Abstract
Keywords:
OrliczSobolev spaces; symmetric mountain pass theorem; quasilinear elliptic equations1 Introduction
In this note, we discuss the existence and multiplicity of solutions of the following boundary value problem:
where is a bounded domain with a smooth boundary ∂Ω. The function a is such that defined by
is an increasing homeomorphism from R onto itself and the continuous function satisfies , . Especially, when , the problem (1.1) is the wellknown pLaplacian equation. There is a large number of papers on the existence of solutions for the pLaplacian equation. But the problem (1.1) possesses more complicated nonlinearities. For example, it is inhomogeneous and has an important physical background, e.g.,
(c) generalized Newtonian fluids: , , .
So, in the discussions, some special techniques are needed, and the problem (1.1) has been studied in an OrliczSobolev space and received considerable attention in recent years; see, for instance, the papers [19]. In paper [9], Fang and Tan discussed the problem (1.1) under the conditions that was odd in t. They got the first result that when , and for , , the problem (1.1) had a sequence of solutions by genus theory. The second result is that when satisfies , , , and as , the problem (1.1) has infinitely many pairs of solutions which correspond to the positive critical values by the symmetric mountain pass theorem.
Motivated by their results, in this note, we discuss the problem (1.1) when is still odd in t but it satisfies weaker conditions than [9]; and furthermore, we need not know the behaviors of near the zero. If , we can get multiplicity of solutions by a version of the symmetric mountain pass theorem.
The paper is organized as follows. In Section 2, we present some preliminary knowledge on the OrliczSobolev spaces and give the main result. In Section 3, we make the proof.
2 Preliminaries
Obviously, the problem (1.1) allows a nonhomogeneous function p in the differential operator defining the problem (1.1). To deal with this situation, we introduce an OrliczSobolev space setting for the problem (1.1) as follows.
Let
then P and are complementary Nfunctions (see [10]), which define the Orlicz spaces and respectively.
Throughout this paper, we assume the following condition on P:
Under the condition (p), the Orlicz space coincides with the set (equivalence classes) of measurable functions such that
and is equipped with the (Luxemburg) norm, i.e.,
We will denote by the corresponding OrliczSobolev space with the norm
and define as the closure of in . In this note, we will use the following equivalent norm on :
Now, we introduce the OrliczSobolev conjugate of P, which is given by
where we suppose that
Let , . Throughout this paper, we assume that . Now, we will make the following assumptions on .
() There exists an odd increasing homeomorphism h from R to R, and nonnegative constants , such that
Let
then we can obtain complementary Nfunctions which define corresponding Orlicz spaces and .
Similar to the condition (p), we also assume the following condition on H:
In order to prove our results, we now state some useful lemmas.
Lemma 2.1[10]
Under the condition (p), the spaces, andare separable and reflexive Banach spaces.
Lemma 2.2[10]
Under the condition (), the embeddingis compact.
Lemma 2.3[2]
Let, whereEis a real Banach space andVis finite dimensional. Supposeis an even functional satisfyingand
() there is a constantsuch that;
() there is a subspaceWofEwithand there issuch that;
() consideringgiven by (), Isatisfies (PS)_{c}for.
ThenIpossesses at leastpairs of nontrivial critical points.
Using the version of the symmetric mountain pass theorem mentioned above, we can state our result as follows.
Theorem 2.1Assume thatis odd int, satisfies () withand the following assumptions:
() there existand, and, , such thatfor every, a.e. in Ω.
() there iswithsuch thatuniformly a.e. in.
Then for any given, the problem (1.1) possesses at leastkpairs of nontrivial solutions.
3 Main results and proofs
In this section, we assume that and , is called a weak solution of the problem (1.1) if
Set
and we know that the critical points of I are just the weak solutions of the problem (1.1).
For E is a separable and reflexive Banach space, then there exist (see [9]) and such that
Lemma 3.1Given, there issuch that for all, .
Proof We prove the lemma by contradiction. Suppose that there exist and for every such that . Taking , we have for every and . Hence, is a bounded sequence, and we may suppose, without loss of generality, that in . Furthermore, for every since for all . This shows that . On the other hand, by the compactness of embedding , we conclude that . This proves the lemma. □
Lemma 3.2Supposefsatisfies (), then there existandsuch that
Proof Now suppose that . From (), we know that
Consequently, considering to be chosen posteriorly by Lemma 3.1, we have for all and j sufficiently large,
Now, taking and noting that , if , we can choose such that , , and for every , , the proof is complete. □
Lemma 3.3Supposefsatisfies (). Then given, there exist a subspaceWofand a constantsuch thatand.
Proof Let and be such that , and . First, we take with . Considering , we have . Let and be such that , and . Next, we take with . After a finite number of steps, we get such that , , and for all . Let , by construction, , and for every .
Since , if , then . Now, it suffices to verify that
From the condition (), given , there is such that for every , a.e. x in ,
and
where and . Observing that W is finite dimensional and we have , , the inequality is obtained by taking ; the proof is complete. □
Lemma 3.4Supposefsatisfies (), thenIsatisfies the (PS) condition.
Noting that , , is bounded. By [9], Lemma 3.1, we know that I satisfies the (PS) condition. □
Proof of Theorem 2.1 First, we recall that , where and are defined in (3.1). Invoking Lemma 3.2, we find , and I satisfies with . Now, by Lemma 3.3, there is a subspace W of with and such that I satisfies (). Since and I is even, we may apply Lemma 2.4 to conclude that I possesses at least k pairs of nontrivial critical points. The proof is complete. □
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
All authors read and approved the final manuscript.
Acknowledgements
Project supported by Natural Science Foundation of China, Tian Yuan Special Foundation (No. 11226116), Natural Science Foundation of Jiangsu Province of China for Young Scholar (No. BK201209), the China Scholarship Council, the Fundamental Research Funds for the Central Universities (No. JUSRP11118) and Foundation for young teachers of Jiangnan University (No. 2008LQN008).
References

