In this paper a hybrid energy system combining variable speed wind turbine, solar photovoltaic and fuel cell generation systems is presented to supply continuous power to residential power applications as stand-alone loads. The wind and photovoltaic systems are used as main energy sources while the fuel cell is used as secondary or back-up energy source. Three individual dc–dc boost converters are used to control the power flow to the load. A simple and cost effective control with dc–dc converters is used for maximum power ...

, a view to evaluate the fracture energy of concrete and to study the fracture and localization process, it is described herein this study an experimental investigation. Fracture energy for the early ages of concrete is estimated experimentally considering the weather of Kingdome of Saudi Arabia. Several experiment specimens of different ages, sizes, lengths and end head specimens are prepared and assessed. The specimens in early age are tested out to calculate the fracture energy of concrete using a direct tension test, taking into consideration the loss of energy due to the frictional process in the mechanism of experimental set up. Also the crack localization is considered during the experiment, as dealing with the localized fracture. In this experiment work, the measurements reach to the post peak softening branch of concrete using the direct tension.

ركز هذا البحث على مصادر الضوضاء داخل الوحدة السكنية نظرا لسهولة السيطرة على أغلبها دون الحاجة الى وسائل فنية معقدة أو مكلفة. ومن خلال البحث قيست مستويات الضوضاء التى تصدرها معظم الأجهزة المنزلية والتى ينتج عنها إزعاجاً واضحاً داخل الفراغ وقد تم تجاهل الأجهزة الكهربية التى وجد أن تأثيرها ضعيف، وتم قياس هذه الضوضاء عند الترددات المختلفة. كما تم قياس تأثير عناصر الفرش الموجودة فى الفراغات السكنية من ستائر وسجاد على مستوى الضوضاء داخل الفراغ. ومن خلال هذه القياسات حددت المصادر الأكثر إزعاجا كما حددت خصائص الضوضاء التى تنتج عنها. وإقترح البحث عددا من الحلول لتخفيض تأثير ضوضاء هذه المصادر على مستخدمى الوحدة السكنية معتمدا على النتائج التى توصل إليها البحث مع مراعاة ملائمة هذه المقترحات للواقع المحلى فى المدن المصرية من الناحية الإقتصادية أو التقنية أو الجمالية.

In this paper autonomous and nonautonomous modified hyperchaotic complex L¨ usystemsare proposed. Our systems have been generated by using state feedback and complex periodic forcing. The basic properties of these systems are studied. Parameters range for hyperchaotic attractors to exist are calculated. These systems have very rich dynamics in a wide range of parameters. The analytical results are tested numerically and excellent agreement is found. A circuit diagram is designed for one of these hyperchaotic complex systems and simulated using Matlab/Simulink to verify the hyperchaotic behavior.

In this paper autonomous and nonautonomous modified hyperchaotic complex L¨ usystemsare proposed. Our systems have been generated by using state feedback and complex periodic forcing. The basic properties of these systems are studied. Parameters range for hyperchaotic attractors to exist are calculated. These systems have very rich dynamics in a wide range of parameters. The analytical results are tested numerically and excellent agreement is found. A circuit diagram is designed for one of these hyperchaotic complex systems and simulated using Matlab/Simulink to verify the hyperchaotic behavior.

We study rheotaxis of bull sperm inside microchannels to characterize the effects of flow and wall shape on sperm swimming behavior. We found that large percentage, 80 to 84%, of sperm cells exhibited positive rheotaxis (sperm cells swimming against the flow) within flow velocities of 33 to 134 µm/s. Sperm cells were also found to reverse their swimming direction when liquid flow direction was reversed. Time taken by sperm cells to reverse their swimming direction was inversely proportional to flow velocity. Sperm behavior was significantly affected by sperm position with respect to channel wall. Sperm cells close to channel wall moved upstream faster than sperm cells moving along channel centerline. Shear stress, which is an indicator of velocity distribution, was found to play an important role in regulating rheotactic behavior of sperm cells. Side pockets were added to some microchannels to mimic storage sites in mucosal folds and pockets in the fallopian tube of female reproductive system and sperm interaction with these pockets was monitored. We found that sperm cells tend to follow channel walls and enter these pockets without any chemical binding, which further confirms the wall tracking behavior of mammalian sperm cells. Our results confirm that sperm rheotaxis is a strong mechanism for guiding sperm cells to the oocyte along the female genital tracts.