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P P$P#UV P$#QQU': S M T dt x Km r n = + Ω % # # ' ' ' n n i B Fe i cuđm i i i đm S A P t P t S = =   ∆ = ∆ + ∆  ÷   ∑ ∑ % % # # ' ' ' ' R  n n cuđm i B Fe i i i i i i đmB i P t A P t m S m m S m = = ∆ ∆ = ∆ + ≤ ∑ ∑ %' N % -+(J*K)3;W/W< /-01& 1.$2$345"67$ 581.$29$:.;< • X=>?5Y+?!<):;=>?5W<:ZY+[< )$(Y+\()/;=>?3;W-FHY +!]' • CY+?!<)4<-W-A[@:W/3Y+' D40^+9=>?Y+?!<)0(3=>?Y+ $=55W[B' =>34<:& !.'?8!$3@ /5 X2?W:;2W_%9 • `_%92?W(>Y • `a_%92?W+0( • `b_%92?W A3B CD$EF:& ! #  G9(W<9/(REc./ ∆ d  9 ∆ d e $ ∆ d  W ' R  ' ' i i tt tt rđm Pl F k U U ρ = ∆ ∑  # ' G!+2Efg5(W<hZ3W<9 /(REc  -A[c  ' # / GC2:6./()0/ % % # # ' ' ' ' ' n n cuđm B Fe i i i i i đmB P A m P t S t m S = = ∆ ∆ = ∆ + ∑ ∑ i i # # ' n k k k S Z S Z ∑ = = ∑ W-4_B i k k S Z Z ∑ ,j7B ,j_Y+03)B<> bR:ZF+ ( ) ( ) P P ' ' ' ' i i i i đm r P l x Q l U U + ∆ = ∑ ∑ ∆ d  k ∆ d  -c  3_ERA0 ∆ d  l ∆ d  0A^3)!%Ec  :[#-' HDI%& ∆ J $ & $81$" G 0?( * # E [ ] P P$@& P$Q Mx Km∈ ÷ Ω * %  ( ) P ' ' i i x đm x Q l U U ∆ = ∑ * @  r cp x U U U ∆ = ∆ − ∆ * Q 9>9/( ' R  ' ' i i tt tt rđm Pl F k U U ρ = ∆ ∑  * U !+E>gmA[>9/(R R  tc tt F F≤  P P $r x Fc  ' * & C2:6./ ∆ J $  ∆ d  k ∆ d  -c  3_ERA0 ∆ d  l ∆ d  0A^3)!UEc  :[#-'R0A0 3G ?( * # E [ ] P P$@& P$Q Mx Km∈ ÷ Ω * % 9 $ xABC xABD U U∆ ∆ P # # % % P # # @ @ 'R  'R  xABC đm xABD đm x U Q l Q l U x U Q l Q l U ∆ = + ∆ = + ( ) e $ x xABC xABD U U U∆ = ∆ ∆ 39>YE xABD U∆ :;e * @  r cp x U U U ∆ = ∆ − ∆ * Q 9 # # @ @ R  ' tt rđm Pl Pl F U U ρ + = ∆ ∆ ./ ex U∆ * U !+E>gmA[>9/(R R  tc tt F F≤  P P $r x Fc  ' * & C2:6./ ∆ J $  ( ) ( ) P P ' ' ' ' i i i i đm r P l x Q l U U + ∆ = ∑ ∑ A B C D # l % l @ l # S → n # # # # % % % % # # # # @ @ @ @ # 'R  # 'R  ABC cp đm ABD cp đm U R Q X P R Q X U U U R Q X P R Q X U U ∆ = + + + ≤ ∆ ∆ = + + + ≤ ∆ S # # # # % % % % # # # # @ @ @ @ # 'R  # 'R  ABC cp đm ABD cp đm U R Q X P R Q X U U U R Q X P R Q X U U ∆ = + + + > ∆ ∆ = + + + ≤ ∆ KDI%&L  & $81$" G 0?( * # 9!W i i i i i i S P Q S Cos ϕ ϕ = + = ∠ → * % E [ ] P P$@& P$Q Mx Km∈ ÷ Ω * @  ( ) P ' ' i i x đm x Q l U U ∆ = ∑ * Q  Uo cpđm U U ∆ = × * U  r cp x U U U ∆ = ∆ − ∆ * &  @' ' R  r kđ i i U j l Cos ρ ϕ ∆ = ∑ * V  { }  p tt kt kđ j j j= * q 9>(/6 @ '#P ' @' ' i i tt đm tt S F k U j − = !