Clément, PH, GarcíaHuidobro, M, Manásevich, R, Schmitt, K: Mountain pass type solutions for quasilinear elliptic equations. Calc. Var. Partial Differ. Equ.. 11, 33–62 (2000). Publisher Full Text

Fukagai, N, Ito, M, Narukawa, MK: Positive solutions of quasilinear elliptic equations with critical OrliczSobolev nonlinearity on . Funkc. Ekvacioj. 49, 235–267 (2006). Publisher Full Text

Fukagai, N, Narukawa, K: On the existence of multiple positive solutions of quasilinear elliptic eigenvalue problems. Ann. Mat. Pura Appl.. 186, 539–564 (2007). Publisher Full Text

GarcíaHuidobro, M, Le, V, Manásevich, R, Schmitt, K: On the principal eigenvalues for quasilinear elliptic differential operators: an OrliczSobolev space setting. Nonlinear Differ. Equ. Appl.. 6, 207–225 (1999). Publisher Full Text

Tan, Z, Fang, F: OrliczSobolev versus Hölder local minimizer and multiplicity results for quasilinear elliptic equations. Preprint

Mihǎilescu, M, Rădulescu, V: Nonhomogeneous Neumann problems in OrliczSobolev spaces. C. R. Math.. 346, 401–406 (2008). Publisher Full Text

Bonanno, G, Bisci, GM, Rǎdulescu, VD: Quasilinear elliptic nonhomogeneous Dirichlet problems through OrliczSobolev spaces. Nonlinear Anal.. 75, 4441–4456 (2012). Publisher Full Text

Černý, R: Generalized nLaplacian: quasilinear nonhomogenous problem with critical growth. Nonlinear Anal.. 74, 3419–3439 (2011). Publisher Full Text

Fang, F, Tan, Z: Existence and multiplicity of solutions for a class of quasilinear elliptic equations: an OrliczSobolev space setting. J. Math. Anal. Appl.. 389, 420–428 (2012). Publisher Full Text

Adams, RA, Fournier, JJF: Sobolev Spaces, Academic Press, Amsterdam (2003)

Ambrosetti, A, Rabinowitz, PH: Dual variational methods in critical point theory and applications. J. Funct. Anal.. 14, 349–381 (1973). Publisher Full Text

Bartolo, P, Benci, V, Fortunato, D: Abstract critical point theorems and applications to some nonlinear problems with “strong” resonance at infinity. Nonlinear Anal. TMA. 7, 981–1012 (1983). Publisher Full Text

Silva, EAB: Critical point theorems and applications to differential equations. PhD thesis, University of WisconsinMadison (1988)