Introduction
Introduction of our problemIn this paper, we consider the following nonlinear parabolic equation with nonstandard growth condition: jp.x/ p.y/j Ä C log jx yj for every x, y 2 satisfying jx yj Ä 1 2 .(1.2)
Z. LI AND W. GAOg.x, t, s, /s 0, (1.4) for any .s, / 2 R R N , and for almost every .x, t/ 2 Q T .We remark that the log-Hölder continuity condition in assumption (H1), originally introduced by Zhikov [1], guarantees that smooth functions are dense in the variable exponent Sobolev space [2]. In general, see [3], they are NOT if p.x/ ¤ constant, which is an interesting feature, called Lavrentiev phenomenon. Under this condition, we can define W 1,p.x/ 0 . / as the closure of C 1 0 . / in W 1,p.x/ . /, which assists in studying the initial and boundary value problem for parabolic equations.In recent years, nonlinear partial differential equations with variable exponents have generated a good deal of interest and attention, as can be found in monograph [4] and the reference therein. Maybe, it attributes to the important physical applications in real world. Problem (1.1), or its variants, is from electro-rheological fluids model [5], which is characterized by their ability to undergo significant changes in their mechanical properties when an electric filed exerted from outside. This non-Newtonian fluids also describe some useful evolutional phenomenon in applied thermodynamics [6]. Comparing with the case when p is a constant exponent, Problem (1.1) with variable exponent is a more realistic and precise model to interpret the diffusion process. It is mainly because the space region that presents nonhomogeneous physical characteristic on the exponent p affects the growth on the state variable u, which leads to so called nonstandard growth condition. There are other applications in the calculus of variations [7], elasticity [8], image restoration [9], and so on. In particular, in image processing, the consideration of nonstandard growth condition has more advantages, chief among which is the so called staircase effect. Or more precisely, the study of variational integrals with nonstandard growth not only preserves edges in the picture but also creates edges where there were none in the original image.In 1980s, when DiPerna and Lions investigated Boltzmann equations, they firstly introduced the concept of renormalized solution [10]. Afterwards, it was used in elliptic equations [11], parabolic cases [12], or problems about conservation laws [13]. Problem (1.1) with p a constant and g D 0, or some variants of it, has been widely analyzed in the literature [14,15]. The case p D 2 was investigated in [12], while the case when the initial value u 0 D 0 was studied in [16]; when 1 < p < 2, p is a constant, and g, f , ! F D 0, the existence of renormalized solution was studied by Xu [17]. The authors of more recent studies [18,19] concentrated on the nonlinear PDEs with variable exponents, L 1 data, and g D 0. To the best of our knowledge, only a few papers deal with the renormalized solution in the setting...