INTERNATIONAL JOURNAL OF COMPUTER MATHEMATICS 1593
• s(t): the expected percentage of susceptible nodes at time t, s(t) := S(t)/N.
• l(t): the expected percentage of latent nodes at time t, l(t) := L(t)/N.
• b(t): the expected percentage of bursting nodes at time t, b(t) := B(t)/N.Thus,s(t) + l(t) +
b(t) = 1.
• N
k
: the total number of k-degree nodes in the Internet. Then,
k
N
k
= N.
• S
k
(t): the expected number of susceptible k-degree nodes at time t.Then,
k
S
k
(t) = S(t).
• L
k
(t): the expected number of latent k-degree nodes at time t.Then,
k
L
k
(t) = L(t).
• B
k
(t): the expected number of bursting k-degree nodes at time t.Then,
k
B
k
(t) = B(t).
• s
k
(t): the expected percentage of susceptible k-degree nodes at time t, s
k
(t) := S
k
(t)/N
k
.
• l
k
(t): the expected percentage of latent k-degree nodes at time t, l
k
(t) := L
k
(t)/N
k
.
• b
k
(t): the expected percentage of bursting k-degree nodes at time t, b
k
(t) := B
k
(t)/N
k
.Thus,
s
k
(t) + l
k
(t) + b
k
(t) = 1.
• s(t) := (s
1
(t), s
2
(t), ..., s
(t)).
• l(t) := (l
1
(t), l
2
(t), ..., l
(t)).
• b(t) := (b
1
(t), b
2
(t), ..., b
(t)).
• N
(r)
: the total number of removable storage media in the Internet.
• S
(r)
(t): the expected number of susceptible removable storage media in the Internet at time t.
• I
(r)
(t): the expected number of infected removable storage media in the Internet at time t.Then,
S
(r)
(t) + I
(r)
(t) = N
(r)
.
• s
(r)
(t): the expected percentage of susceptible removable storage media in the Internet at time t,
that is, s
(r)
(t) := S
(r)
(t)/N
(r)
.
• i
(r)
(t): the expected percentage of infected removable storage media in the Internet at time t,that
is, i
(r)
(t) := I
(r)
(t)/N
(r)
.Then,s
(r)
(t) + i
(r)
(t) = 1.
We sha ll foc us on the change of S
k
(t), L
k
(t), B
k
(t), S
(r)
(t),andI
(r)
(t) (equivalently, the change of
l
k
(t), b
k
(t),andi
(r)
(t)). For that purpose, let us make the following assumptions.
(A1) The topology of the Internet is unvaried, implying that N and all N
k
are unvaried.
(A2) The total number of removable storage media in the Internet, N
(r)
,isunvaried.
(A3) A susceptible node gets infected by an infected node and becomes latent with constant
probability per unit time β
1
> 0.
(A4) A susceptible node gets infected by an infected removable storage medium and becomes latent
with constant probability per unit time β
2
> 0.
(A5) A susceptible removable storage medium gets infected by an infected node with constant
probability per unit time β
3
> 0.
(A6) A latent node becomes bursting with constant probability per unit time α>0.
(A7) An infected node gets cured and becomes susceptible with constant probability per unit time
γ
1
> 0.
(A8) An infected removable storage medium gets cured and becomes susceptible with constant
probability per unit time γ
2
> 0.
Following Yang et al. [40], the following additional assumption is also incorporated.
(A9) The probability that an edge has a latent node as one endpoint does not depend on the degree of
the other endpoint and, hence, depends only on l(t). Likewise, the probability that an edge has
a breaking-out node as one endpoint depends only on b(t).Let
1
(l(t)) and
2
(b(t)) denote
these two probabilities, respectively.
Direct probabilistic calculations yield
1
(l(t)) =
1
k
k
kp
k
l
k
(t),
2
(b(t)) =
1
k
k
kp
k
b
k
(t),(1)