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# Methods and Applications of Analysis

## Volume 28 (2021)

### Number 3

### Special issue dedicated to Professor Ling Hsiao on the occasion of her 80th birthday, Part II

Guest editors: Qiangchang Ju (Institute of Applied Physics and Computational Mathematics, Beijing), Hailiang Li (Capital Normal University, Beijing), Tao Luo (City University of Hong Kong), and Zhouping Xin (Chinese University of Hong Kong)

### Finite time blowup for the 1-D semilinear generalized Tricomi equation with subcritical or critical exponents

Pages: 313 – 324

DOI: https://dx.doi.org/10.4310/MAA.2021.v28.n3.a4

#### Authors

#### Abstract

For the 1-D semilinear generalized Tricomi equation with the subcritical or critical exponents\[\partial^2_t u - t^m \partial^2_x u = {\lvert u \rvert}^p, \qquad (u(0, x), \partial_t u(0, x)) = (u_0(x), u_1(x)),\]where $t \gt 0, x \in \mathbb{R}, 1 \lt p \leq p_m = 1+ \frac{4}{m}$ and $u_i \in C^\infty_0 (\mathbb{R}) (i = 0, 1)$, we shall prove that the weak solution $u$ generally blows up in finite time. Note that for the 1‑D equation $\partial^2_t u - t^m \partial^2_x u = {\lvert u \rvert}^p$ with $p \gt p_m$, the global existence of small value weak solution u has been obtained by us. By this paper and our previous papers, we have given a systematic study on the blowup or global existence of small value solution $u$ to the equation $\partial^2_t u - t^m \Delta u = \lvert u \rvert p$ for all space dimensions and all $p \gt 1$. One main ingredient in this paper is to apply the explicit solution formula of linear generalized Tricomi equation to derive the crucial inequality $G(t) = \int_\mathbb{R} u(t, x)dx \geq Ct \ln t$ for large $t \gt 0$ and $p = p_m$ when $u_0 (x) \geq 0, u_1 (x) \geq 0$ and $(u_0 (x), u_1 (x)) \not \equiv 0$.

#### Keywords

generalized Tricomi equation, subcritical exponent, critical exponent, hypergeometric function, blowup

#### 2010 Mathematics Subject Classification

35L65, 35L67, 35L70

He Daoyin is supported by the NSFC (No. 11901103).

Yin Huicheng is supported by the NSFC (No. 11731007).

Received 11 October 2020

Accepted 28 December 2020

Published 10 June 2022