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HOW TO DERIVE THE EINSTEIN'S RELATION
FROM THE FICK'S ONE
(
)
2
2
2
2
2
2
2
2
2
2
0 2
2
u
u
u
u
D
dx
D
dx
t
t
x
x
u
u
u
dx
D
dx D
dx
t
x
x
x
x
u
D
dx
D
u dx
u dx
t
x
x
x
x
x
x
x
x
x
x
x
x
+
+
-
-
+
+
+
-
-
-
+
+
-
-
=
=
=
-
= -
= -
-
[
]
0
1
2
2
2
2
x
x
D
u
u dx
t
D t Cst
x
e
+
-
+
+
-
-
= -
-
=
+
E5555F
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(
)
( )
,
0
u x t
x
=
=