∂c
∂t
= D
∂
2
c
∂x
2
, t > 0, x ∈ (0, `), c(0, x) = ϕ(x), x ∈ [0, ` ],
D
∂c
∂x
¯
¯
¯
x=0
= bc
2
0
, D
∂c
∂x
¯
¯
¯
x=`
= −bc
2
`
, c
0
(t) ≡ c(t, 0), c
`
(t) ≡ c(t, `).
c(t, x)
D b
H
D b T
D(T ) = D
0
exp{−E
D
/[RT ]} b(T ) = b
0
exp{−E
b
/[RT ]}
D
0
, b
0
, E
D
, E
b
= const
ϕ(x) = ¯c
ϕ(x) = ¯c − A(x − `/2)
2
, A > 0. A
J(t) = bc
2
0
(t) = bc
2
`
(t)
[0, t
∗
] J(t
∗
) ≈ 0
J(t)