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Volume 2010, Article ID 490741,14pages doi:10.1155/2010/490741

Research Article

Nonlinear Boundary Value Problem of First-Order

Impulsive Functional Differential Equations

Kexue Zhang

1

and Xinzhi Liu

2

1School of Control Science and Engineering, Shandong University, Jinan, Shandong 250061, China 2Department of Applied Mathematics, University of Waterloo, Waterloo, ON, Canada N2L 3G1

Correspondence should be addressed to Xinzhi Liu,[email protected]

Received 8 December 2009; Accepted 30 January 2010

Academic Editor: Shusen Ding

Copyrightq2010 K. Zhang and X. Liu. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This paper investigates the nonlinear boundary value problem for a class of first-order impulsive functional differential equations. By establishing a comparison result and utilizing the method of upper and lower solutions, some criteria on the existence of extremal solutions as well as the unique solution are obtained. Examples are discussed to illustrate the validity of the obtained results.

1. Introduction

It is now realized that the theory of impulsive differential equations provides a general framework for mathematical modelling of many real world phenomena. In particular, it serves as an adequate mathematical tool for studying evolution processes that are subjected to abrupt changes in their states. Some typical physical systems that exhibit impulsive behaviour include the action of a pendulum clock, mechanical systems subject to impacts, the maintenance of a species through periodic stocking or harvesting, the thrust impulse maneuver of a spacecraft, and the function of the heart. For an introduction to the theory of impulsive differential equations, refer to1.

It is also known that the method of upper and lower solutions coupled with the monotone iterative technique is a powerful tool for obtaining existence results of nonlinear differential equations 2. There are numerous papers devoted to the applications of this method to nonlinear differential equations in the literature, see3–9and references therein. The existence of extremal solutions of impulsive differential equations is considered in papers

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nonlinear boundary value problem of a class of first-order impulsive functional differential equations. Such equations include the retarded impulsive differential equations as special cases5,12–14.

The rest of this paper is organized as follows. In Section 2, we establish a new comparison principle and discuss the existence and uniqueness of the solution for first order impulsive functional differential equations with linear boundary condition. We then obtain existence results for extremal solutions and unique solution inSection 3by using the method of upper and lower solutions coupled with monotone iterative technique. To illustrate the obtained results, two examples are discussed inSection 4.

2. Preliminaries

LetJ 0, T,T > 0,J J− {t1, t2, . . . , tp}with 0 < t1 < t2 < · · · < tp < T. We define that

P CJ {x:J → R:xis continuous for anytJ;xtkandxtkexist andxtk xtk},

P C1J {x:J → R :xis continuously differentiable for anytJ;xtk,xtkexist and

xtk xtk}. It is clear thatP CJandP C1Jare Banach spaces with respective norms

xP Csup

tJ

|xt|, xP C1xP Cx

P C. 2.1

Let us consider the following nonlinear boundary value problemNBVP:

xt ft, xt,ϕxt, tJJt1, t2, . . . , tp

,

Δxt Ik

t, xt,ϕxt, ttk, k1,2, . . . , p,

gx0, xT 0,

2.2

wheref:J×R2 Ris continuous in the second and the third variables, and for fixedx, y R,f·, x, yP CJ,gCR2,R,I

kCR3,R,k 1,2, . . . , pandϕ :P CJP CJis

continuous.

A functionxP C1Jis called a solutions of NBVP2.2if it satisfies2.2.

Remark 2.1. iIfϕxt xtand the impulsesIk depend only onxtk, the equation of

NBVP2.2reduces to the simpler case of impulsive differential equations:

xt ft, xt, tJ,

Δxtk Ikxtk, k1,2, . . . , p 2.3

which have been studied in many papers. In some situation, the impulseIkdepends also on

some other parameterse.g., the control of the amount of drug ingested by a patient at certain moments in the model for drug distribution1,3.

iiIfϕxt xθt, whereθCJ, J, the equation of NBVP2.2can be regarded as retarded differential equation which has been considered in5,12–14.

