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÷ ecuaţie: R +R ↔ R* + R → P<br />
÷ reacţii parţiale:<br />
o R + R → R* + R, v = k [ R]<br />
( 1)<br />
o R* + R → R + R, = k [ R][<br />
R*]<br />
v( 2)<br />
2<br />
v( 3)<br />
= 3<br />
o R* → P, k [ R *]<br />
÷ necunoscute:<br />
o [R] = x; [R*] = y; [P] = z;<br />
÷ conservarea masei:<br />
o (R):<br />
o (R*):<br />
x & = −v<br />
+ v<br />
( 1)<br />
( 1)<br />
( 2)<br />
y& = v − v − v<br />
( 2)<br />
o (P): z & = v(<br />
3)<br />
÷ ecuaţii diferenţiale:<br />
2<br />
2<br />
o & = −k<br />
x + k xy ; & = k x − k xy − k y ; & = k y<br />
x 1 2<br />
2<br />
x = −ax<br />
+<br />
( 3)<br />
1<br />
y 1 2 3<br />
2<br />
z 3<br />
o & 2<br />
bxy ; y&<br />
= ax − bxy − cy ; z&<br />
= cy<br />
÷ abordare greşită (căutarea unei soluţii analitice e fără succes):<br />
o<br />
2<br />
x + ax<br />
y =<br />
bx<br />
&<br />
2<br />
x&<br />
+ ax<br />
d( )<br />
2<br />
x & + ax<br />
; bx<br />
2<br />
2<br />
= ax − ( x&<br />
+ ax ) − c<br />
dt<br />
bx<br />
o<br />
2<br />
d(<br />
x&<br />
+ ax ) d(<br />
bx)<br />
2<br />
bx − ( x&<br />
+ ax )<br />
2<br />
dt dt<br />
x&<br />
+ ax<br />
= −x&<br />
− c<br />
2<br />
( bx)<br />
bx<br />
o<br />
2<br />
2 2<br />
2<br />
( &x<br />
& + 2axx&<br />
) bx − bx&<br />
( x&<br />
+ ax ) = −x&<br />
b x − c(<br />
x&<br />
+ ax ) bx<br />
o<br />
2 2 2<br />
2 2<br />
3<br />
bx&x & + 2abx<br />
x&<br />
− bx&<br />
− abx x&<br />
= −x&<br />
b x − bcx&<br />
− abcx<br />
o<br />
2 2 2 2<br />
3<br />
bx&x<br />
& + abx x&<br />
− bx&<br />
+ x&<br />
b x + bcx&<br />
+ abcx = 0<br />
o<br />
2 2 2<br />
3<br />
x&x<br />
& + ax x&<br />
− x&<br />
+ x&<br />
bx + cx&<br />
+ acx = 0<br />
o<br />
2 2<br />
2<br />
3<br />
x&<br />
− ax x&<br />
− x&<br />
bx − cx&<br />
− acx<br />
&x<br />
& =<br />
x<br />
o<br />
2<br />
2<br />
3<br />
dv dv v − ( a + b)<br />
x v − cv − acx<br />
v = x&<br />
; & x & = v ; v =<br />
dx dx<br />
x<br />
÷ abordare corectă (căutarea unei soluţii numerice):<br />
o model: R +R ↔ R* + R → P; [R] = x; [R*] = y; [P] = z;<br />
2 2<br />
o ecuaţii diferenţiale: x&<br />
= −ax<br />
+ bxy ; y&<br />
= ax − bxy − cy ; z&<br />
= cy<br />
o condiţii iniţiale: x(0)=R0; y(0)=0; z(0)=0;<br />
o iteraţii:<br />
x + ( −ax<br />
2<br />
+ bx y ) Δt<br />
xi = i−1<br />
i−1<br />
i−1<br />
i−1<br />
yi 2<br />
= yi<br />
−1<br />
+ ( axi<br />
−1<br />
− bxi<br />
−1yi<br />
−1<br />
− cy i−1<br />
zi = zi<br />
−1<br />
+ cyi−1Δ<br />
) Δt<br />
<br />
o aplicaţie numerică:<br />
t<br />
x = x + ( −ax<br />
2<br />
+ bx y ) Δt<br />
<br />
y<br />
i<br />
i<br />
i<br />
y = y<br />
z = z<br />
0<br />
a = 10<br />
i−1<br />
i−1<br />
i−1<br />
= 0; z<br />
−2<br />
+ ( ax<br />
+ cy<br />
0<br />
=<br />
2<br />
i−1<br />
i−1<br />
0; x<br />
; b = 10<br />
i−1<br />
Δt<br />
0<br />
−3<br />
− bx<br />
= R<br />
i−1<br />
0<br />
; c = 10<br />
i−1<br />
y<br />
−5<br />
i−1<br />
i−1<br />
− cy<br />
i−1<br />
= 1; Δt<br />
= 10<br />
) Δt<br />
-2<br />
8