How is blood pressure measured?

A person's arterial blood pressures are usually measured with the help of an inflatable cuff wrapped around the upper arm at the level of heart. A stethoscope is used to monitor the sound of the blood flowing through an artery below the cuff. The cuff is first inflated until the flow of blood stops then the pressure of the cuff is gradually reduced until the blood just begins to flow, which is recognized by a gurgling sound in the stethoscope. This pressure, called systolic, represents the maximum pressure the heart produces in the artery. The pressure in the cuff is then further reduced until the gurgling stops, which corresponds to the restoration of normal blood flow. The pressure at this time, called diastolic, represents the pressure in the artery between the contractions of the heart.   

Physicians express blood pressures in torr, where 1 torr is the pressure exerted by a column of mercury 1 mm high; it is equivalent to 133Pa. The torr was formerly referred to as the "millimeter of mercury", abbreviated mm Hg. The unit is named after Evangelista Toricelli (1608-1647), the Italian Physicist who invented the barometer, which measures atmospheric pressure. Average atmospheric pressure is 760torr. In a healthy person the systolic and diastolic blood pressures are, respectively, about 120 and 80torr.   

How does particular metal crystallize to particular structure?

The reason for a particular metal to crystallize in a particular structure must be sought in the fact that the free energy E-TS for this system is lower than that for any other structure.

The same remark may be made with reference to those metals which have different structures in different temperature regions(Allotropy). This phenomenon is exhibited especially by three and four valent metals and by the transition metals.

For instance, Alpha Iron(BCC) is stable upto 910 deg.centigrade; between 910  and 1400 degree Centigrade the stable structure is gamma Iron(FCC); between 1400 and the melting point (1530) the structure is again BCC( Delta iron).

The transformation from one structure to another is dictated by the requirement of minimum free energy. This does not mean that such transformations takes place as soon as the existing structure becomes unstable.

In fact, a transformation of structure involves a rearrangement of atoms, and such a process may take a long time. The reason is that even though the free energy after the transformation is lower than in initial state, the two states are usually separated by an energy barrier or activation energy.

Thermodynamics specifies only the equilibrium condition but doesn't give any information about the velocity of reaction or processes involved in establishing equilibrium. From the atomic point of view, the stability of crystal structures is a problem of cohesive energy, involving the interaction between the atoms.