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Lemma 2.2see1. Asumme that

B0the sequence{tk}satisfies0≤t0< t1< t2<· · ·< tk<· · · withlimk→ ∞tk, B1mP C1Ris left continous attkfork1,2, . . .,

B2fork1,2, . . .,tt0,

mtptmt qt, t /tk

mtkdkmtk bk,

2.4

wherep, qCR,R,dk≥0andbkare real constants.

Then

mtmt0

t0<tk<t

dkexp

t

t0 psds

t

t0s<tk<t

dkexp

t

s

pσdσ

qsds

t0<tk<ttk<tj<t

djexp

t

tk

psds

bk.

2.5

In order to establish a comparison result and some lemmas, we will make the following assumptions on the functionϕ.

H1There exists a constantR >0 such that

ϕxtRinf

tJxt, for any xP CJ,tJ. 2.6

H2The functionϕsatisfies Lipschitz condition, that is, there exists aL >0 such that

ϕxϕyP CLxyP C,x, yP CJ. 2.7

Inspired by the ideas in5,6, we shall establish the following comparison result.

Theorem 2.3. LetmP C1Jsuch that

mt≤ −MmtNϕmt, tJ,

Δmtk≤ −Lkmtk, k1,2, . . . , p,

m0≤μmT,

2.8

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Suppose in addition that condition (H1) holds and

NReMTμ

μ

T

0s<tk<T

1−LkeMsdsp

k1

1−Lk2 2.9

thenmt≤0, fortJ.

Proof. For simplicity, we letck1−Lk,k1,2, . . . , p. Setvt mteMt, then we have

vt≤ −NeMtϕmt, tJ,

vtkckvtk, k1,2, . . . , p

v0≤μeMTvT.

, 2.10

Obviously,vt≤0 impliesmt≤0.

To showvt≤0, we suppose, on the contrary, thatvt>0 for sometJ. It is enough to consider the following cases.

ithere exists atJ, such thatvt>0, andvt≥0 for alltJ;

iithere existt, t∗∈J, such thatvt<0,vt>0.

Case (i). By2.10, we havevt ≤ 0 fort /tk andΔvtk ≤ 0,k 1,2, . . . , m, hencevtis

nonincreasing inJ, that is,vTv0. Ifμ < eMT, thenv0< vT, which is a contradiction.

IfμeMT, thenv0≤vTwhich impliesvtC >0. But from2.10, we getvt<0 for

tJ. Hence,vT< v0. It is again a contradiction.

Case (ii). Let inftJvtλ, thenλ > 0. For somei∈ {1,2, . . . , p}, there existst∗ ∈ ti, ti1

such thatvt∗ −λorvt∗ −λ. We only considervt∗ −λ, as for the casevt∗ −λ, the

proof is similar.

From2.10and conditionH1, we get

vt≤ −NeMtϕmt NeMtϕvteMtt

≤ −NReMtinf

tJ

vteMt≤ −NReMtinf

tJ{vt}

λNReMt, tJ.

2.11

Consider the inequalities

vtλNReMt, tJ,

vtkckvtk, k1,2, . . . , p.

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ByLemma 2.2, we have

vtvt

t<tk<t

ck t t

s<tk<t

ck

λNReMsds, 2.13

that is

vt≤ −λ

t<tk<t

ck λNR t t

s<tk<t

ck

eMsds. 2.14

First, we assume thatt> t. Lettt∗in2.14, then

vt∗≤ −λ

t<tk<t

ck λNR tt

s<tk<t

ck

eMsds. 2.15

Noting thatvt>0, we have

t<tk<t

ck< NR

t

t

s<tk<t

ck

eMsds. 2.16

Hence

p

k1 ck

2

p

k1

ck< NR

T

0

s<tk<T

ck

eMsds 2.17

which is a contradiction.

Next, we assume thatt< t∗. ByLemma 2.2and2.10, we have

0< vt∗≤v0

0<tk<t

ck t∗ 0

s<tk<t

ck

λNReMsds

μeMTvT

0<tk<t

ck λNR t∗ 0

s<tk<t

ck

eMsds,

2.18

then

0< μeMTvT

p

k1 ck λNR T 0

s<tk<T

ck

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SettingtT in2.14, we have

vTvt

t<tk<T

ck T t

s<tk<T

ck

λNReMsds

λ

t<tk<T

ck λNR T t

s<tk<T

ck

eMsds

≤ −λ

p

k1

ckλNR

T

0

s<tk<T

ck

eMsds

2.20

with2.19, we obtain that

0< μeMTvT

p

k1 ck λNR T 0

s<tk<T

ck

eMsds

λ

p

k1 ck λNR T 0

s<tk<T

ck

eMsds

μeMT

p

k1 ck λNR T 0

s<tk<T

ck

eMsds

μλeMT

p

k1 ck

2

μλNReMT

p

k1 ck

T

0

s<tk<T

ck

eMsds

λNR

T

0

s<tk<T

ck

eMsds,

2.21

that is,

μeMT

p

k1 ck

2

μNReMT

p

k1 ck NR T 0

s<tk<T

ck

eMsds

< NRμeMT1

T

0

s<tk<T

ck

eMsds.

2.22

Therefore,

p

k1

1−Lk2< NR

eMTμ

μ

T

0s<tk<T

1−LkeMsds 2.23

which is a contradiction. The proof ofTheorem 2.3is complete.

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Corollary 2.4. Assume that there existM > 0,N ≥ 0,0 ≤ Lk < 1, fork 1,2, . . . , psuch that

mP C1Jsatisfies2.8with0< μeMT1and

RNeMTμeMT

μ

p

k11−Lk 2

T

0

s<tk<T1−Lkds

2.24

thenmt≤0, fortJ.

Remark 2.5. Setting μ ≡ 1, Corollary 2.4 reduces to the Theorem 2.3 of Li and Shen 6. Therefore,Theorem 2.3andCorollary 2.4develops and generalizes the result in6.

Remark 2.6. We show some examples of functionϕsatisfyingH1.

i ϕxt xθt, whereθCJ×J, satisfiesH1withR1,

ϕxt xθt≥inf

tJxt, fortJ. 2.25

ii ϕxt t0Txsds, satisfiesH1withRT,

ϕxt

tT

0

xsdstTinf

tJxtTinftJxt, fortJ. 2.26

Consider the linear boundary value problemLBVP

yt Myt Nϕyt σt, tJ,

Δytk Lkytk Ik

tk, ηtk,

ϕηtkLkηtk, k1,2, . . . , p,

0, ηTM1

y0−η0−M2

yTηT0,

2.27

whereM >0,N≥0, 0≤Lk<1,k1,2, . . . , p, andη, σP CJ.

By direct computation, we have the following result.

Lemma 2.7. yP C1Jis a solution of LBVP2.27if and only ifyis a solution of the impulsive integral equation

yt CeMtBη

T

0

Gt, sσsNϕysds

0<tk<T

Gt, tkLkytk Ik

tk, ηtk,

ϕηtkLkηtk

, tJ,

2.28

whereBη0, ηT M1η0−M2ηT,C M1−M2eMT−1,M1/M2eMT and

Gt, s

⎧ ⎨ ⎩

CM2eMstTeMst, 0≤s < tT

CM2eMstT, 0≤tsT

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Lemma 2.8. Let (H2) hold. Suppose further

NLT

p

k1

|Lk|

r <1, rmax{|CM1|,|CM2|}, C

M1−M2eMT

−1

, 2.30

whereM >0,N≥0,M1/M2eMT, then LBVP2.27has a unique solution.

ByLemma 2.7and Banach fixed point theorem, the proof ofLemma 2.8is apparent, so we omit the details.

3. Main Results

In this section, we use monotone iterative technique to obtain the existence results of extremal solutions and the unique solution of NBVP2.2. We shall need the following definition.

Definition 3.1. A functionαP C1Jis said to be a lower solution of NBVP2.2if it satisfies

αtft, αt,ϕαt, tJ,

ΔαtkIk

tk, αtk,

ϕαtk, k1,2, . . . , p,

0, αT≤0.

3.1

Analogously,βP C1Jis an upper solution of NBVP2.2if

βtft, βt,ϕβt, tJ,

ΔβtkIk

tk, βtk,

ϕβtk, k1,2, . . . , p,

0, βT≥0.

3.2

For convenience, let us list the following conditions.

H3There exist constantsM >0,N≥0 such that

ft, x, ϕxft, x, ϕx≥ −MxxNϕxϕx 3.3

whereverα0txxβ0t.

H4There exist constants 0≤Lk<1 fork1,2, . . . , psuch that

Ik

tk, x, ϕx

Ik

tk, x, ϕx

≥ −Lkxx, k1,2, . . . , p 3.4

whereverα0tkxxβ0tk.

H5The functionϕsatisfies

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H6There exist constantsM1,M2with 0< M2eMTM1such that

gx, ygx, yM1xxM2

yy 3.6

whereverα00≤xxβ00, andα0Tyyβ0T.

Letα0, β0 {xP C1J : α0txtβ0t, for alltJ}. Now we are in the

position to establish the main results of this paper.

Theorem 3.2. Let (H1)–(H6) and inequalities2.9and2.30hold. Assume further that there exist

lower and upper solutionsα0andβ0of NBVP2.2, respectively, such thatα0 ≤β0onJ. Then there

exist monotone sequences{αn},{βn} ⊂ P C1Jwithα0 ≤ · · · ≤ αn ≤ · · · ≤ βn ≤ · · · ≤ β0, such

thatlimn→ ∞αnxt,limn→ ∞βn xtuniformly onJ. Moreover,xt,xtare minimal and

maximal solutions of NBVP2.2inα0, β0, respectively.

Proof. For anyηα0, β0, consider LVBP2.27with

σt ft, ηt,ϕηtMηt Nϕηt. 3.7

By Lemma 2.8, we know that LBVP 2.27 has a unique solution yP C1J. Define an

operatorA:P CJP CJbyyAη, then the operatorAhas the following properties:

aα0≤0,0 ≤β0,

b1≤2, ifα0≤η1≤η2≤β0.

To provea, letα10andmt α0tα1t.

mt α0tα1t

ft, α0t,

ϕα0

t

−−1tN

ϕα1

t ft, α0t,

ϕα0

tMα0t N

ϕα0

t

≤ −MmtNϕmt,

Δmtk Δα0tk−Δα1tk

Ik

tk, α0tk,

ϕα0

tk−−Lkα1tk Ik

tk, α0tk,

ϕα0

tkLkα0tk

≤ −Lkmtk,

m0 α00−α10

α00−

− 1

M100, α0T α00 M2

M1α1Tα0T

M2

M1 mT.

3.8

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To proveb, setmt x1tx2t, wherex1 1andx2 2. UsingH3,H4

andH6, we get

mt x1tx2t

1tx1t

Nϕη1

tϕx1

tft, η1t,

ϕη1

t

2tx2t

Nϕη2

tϕx2

tft, η2t,

ϕη2

t

≤ −MmtNϕmt,

Δmtk Δx1tk−Δx2tk

Lk

η1tkx1tk

Ik

tk, η1tk,

ϕη1

tk

Lk

η2tkx2tk

Ik

tk, η2tk,

ϕη2

tk

≤ −Lkmtk,

m0 x10−x20

− 1

M1

10, η1T

η10 M2 M1

x1Tη1T

1

M1

20, η2T

η20− M2 M1

x2Tη2T

M2

M1 mT.

3.9

ByTheorem 2.3, we getmt≤0 fortJ, that is,1≤2, thenbis proved.

Letαn Aαn−1and βn Aβn−1 forn 1,2,3, . . . .By the propertiesaandb, we

have

α0≤α1≤ · · · ≤αn≤ · · · ≤βn ≤ · · · ≤β1≤β0. 3.10

By the definition of operatorA, we have that{αn}and{βn}are uniformly bounded inα0, β0.

Thus{αn}and{βn}are uniformly bounded and equicontinuous inα0, β0. By Arzela-Ascoli

Theorem and3.10, we know that there existx∗,x∗inα0, β0such that

lim

n→ ∞αnt xt, nlim→ ∞βnt x

t uniformly onJ

3.11

Moreover,xt,xtare solutions of NBVP2.2inα0, β0.

