<unk>  is a well-known rule for the physical adsorption of gas molecules on a solid surface, that is basis for an important analysis technique for the measurement of the specific surface area of a material.  In 1938, Stephen Brunauer, Paul Hugh Emmett, and Edward Teller published an article about the<unk>  in a journal for the first time; “BET” consists of the first initials of their family names.
The concept of the<unk>  is an extension of the Langmuir<unk> , which is a<unk>  for monolayer molecular adsorption, to multilayer adsorption with the following hypotheses: (a) gas molecules physically adsorb on a solid in layers infinitely; (b) there is no interaction<unk> ween each adsorption layer; and (c) the Langmuir<unk>  can be applied to each layer.  The resulting<unk>  equation is expressed by (1):
P
{\displaystyle P}
 and 
P
0
{\displaystyle P_{0}}
 are the equilibrium and the saturation pressure of adsorbates at the temperature of adsorption, 
v
{\displaystyle v}
 is the adsorbed gas quantity (for example, in volume units), and 
v
m
{\displaystyle v_{m}}
 is the monolayer adsorbed gas quantity. 
c
{\displaystyle c}
 is the<unk>  constant, which is expressed by (2):
E
1
{\displaystyle E_{1}}
 is the heat of adsorption for the first layer, and 
E
L
{\displaystyle E_{L}}
 is that for the second and higher layers and is equal to the heat of liquefaction.
Equation (1) is an adsorption isotherm and can be plotted as a straight line with 
1
/
v
[
(
P
0
/
P
)
−
1
]
{\displaystyle {1}/{v[({P_{0}}/{P})-1]}}
 on the y-axis and 
ϕ
=
P
/
P
0
{\displaystyle \phi ={P}/{P_{0}}}
 on the x-axis according to experimental results.  This plot is called a<unk>  plot.  The linear relationship of this equation is maintained only in the range of 
0.05
<
P
/
P
0
<
0.35
{\displaystyle 0.05<{P}/{P_{0}}<0.35}
.  The value of the slope 
A
{\displaystyle A}
 and the y-intercept 
I
{\displaystyle I}
 of the line are used to calculate the monolayer adsorbed gas quantity 
v
m
{\displaystyle v_{m}}
 and the<unk>  constant 
c
{\displaystyle c}
. The following equations can be used:
The<unk>  method is widely used in surface science for the calculation of surface areas of solids by physical adsorption of gas molecules.  A total surface area 
S
t
o
t
a
l
{\displaystyle S_{total}}
 and a specific surface area 
S
{\displaystyle S}
 are evaluated by the following equations:
BET theory
Transcriptome
Image analysis
Kick chart
Transporter Classification database
Shotgun sequencing
DNA sequencing
Sequencing