la supraconductivité

[Nader 3:16]

la supraconductivité fut découverte en 1911 par le physicien H.onnes qui remarqua que le mercure refroidi a la temperature 4,2 K perdra toute résistance au passage du courant électrique. beaucoup de metaux possede cette proprietes.......
La supraconductivité est un phénomene manifeste par de matériaux qui n'opposent aucune resistance au passage d'un courant électrique, au dessous d'une temperature critique designée par Tc.
le passage d'un courant électrique a travers un corps conducteur (un metal) est du a la circulation d'un ensemble d'électrons a travers ce corps, sous l'effet d'un champ électrique.
Normalement, des interactions entre les électrons mobiles, qui sont résponsables de passage du courant et le reste de la matiere du corps conducteur constituent des obstacles a la circulation des électrons. Ceci est a l'origine de la résistance électrique du conducteur et de la perte d'energie par l'effet joule lors de la passage d'un courant.
dans un materiau supraconducteur, les électrons ne rencontrent pas d'obstacle au cours de leur circulation. ces materiaux ne possedent pas de résistance electrique et il n'y a pas de perte d'energie lors du passage de courant a travers eux .....

[Nader 3:16]

الموضوع نقلته من احد الكتب....و ما بعرف اذا هذه الخاصية عم تطبق لأنّو المشكلة انو لازم الحرارة تكون واطية جداً لحتا المعدن يتحول الى supraconducteur ...يعني كل ما كانت ال Tc قريبة من الصفر كل ما كان احسن...بس مش عارف شو هي اعلى Tc واصلين لها حتى الآن......

هذه لمحة عامة عن فكرة ال supraconductivite .....يعني لم ادخل بالتفاصيل ابداً...نتركها لخبراء آل الفلو لأنو الموضوع فيزيائي:)

[روعة]

هي فعلاً مستعملة
على سبيل المثال: هناك جهاز طبي الIRM (imagerie par resonnace magnetique) تحتاج إلى تيار عالي جداً للحصول على حقل مغناطيسي كبيييييييير لذا فهم يستعملون ال supraconducteur وللحصول على ال zero K فهم يستعملون ال helium gazeux بسبب حرارته الملائمة

[الزاهر]

ملاحظة صغيرة على كلامك في المشاركة 2 أخي نادر....أعلى Tc واصلنها عالية أد ما بدك وأكتر...لكن كل العمل يوصلو لأوطى Tc.....هون كنا عم نحكي عن 4 k هادي حرارة جد واطية......لكن لحد علمي.....تم الوصول إلى 0.6 K .....حسب الدكتور فؤاد الدرزي (Prof en Physique de semiconducteures اللي بيعلمني بالجامعة)>>رح شوف شو فيني ضيف على الموضوع بالمشاركة القادمة.......
سلامات

[الزاهر]

بعض اللي أحسست منه الغرابة فيم قرأت في الموضوع


Superconductors are also able to maintain a current with no applied voltage whatsoever, a property exploited in superconducting electromagnets such as those found in MRI machines. Experiments have demonstrated that currents in superconducting coils can persist for years without any measurable degradation. Experimental evidence points to a current lifetime of at least 100,000 years, and theoretical estimates for the lifetime of a persistent current exceed the lifetime of the universe


أوووووووووووووووووووووبس.....سماع هالحكي لنشوف!!!!


the highest critical temperature found for a conventional superconductor is 39 K for magnesium diboride (MgB2 superconductors can have much higher critical temperatures: ), although this material displays enough exotic properties that there is doubt about classifying it as a "conventional" superconductor. CuprateYBa2Cu3O7, one of the first cuprate superconductors to be discovered, has a critical temperature of 92 K, and mercury-based cuprates have been found with critical temperatures in excess of 130 K. The explanation for these high critical temperatures remains unknown



هلأ صحيح ما كتير فهمت أيشودا...لأن ما أيبلت.....بس حدا يشرحلنا.....


http://upload.wikimedia.org/wikipedia/en/thumb/1/17/Meissner_effect.jpg/800px-Meissner_effect.jpg




"In the late 1980s, Pacific Northwest National Laboratory researchers conducted research into superconductors. The ceramic superconductors are made from a material that has only very low alternating-current resistance and thus dissipates less power. Magnetic forces between the magnet and ceramic superconductor provide a magnetic cushion that keeps the magnet suspended above the superconductor. Liquid nitrogen cools the superconductor to about 77 Kelvin, producing the magnetic cushion
."

سماع لنشوف.....هههههههههه
حاصرين راسن منيح بالموضوع.........هههههههه



The question of how superconductivity arises in high-temperature superconductors is one of the major unsolved problems of theoretical condensed matter physics as of 2007. The mechanism that causes the electrons in these crystals to form pairs is not known.
Despite intensive research and many promising leads, an explanation has so far eluded scientists. One reason for this is that the materials in question are generally very complex, multi-layered crystals (for example, BSCCO), making theoretical modeling difficult. However, with the rapid rate of new discoveries in the field, many researchers are optimistic that a complete understanding of the process is possible within the next decade or so.

http://upload.wikimedia.org/wikipedia/commons/7/75/BI2223-piece3_001.jpg

A small sample of the high-temperature superconductor BSCCO-2223. The two lines in the background are 1 mm apart



بمناسبة الحديث عن The Absolute zero......طلع الدكتور الدرزي Outdated.......ههههههههههه
سماع لنشوف يا زعيم


Achieving record temperatures near absolute zero




It can be shown from the laws of thermodynamics that absolute zero can never be achieved artificially, though it is possible to reach temperatures close to it through the use of cryocoolers. This is the same principle that ensures no machine can be 100% efficient.

يحرأ أخت التيرمو شو.......

At very low temperatures in the vicinity of absolute zero,
matter exhibits many unusual properties including superconductivity, superfluidity, and Bose-Einstein condensation.

سامع......هلأ صار بدنا بحث عن الـ Superfluidity......المرة الجاية ....ههههههههههه


In order to study such phenomena, scientists have worked to obtain ever lower temperatures.
In September 2003, MIT announced a record cold temperature of 450 pK, or 4.5 × 10-10 K in a Bose-Einstein condensate of sodium atoms. This was performed by Wolfgang Ketterle and colleagues at MIT.[4]
As of February 2003, the Boomerang Nebula, with a temperature of –272.15 degrees Celsius; 1 K, is the coldest place known outside a laboratory. The nebula is 5000 light-years from Earth

هههههههههههههههه.......ليك لوين راحو

and is in the constellation Centaurus.
As of November 2000, nuclear spin temperatures below 100 pK were reported for an experiment at the Helsinki University of Technology's Low Temperature Lab. However, this was the temperature of one particular degree of freedom — a quantum property called nuclear spin — not the overall average thermodynamic temperature for all possible degrees of freedom.
In 1994, researchers at NIST achieved a then record cold temperature of 700 nK (billionths of a kelvin
ليك بأيش بيحصرو راسهم يا زلمة.......لعتــــــــــــــــــــــــا......ههههه ههه

[Nader 3:16]

شكراً لك يا اخ زاهر عالمعلومات....
بس يا ريت كنت كاتبها بالفرنسي كان افضل...

و ما تآخذنا على الرد المتأخر....لأنو مشغول بالجامعة...

و شكر لكل من شارك بالموضوع:rolleyes: