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عرض المشاركات من فبراير 26, 2015

الادارة الاحترافية

Why Do Birds Sing So Early in the Morning?لماذا تغرد الطيور عند الفجر؟!

صورة
Why Do Birds Sing So Early in the Morning? You head to work early; it’s still dark and cold. It’s too dark and cold to make a logical reason to be up, and already you can hear them – those crazy birds aren’t just awake, they’re already whooping it up with their trills, melodies and crescendos. You are witnessing what is often called the “dawn chorus” – that period of time before the sun shows itself, but when the great outdoors is already filled with beautiful sounds of nature. The birds that you hear are mainly males, doing what male birds do best, protecting/claiming their territory and/or trying to attract a mate. There are a few theories about why birds sing so vigorously during those per-light hours. For many years, the prevailing theory was that those early hours are typically the coolest and driest hours of the day and this lack of atmospheric variables allowed bird songs to travel the farthest, giving their voices better range, sending a message to other males that they...

Why is helium used in diving tanks? لماذا يتنفس غطاس البحار خليطا من الهيليوم والأكسجين؟

Air, which was first used in diving tanks, contains roughly 20% oxygen, and 80% nitrogen. The trouble with nitrogen in this situation is that nitrogen is a fairly heavy gas, and is soluble in blood at high pressure. Long term use of nitrogen can cause a strange sense of euphoria, or well being called nitrogen narcosis. This is a bit like being drunk, and makes the diver unable to assess dangers. Just as working drunk on the surface is not a good idea, working drunk at the bottom of the sea can be extremely hazardous. Divers working at depth would have nitrogen dissolved into their blood, and it becomes necessary to decompress (surface) very slowly, to allow the nitrogen to come back out of the blood to be breathed out. Divers who come up too quickly have a huge RISK of the nitrogen being released from the blood too quickly and forming bubbles in the bloodstream. This causes blockages, as the bubbles, although tiny, cannot pass through the fine capillaries. The condition is called ...

استعن بالانترنت و تعلم بذاتك ووفر نقودك واجعل القراءة مفتاحك (بدر الحوسني)

صورة

Why Spider is not located in conceding own ? لماذا لا يقع العنكبوت في شباكه الخاصة ؟

صورة
Why Spider is not located in conceding own ?? To answer this question, we must examine first miracle Cobweb Engineering. On the one hand the strength of silk yarn is the wisps that are stronger than steel fabric, not only quartz higher melt strength, and expands the string to five times its length before it stops. In fact, this little thread that appears to the naked eye is made the same way that makes the coal cable, where consists of several strands infinitesimal wrapped around each other, has a thickness of one thread, including (1) of the million of an inch. The materials made very common, where in one hectare of a British provinces, for example, more than two and a quarter of a spider. Each spider private spindles, usually numbering as many as three. This is a natural flirt found the lower abdomen. There are near each spindle small gland openings graduated article that are silk thread, a substance formed in the glands of the spider. During tissue engineering, the spider coll...

لماذا يتجنب المهندسون استخدام قلم الرصاص لوضع علامات على المعادن؟

صورة
لماذا يتجنب المهندسون استخدام قلم الرصاص لوضع علامات على المعادن؟ تتفاعل المعادن كهربائيا مع بعضها البعض ، بحيث تبدأ سلسلة من التفاعلات . وكما يحدث في المعادن فإن بعض المواد غير المعدنية تتمتع بخواص كهربائية وتشترك في التفاعلات . والكربون هو أحد هذه المواد ويندرج في لائحة المواد المتفاعلة ويلي القصدير تماما . ولا يقتصر الأمر على ذلك ، بل إن جميع المعادن تفقد الإلكترونيات أثناء هذه التفاعلات وهذا شيء مشترك بينها ، بينما الكربون يكتسب الإلكترونيات عندما يتفاعل مع بقية المعادن . هذا يعني أن تفاعله الكهربائي قوي جدا ومصدر طاقة جيد ، .  يتكون الرصاص في قلم الرصاص العادي من الغرافيت ( وهو نوع من الكربون ) والطين الصيني ( سيليكات الألمنيوم ). وكلما زادت قساوة القلم كلما زادت فيه نسبة الغرافيت. ولابد من تجنب  عمل  علامات أو الكتابة في معدن نشيط مثل الألمنيوم ، الذي قد يستخدم بشكل غير مدهون في  جناح الطائرة مثلا  ، قد يتسبب بكارثة اشتعال النيران بالطائرة بسبب تفاعل الكربون مع الالمنيوم . ولتفادي مثل هذه المشكلة  ، يجب على المهندس استخدام أداة حادة لوضع الإشا...

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