+E>?./^ r X/6BE:[m r (/6s:6EA[m' A0Ec CA0Ec$?c: 3;f:63 ABC U∆ * t C2:6 ∆ d  ≤  ∆ d  A0 ∆ d  l ∆ d  0A0$8>A-:#-'X/69W0 5c:[/69' 3G 6$ * # 9!W i i i i i i S P Q S Cos ϕ ϕ = + = ∠ → * # E [ ] P P$@& P$Q Mx Km∈ ÷ Ω * % 9 $ xABC xABD U U∆ ∆ P # # % % P # # @ @ 'R  'R  xABC đm xABD đm x U Q l Q l U x U Q l Q l U ∆ = + ∆ = + ( ) e $ x xABC xABD U U U∆ = ∆ ∆ 39>YE xABD U∆ :;e * Q  Uo cpđm U U ∆ = × * U  r cp x U U U ∆ = ∆ − ∆ * &  # # @ @ @' ' R  r kđ U j l Cos l Cos ρ ϕ ϕ ∆ = + ∑ 9 kđ j ./( ex U∆ * V  { }  p tt kt kđ j j j= * q 9>(/6 @ '#P ' @' ' i i tt đm tt S F k U j − = !+E>?./^ r X/6BE:[m r (/6s:6EA[m' * t C2:6./ ∆ J $  n # # # # % % % % # # # # @ @ @ @ # 'R  # 'R  ABC cp đm ABD cp đm U R Q X P R Q X U U U R Q X P R Q X U U ∆ = + + + ≤ ∆ ∆ = + + + ≤ ∆ ( ) ( ) P P ' ' ' ' i i i i đm r P l x Q l U U + ∆ = ∑ ∑ A B C D # l % l @ l # S → A0Ec S # # # # % % % % # # # # @ @ @ @ # 'R  # 'R  ABC cp đm ABD cp đm U R Q X P R Q X U U U R Q X P R Q X U U ∆ = + + + > ∆ ∆ = + + + ≤ ∆ M6CD+#,%&< N$281%&O3P" #' EW<:ZJ*KMM ≥ %5Y+:/6#$%p"#5Y+:/6@' %' EW/uJ*K./W:mF+ e S  e ' ' tt đmB S k S n k θ ≥ /5 k θ :;W<IG # #PP đm K θ θ θ − = + !E./^(+!4= e ' ' ' tt đmB t S k S n k k θ ≥ /5C  :;W<^(+:v!4= C  "#$@rP$@C   e tb đ S k S = G E./^(+Ww< ' #$Q'R # csyc tt đmB S k S n ≥ − /5b W W+5:vWw< #$Q/L^(+#$Q:W Rr##J*K/6' Q-R<&$5S!$3!$$5PJ o X(:;#/%W<((-:Z' o 8/\+d2d]/63/L' o `(83Z^#63/L4Wx?5^( $:;A:/\!y' o `(>63/L4!y3z:;3( !y:{/5$+,E' *()Id r X)I(j`JX r ,?(J*K r ,W<=>?' CA0Ec$?c: 3;f:63 ABC U∆ T() U 18!&VE$$+#, '-R<&$3;<$03W3;<$  X2+,-83;('  `?/W-)+=>?' Cc thit b b cspk:  J(!hB!G  ;#G[B!G60+  C ↑ $ ↓ >s09_Wx:;J*X*(/\YW0 → (+ ↑ /\ ↓ ' ! Y  I59-( Q → :; ↑  d  J< ↓ d+O!Y' /#;0813;X9 • *h0 ↓ A∆ → 9/(0$0| • *h0|!h2)I($9!O!G =3!$$:B5SJ • ,W<=>?MM=>?MM #đd tđ Z Z n = • hY!hO<=>? 0OY đm PR QX U U + ∆ =  b0OY } R  c đm PR Q X X U U + − ∆ =  A-R<&$!*$Y$$B !* X2+,-8=>?$+9)+8 →↓ (;8' (?/(3;' X?(:;7:- _G/J*KW<3s>?7% ::;!]' # # # % % % % # # 'U n U n C U U n n n = ⇒ = = ⇒ d % ~:y #  # ↑ Rv0 ↓  ⇒ d % ↓   # ↓ Rv0 ↑  ⇒ d %  ↑ z R jX= + } Z R jX= + xc j− H672!Z:[:)) • X)Id • 1+ A∆ → YOxWx(a:: → :;+a: → + $U A∆ ∆ K-R<&$3@<:&\-]<C481^3@<>81 <_ r 3@<:&\-]B •!]$W(?!]/NX •`W0?!]Wx?-,y/NX3)d3;u' r `C481 a1<59-,yu3;d a0(?!]R,yu$?!]aR,yd' M-R<&1$;<4:bB& aQW<9/u=>? P P P P $ $ $r L g C •X=>?>; → W5+-=)=>? → (W< 0(6_=2' •W<+)_2=>?0,/ P P $ P'g r = N[4)W5 @ % % P P @ % P % P '/WR  '#P 'WR  '/WR  ' '#P 'WR  x c x c U I I x j x Z U U x jZ I x α α α α − = + = + % % % ' đm P Q A R t U PR QX U U   + ∆ =  ÷   + ∆ = • $ x x I U (3;>s63y 9eW/3<=>?' • % % $U I (3;>s6 <=>?'  c Z ,jW5=>? P P P P P $ c L Z w L C C α = = ]W<