller vehicles due to higher signal-to-noise ratios in the measured response. It was also found that considering only the free vibration phase of the response after the vehicle left the bridge gave more reliable data. Impact excitation implemented the on Hudson Bay bridge using a spring-hammer yielded repeatable and high quality results, while using a heavy weight delectometer for impact excitation on the Broadview bridge produced results of lesser quality due to the occurrence of multiple strikes of the impact hammer. In general, wind induced vibration measurements taken from both bridges were less effective for defining modal properties than large vehicle loading or impact excitation. All of the VBDD methods examined in this study could detect damage if the comparison was made between modal parameters acquired by eigenvalue analyses of two FE models of the bridge, before and after damage. However, the performance of VBDD methods declined when the dynamic properties were calculated from response time histories and noise was introduced. In general, the damage index method performed better than other damage detection methods considered. Numerical simulation results showed that harmonic excitation, impact excitation, and the free decay phase after random excitation yielded results that were consistent enough to be used for the identification of damage. The reliability of VBDD methods in detecting damage dropped once noise was introduced. Noise superimposed on the excitation force had little effect on the estimated modal properties and the performance of VBDD methods. On the other hand, noise superimposed on the “measured” dynamic response had a pronounced negative influence on the performance of the VBDD methods

Polynomial Differential Equations with Small coefficients

Classes of polynomial differential equations of degree n are considered. An explicit upper bound on the size of the coefficients are given which implies that each equation in the class has exactly n complex periodic solutions. In most of the classes the upper bound can be improved when we consider real periodic solutions. We present a proof to a recent conjecture on the number of periodic solutions. The results are used to give upper bounds for the number of limit cycles of polynomial two-dimensional systems.Comment: 15 page