To prove thatx,x∗ are extremal solutions of NBVP 2.2, letutα0, β0 be any

solution of NBVP2.2, that is,

ut ft, ut,ϕut, tJ,

Δutk Ik

tk, utk,

ϕutk, k1,2, . . . , p,

gu0, uT 0.

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ByTheorem 2.3and Induction, we getαntutβntwithtJandn1,2,3, . . .which implies thatxtutxt, that is,xandx∗are minimal and maximal solution of NBVP

2.2inα0, β0, respectively. The proof is complete.

Theorem 3.3. Let the assumptions ofTheorem 3.2hold and assume the following.

H7There exist constantsM > 0,N≥0such that

ft, x, ϕxft, x, ϕx≤ −MxxNϕxϕx, 3.13

whereα0txxβ0t.

H8There exist constants0≤Lk<1,k1,2, . . . , psuch that

Ik

tk, x, ϕx

Ik

tk, x, ϕx

≤ −Lkxx, k1,2, . . . , p, 3.14

whereα0tkxxβ0tk.

H9There exist constantsM1,M2with0<M2eMT <M1such that

gx, ygx, yM1xxM2

yy 3.15

wheneverα00≤xxβ00, andα0Tyyβ0T.

Then NBVP2.2has a unique solution inα0, β0.

Proof. By Theorem 3.2, we know that there exist x, x∗ ∈ α0, β0, which are minimal and

maximal solutions of NBVP2.2withxtxt, tJ.

Letmt xtxt. UsingH7,H8, andH9, we get

mt xtxtft, xt,ϕxtft, xt,ϕxt

≤ −Mm tNϕmt,

Δmtk Δxtk−Δxtk Ik

tk, xtk,

ϕxtkIk

tk, xtk,ϕxtk

Lkmtk,

m0 x∗0−x∗0≤

M2

M1

xTxT

M2

M1 mT.

3.16

ByTheorem 2.3, we have thatmt< 0,tJ, that is,xtxt. Hencext xt, this

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4. Examples

To illustrate our main results, we shall discuss in this section some examples.

Example 4.1. Consider the problem

xt −1

10−|sint|x−2

5e−2π

3

t1

t

xsds−sin t 4

2

4

3e

−2π, t0, T, t /t k,

Δxtk −1

2e

π/2xtk3

tk1

tk

xsds−sintk 4

1/7

4

17e

π/2cost

k, k1,

x0− 1 2xT

1 6π

T

0

xsds0,

4.1

whereT 2π,k1,t1π.

Let

ϕxt

t1

t

xsds−sin t 4,

ft, x, y−1

10−|sint|x−2

5e−2π

3 y

24

3e

−2π,

I1

t, x, y−1

2e

π/2x3 y1/7 4

17e

π/2cost.

4.2

Settingα0t≡2 andβ0t≡3, it is easy to verify thatα0tis a lower solution, andβ0tis an

upper solution withα0tβ0t.

FortJ, and 2≤xtxt≤3, we have

ϕx≥1≥ 1

3inftJxt,

ϕxϕxϕxx,

ϕxϕx

t1

t

xsxsdsxx.

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SettingM 1/2,N e−2π/6,L1,R 1/3,L

1 1/2eπ/2andM1 1,M2 1/2, then

conditionsH1–H6are all satisfied:

2π

0 s<tk<2π

1−LkeMsds

π

0

1−L1eMsds

2π

π

eMsds≈43.4893,

p

k1

1−Lk2 1−L12

1−1 2e

π/2 20.8029,

NReMT M

2/M1

M2/M1

21

18e2π ≈0.0049,

NReMT M

2/M1

M2/M1

2π

0 s<tk<2π

1−LkeMsds≈0.2131<0.8029,

NLT

p

k1

|Lk|

r NLTL1CM1 ≈0.1082<1,

4.4

then inequalities2.9and2.30are satisfied. ByTheorem 3.2, problem4.1has extremal solutionsx, x∗∈α0, β0.

Example 4.2. Consider the problem

xt −1

2xt

e−3π

1

e2x−13

2, t∈0, T, t /tk,

Δxtk −2eπxtk2 e2xtk11/50cost

k, k1,

x0 1 2xT,

4.5

whereT 2π,k1,t1π.

