Cool Days 
This page will give you a brief explanation of cryogenics. First, here are some definitions:
Cryotechnology: The application of the below sciences in technology
Cryogenics: the study of the production of cold temperatures
Cryophysics: the study of physical phenomena that occur at low temperatures
Cryoelectronics or Cryolectronics: the study of superconductivity
Cryotronics: the application of superconductivity
Condensed Matter Physics: the study of solid and liquid matter. This really isn't just cryophysics but a lot of condensed matter physicists end up studying cryoelectronics or quantum hydrodynamics
Cryobiology: the study of how living systems react to low temperatures
Cryonics: the study of freezing people in the hope of bringing them back to life after a cure for how they died has been discovered
Cryosurgery: surgery using cryogenics
Quantum Hydrodynamics: the study of superfluidity
Quantized Vortex Dynamics: The study of quantized vortices
Note: A common misconception that I have come across in my readings is that cryonics is often referred to as cryogenics or cryobiology. These are incorrect. Cryobiologists actually most of the time do not support cryonics at all.
Here is a timeline of important dates in cryogenics
1877- Liquid Oxygen is first produced
1908- Liquid Helium is first produced by Kamerlingh Onnes
1911- Superconductivity is discovered by Kamerlingh Onnes
1913- Nobel prize to Kamerlingh Onnes for liquefaction of helium
1933- Discovery of the Meissner- Oschenfield effect by Meissner and Oschenfield
1937- Superfluidity is discovered by Kapitza and Allen and Misener
1962- Nobel Prize to Landau for theories of condensed matter and liquid helium
1972- Nobel Prize to Bardeen, Cooper, and Schrieffer for the development of the BCS theory of superconductivity
1973- Nobel Prize to Josephson, Giaever for the prediction of the Josephson effect and tunneling in superconductors.
1978- Nobel Prize to Kapitza for discoveries in low temperature physics
1987- Nobel Prize to Bednorz and Muller for discovery of a new class of superconductors
1996- Nobel Prize to Lee, Osheroff, Richardson for discovery of superfluidity in 3He
2003- Nobel Prize to Ginzburg, Leggett, and Abrikosov for their work in superfluidity and superconductivity
Superfluidity is a discovery that has prompted many great physicists such as Landau, Kapitza, and Feynman to research properties of it. It was discovered in 1937 by Kapitza and Allen and Misener. Superfluidity is the property of liquid helium that makes it have zero viscosity so it will defy gravity and go up the side of a beaker without an external force. If you place the helium into a beaker and let it have an opening to go through and then you shine a light on it, it will form a fountain. This is called the fountain or thermomechanical effect.
The main interest in cryogenics is superconductivity. This is a phenomenon that allows certain metals known as superconductors to conduct electricity with zero resistance. A important test for superconductivity is the display of the Meissner-Oschenfield effect. This is the expulsion of magnetic fields from the interior of a superconductor. This effect is responsible for the levitation of a magnet above a superconductor. Many people have won Nobel Prizes for research into superconductivity such as Bardeen, Cooper, Schrieffer, Josephson, Giaever, Bednorz, Muller, Abrikosov, Leggett, and Ginzburg.
One cooling technique that was used intensively by Lee, Osheroff, and Richardson when they were working on the phase transitions in 3He but has giving way to more effective ways of cooling items down is the Pomeranchuk effect. This was proposed by Isaak Pomeranchuk a well known particle physicist but was not used until many years later. The effect states that as pressure is added to liquid 3He without heat flow then the helium will get colder as it solidifies. The Pomeranchuk cooling effect takes place in special cooling systems known as Pomeranchuk cells. The first successful Pomeranchuk cell was made by Anufriev and consisted of a diaphragm that is inflated with the other isotope of helium. The 3He is on the outside of this diaphragm and is pushed by the inflating diaphragm which then cools the helium.
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