Friday, April 29, 2011

sem 4 dlm kenangan... solid state

arini mgkn last day of the this sem for those yang balik arini.. kpd mereka, selamat jalan diucapkan.. kalo xsilap, YB Dato' harun n eddy dila balik ari ni.. semoge mereke2 yg balik arini selamat sampai ke rumah masing safe n sound~~ hehee.. jumpe sem 5 nnt okei!

dlm boring layan lagu sedetik lebih, terjumpe plak project BEC-solid state. haha.. tersenyum sejenak ak~~ hahaaa.. byk kenangan mende ni.. mmg wajid di-treasure-kan ni!! hahaa...

oo bg mereke yg kurang mengerti ape tu BEC (Bose-Einsten Condensate) ni, hehee.. mai sini nk kasi explain sikit hehee~~

BEC ni salah satu state of matter. terjadi bile suhu terlalu sejuk yakni sgt2 menghampiri absolute zero. absolute zero ni suhu dlm Kelvin.. 0 kelvin = -273 celcius.

BEC ------> solid -> liquid -> gas ------> plasma
-->>>---------[suhu meningkat]---------------->>>

nk tau lebih? hahaa... boleh la bace jurnal pertama saya bg BEC ni.. (>_0)b
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close-up jurnal:

Matter can exist in various states. At high temperature, matter exist in the form of gas. If the matter in this form cools down, it becomes liquid. If the liquid form of matter cools down, it will becomes solid. These three states of matter were common to us. At extreme temperatures, the matter will exist in entirely different state of matter which not too commonly seen. For example at extremely high temperature the matters exist in the form of plasma while at extremely low temperature the matters exist in the state known as Bose-Einstein Condensate.
In 1924, Satyendra Nath Bose sent paper to Albert Einstein on quantum statistics of how light (photons) behave to hold atom. After realising the important of the concept, einstein did a further calculations which lead to a prediction that if matter was somehow cooled down to extreme low temperature just slightly above the absolute zero, the matter will formed a new and weird state of matter called the Bose-Einstein Condensate. This state of matter however was only a teory until seventy years later when an experiment about it was conducted by Eric Cornell and Carl Wieman. In the experiment, the first gaseous condensate was produces by cooling Rubidium atom to 170 nanoKelvin
Matters that exist in the form of Bose-Einstein Condensate known as Boson. Since boson does not follow the Pauli
exclusion principle, which electrons cannot occupy the same place, boson can overlap with one another forming one big collection of bosons. When this happen, each of the bosons will have the same wave function which tell us the definite probability of the uncertain location of the boson in space. In quantum mechanics point of view, we can say that each of the bosons are identical. Because of the overlapping of the bosons and also their wave function, the bosons lose their identities and become indistinguishable to one another.

Preparation of BEC
To prepare such bizarre condensate, boson need to be cooled down to extreme temperature approxiamately 170 nanoKelvin and the density is tremendously high.
To meet both conditions to prepare BECs, physicists often used techniques such as laser cooling, magnetic trapping and evaporative cooling. Alkali atoms like Lithium(Li), Sodium(Na) and Rubidium(Rb) were likely to be used because they can be very efficiently laser-cooled.
The first step to attain BECs is laser cooling. Laser cooling works by scattering photons from moving, which in this case, moving alkali atoms. Since the alkali atoms can absorb and emit photons many times, the tenperature of the atoms will be quickly reduced. This technique can reduced the atoms temperature down to 50 microKelvin with density of 5x1011 cm-3. However the temperature and density were not enough for BECs to appear. To solve this, both magnetic trapping and evaporative cooling were use by the physicists. The atoms in a free space will be trapped by the magnectic field that produced by a simple arrangements of electromagnets. Atoms that have high energy which above the depth of the trap will escape from the trap by evaporating. The escaping atoms are mostly among the hottest atoms in magnetic field traps. This means that there will be only cooler atoms left inside the trap and this temperature will slightly reduce time by time in a slow and steady rate. The effect of the temperature dropped also cause the atoms to sink deeper into the trap resulting an increasing in the number of density. In this case, both temperature and density will continuously decrease and increase respectively by mutual effects between themselves.


BECs in the future
In the near future, BECs might hold the key to some new branchs of physics and technologies.
The most promising BECs have to offer is etching. BECs are like laser when they in their coherence and fashioned into a beam. The beam of BECs would have greater energy and more presicion than a laser. This is because the massive particles of the BECs have more energetic than the massles photon of the laser.
The superfluidity is also one of the unic properties of BECs which can be very beneficial to us. BECs flow without any interior fricrion. To make it more interesting, BECs can slow down travelling light to a very unbelievable speed. This can possibly revolutionize the way we communicate with each others.




2 comments:

  1. wah,,bagus pandaeo nie~~tulis sal bec..ahahah

    ReplyDelete