A typical axial-flow gas turbine turbojet, the J85, sectioned for display

A gas turbine, also called a combustion turbine, is a rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. (Gas turbine may also refer to just the turbine element.)

Energy is added to the gas stream in the combustor, where air is mixed with fuel and ignited. Combustion increases the temperature, velocity and volume of the gas flow. This is directed through a nozzle over the turbine's blades, spinning the turbine and powering the compressor.

Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, generators, and even tanks.

History

150: Hero's Engine (aeolipile) - apparently Hero's steam engine was taken to be no more than a toy, and thus its full potential not realized for centuries.

1500:..............

Particle image velocimetry (PIV) is an optical method used to obtain instantaneous velocity measurements and related properties in fluids. The fluid is seeded with tracer particles which, for the purposes of PIV, are generally assumed to faithfully follow the flow dynamics. It is the motion of these seeding particles that is used to calculate velocity information of the flow being studied. Other techniques used to measure flows are Laser Doppler velocimetry and Hot-wire anemometry. The main difference between PIV and those techniques is that PIV produces two dimensional vector fields, while the other techniques measure the velocity at a point.

With PIV is generally considered cases where the particle concentration is such that it is possible to identify individual particles in an image, but not with certainty to track it between images. When the particle concentration is so low that it is possible to follow an individual particle it is called Particle tracking velocimetry, while Laser speckle velocimetry is used for cases where the particle concentration is so high that it is difficult to observe individual particles in an image.

History

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محبت‏بر دوگونه است : محبت صادق و محبت كاذب.  

محبت صادق آن است كه انسان كمال را درست تشخيص بدهد و البته وقتى به كمال آگاهى پيدا كند، به آن دل مى‏بندد مانند محبت‏به خداوند، متقابلا كمال هم جاذبه دارد و محب را به سمت‏خود جذب مى‏كند و در حقيقت محبت صادق، دو جانبه است; اما محبت كاذب آن است كه انسان، نقص را كمال بپندارد و بر اساس چنين پندار باطلى به آن كمال موهوم علاقمند گردد; مانند محبت غير خدا، مخصوصا محبت عالم طبيعت، محبت كاذب و جاذبه‏اى است كه عين دافعه است; چنانكه افعيها با نفس كشيدن، برخى از حشرات را جذب مى‏كنند; اما نه براى پرورش و كمال بلكه براى هضم و نابود كردن. بنابراين، جذب آنان، جذب كاذب است.

زرق و برق دنيا نيز چنين است. انسان اگر به دنيا دل ببندد، دنيا جاذبه دارد و او را به سوى خود جذب مى‏كند; اما براى اين كه او را درهم بكوبد و نابود و سپس به صورت زباله دفع كند، ولى ذات اقدس خداوند نه تنها محبوب مؤمنان است‏بلكه محب آنان نيز هست و آنان را به سمت‏خود جذب مى‏كند تا آنها را بپروراند و احيا كند. از اين رو، همان گونه كه گفته شده:

الا كل شى‏ء ما خلا الله باطل

و كل نعيم لا محالة زائل (1)

 در مورد محبت نيز بايد گفت هر محبتى غير از محبت‏خدا باطل و دروغين است.

 اميرالمؤمنين (عليه السلام) مى‏فرمايد:

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