Let

ϕxe2x−1,

ft, x, y− 1

10−|sint|x−2

5 e−3π

161y

2

e412

16e3πeπ1,

I1

t, x, y−2eπx−2 y1/50cost.

4.6

Settingα0t≡ 2 andβ0t ≡3, thenα0tis a lower solution, andβ0tis an upper solution

withα0tβ0t.

FortJ, and 2≤xtxt≤3, we haveϕx e2x1x,ϕxϕxϕxx, and

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N e−3π/eπ 1,L 14e6,R 1, L

1 2eπ andM1 1,M2 1/2, then conditions

H1–H6are all satisfied:

!p

k11−Lk 2

2π

0

!

s<tk<2π1−Lkds

−22

2πeπeπ1 ≈0.1388,

NReMT M

2/M1

eMT

M2/M1

21

e2πeπ1 ≈0.0037<0.1388,

NLT

p

k1

|Lk|

r NLTL1CM1 ≈0.2095<1,

4.7

then inequalities2.24and2.30are satisfied. ByCorollary 2.4and Theorem 3.2, problem

4.5has extremal solutionsx, x∗∈α0, β0.

Moreover, letM1/2,Ne−3π/eπ1,L

12eπandM11,M2 1/2. It is easy

to see that conditionsH7–H9are satisfied. By Corollary 2.4 and Theorem 3.3, problem

4.5has an unique solution inα0, β0.

References

1 V. Lakshmikanthan, D. D. Bainov, and P. S. Simeonov,Theory of Impulsive Differential Equations, World Scientific, Singapore, 1989.

2 D. Guo and V. Lakshmikantham,Nonlinear Problems in Abstract Cones, vol. 5 ofNotes and Reports in Mathematics in Science and Engineering, Academic Press, Boston, Mass, USA, 1988.

3 D. Franco, E. Liz, J. J. Nieto, and Y. V. Rogovchenko, “A contribution to the study of functional differential equations with impulses,”Mathematische Nachrichten, vol. 218, pp. 49–60, 2000.

4 J. J. Nieto and R. Rodr´ıguez-L ´opez, “Boundary value problems for a class of impulsive functional equations,”Computers & Mathematics with Applications, vol. 55, no. 12, pp. 2715–2731, 2008.

5 L. Chen and J. Sun, “Nonlinear boundary value problem of first order impulsive functional differential equations,”Journal of Mathematical Analysis and Applications, vol. 318, no. 2, pp. 726–741, 2006.

6 L. Li and J. Shen, “Periodic boundary value problems for functional differential equations with impulses,”Mathematica Scientia, vol. 25A, pp. 237–244, 2005.

7 X. Liu and D. Guo, “Periodic boundary value problems for a class of second-order impulsive integro-differential equations in Banach spaces,”Journal of Mathematical Analysis and Applications, vol. 216, no. 1, pp. 284–302, 1997.

8 D. Guo and X. Liu, “Periodic boundary value problems for impulsive integro-differential equations in Banach spaces,”Nonlinear World, vol. 3, no. 3, pp. 427–441, 1996.

9 X. Liu and D. Guo, “Initial value problems for first order impulsive integro-differential equations in Banach spaces,”Communications on Applied Nonlinear Analysis, vol. 2, no. 1, pp. 65–83, 1995.

10 D. Guo and X. Liu, “First order impulsive integro-differential equations on unbounded domain in a Banach space,”Dynamics of Continuous, Discrete and Impulsive Systems, vol. 2, no. 3, pp. 381–394, 1996.

11 D. Franco and J. J. Nieto, “First-order impulsive ordinary differential equations with anti-periodic and nonlinear boundary conditions,”Nonlinear Analysis: Theory, Methods & Applications, vol. 42, no. 2, pp. 163–173, 2000.

12 X. Yang and J. Shen, “Nonlinear boundary value problems for first order impulsive functional differential equations,”Applied Mathematics and Computation, vol. 189, no. 2, pp. 1943–1952, 2007.

13 W. Ding, J. Mi, and M. Han, “Periodic boundary value problems for the first order impulsive functional differential equations,”Applied Mathematics and Computation, vol. 165, no. 2, pp. 433–446, 2005.

References

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