Differential Scanning Calorimetry (DSC)

The main application of DSC is in studying phase transitions, such as melting, glass transitions, or exothermic decompositions. These transitions involve energy changes or heat capacity changes that can be detected by DSC with great sensitivity. Differential scanning calorimetry or DSC is a thermo analytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference are measured as a function of temperature. Both the sample and reference are maintained at nearly the same temperature throughout the experiment. Generally, the temperature program for a DSC analysis is designed such that the sample holder temperature increases linearly as a function of time. The reference sample should have a well-defined heat capacity over the range of temperatures to be scanned. There are two types of DSC systems in common use. In power compensation DSC the temperatures of the sample and reference are controlled independently using separate, identical furnaces. The temperatures of the sample and reference are made identical by varying the power input to the two furnaces the energy required to do this is a measure of the enthalpy or heat capacity changes in the sample relative to the reference. In heat flux DSC, the sample and reference are connected by a low-resistance heat-flow path (a metal disc). The assembly is enclosed in a single furnace. Enthalpy or heat capacity changes in the sample cause a difference in its temperature relative to the reference; the resulting heat flow is small compared with that in differential thermal analysis (DTA) because the sample and reference are in good thermal contact. The temperature difference is recorded and related to enthalpy change in the sample using calibration experiments.

contoh surat minta kerja

22 JUN 2010
Mohd Halizi Bin Hassan
Blok 7-5, Perumahan Pantai Permai,
Jalan Pantai Permai,
59200 Kuala Lumpur

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Dear Sir,
RE: APPLICATION FOR MANAGER POSITION
I wish to apply for the position of manager position as advertised in mudah.my homepage on the 22st june 2010. I'm currently enrolled in the final year of a science physics course at the University Malaya, and will graduate in September 2010.

Your company's unique involvement and position in the business process has prompted me to apply for the manager position in your organization. I am very interested in pursuing a career in the area of administration. My academic transcript, which I have enclosed, shows that I have completed a wide range of subjects that provide me with a firm base of knowledge and skills relevant to the requirements of the editor service position.

My attached resume demonstrates my capacity to be a leader, who is able to work in a team environment, set and achieves long and short term goals, think analytically and solve problems. I believe my knowledge and technical know-how in the field of management will help me contribute a great deal to your company. Above all, I possess the interest and determination to perform well in the graduate position you are offering.

I look forward to meeting with you to discuss the position further. I can be contacted on 017- 401940 between the hours of 9 a.m. to 9 p.m., and the following e-mail address: halizi_87@yahoo.com
Thank you for your consideration.
Yours sincerely,
halizi
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(MOHD HALIZI BIN HASSAN)
Enclosed: Resume, Academic Results, References.

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STERN'S -GERLACH'S EXPERIMENT

STERN'S-GERLACH'S EXPERIMENT

The theory of spatial quantization of the spin moment of the momentum of electrons of atoms situated in the magnetic field needed to be proved experimentally. In 1920 (two years before the theoretical description of the spin was created) Otto Stern and Walter Gerlach observed it in the experiment they conducted.
The atoms of silver from the source which was the furnace with boiling silver were leaded to the vacuum space. There (thanks to the thin slides) the flat beam of those atoms was created. Then the beam got into non-homogeneous magnetic field and incidenced a photographic plate. Using classic physical laws we would expect the single picture of the beam on the plate. Whereas the beam of the atoms passing through not homogenous magnetic field undergoes splitting. That is why Otto Stern and Walter Gerlach received the two lines on the photographic plate.

The phenomena can be explained with the spatial quantization of the spin moment of momentum. In atoms the electrons are located in such way that in the each next pair of electrons there is one of the upward spin and one of the downward spin. So the whole spin of such pair is equal zero. But in the atom of silver on the outer shell there is a single electron which spin is not balanced by any electron.
The circulating causes some magnetic dipole moment (it's like it was a very small magnet). There is a force moment in the magnetic field influencing the dipole that is turning it until its position is the same as the direction of the field B. There is some other force influencing the dipole in the field. When the dipole is directed the same as the magnetic field then the dipole is pulled by that force in to the space of a strongest field. But if the dipole is directed opposite to the fields direction is pulled by that force out from the space of a strongest field.
So the atom of silver having one electron on the outer shell can be pulled in or out the space of a strongest magnetic field, what depends on the value of the magnetic spin quantum number. When the spin of the electron is equal +1/2 the atom is pulled out and when the spin is equal -1/2 the atom is pulled in. So during passing through the non-homogenous magnetic field the beam of the atoms of silver undergoes splitting into the two beams. Each of them consist of atoms which outer electrons are of the same spin.
In 1927 Phipps and Taylor conducted a similar experiment. This time they used atoms of hydrogen, not silver. They also observed that the beam of atoms undergoes splitting into two ones.
Later scientists conducted experiments using other atoms which have only one electron on the outer shell (cooper, gold, sodium, potassium). Every time there were two lines achieved on the photographic plate.
Of course in the atom not only electrons have spin. The elements of the nucleus also have it. But protons and neutrons are much more heavier than electrons (about 1836 times), and the magnetic dipole moment is inversely proportional to the mass. So the proton's and neutron's magnetic dipole momentum is much smaller than the one of the whole atom. This small magnetic dipole was later measured by Stern, Frisch and Easterman.