arXiv subjects

Jifeng Chu

Publications and source records attributed to Jifeng Chu.

8 recordsLinked to original sources

arXiv2026

Optimal bounds for embedded eigenvalues of one-dimensional discrete Schr\"odinger operators with decaying potentials

In this paper, we consider one-dimensional discrete Schr\"odinger operators \begin{align} Hu(n)=(\Delta+V)u(n)\nonumber \end{align} on $\ell^2(\mathbb{N})$ with a self-adjoint boundary condition at $n=0$, where $\Delta$ denotes the discrete Laplacian and $V(n)$ is a real-valued perturbation satisfying $$V(n)=\frac{O(1)}{1+n}.$$ We determine the sharp transition for the asymptotic coefficient of $V$ governing the existence and nonexistence of embedded eigenvalues.

math-ph↗

arXiv2026

Large-Amplitude Steady Solitary Water Waves with General Vorticity

In this paper, we study two-dimensional steady solitary gravity waves propagating along the surface of a fluid of finite depth. In particular, we can deal with general vorticity distributions and overhanging wave profiles. By conformal mappings, we reformulate the problem into an overdetermined elliptic system coupled with an elliptic boundary value problem in a fixed strip domain. To avoid imposing extra constraints on vorticity function, we further reformulate the problem into the form of an abstract operator. Based on the formulations, the existence of small-amplitude solitary waves is proved by the center manifold reduction method, while the large-amplitude waves are obtained based on the analytic global bifurcation theorem.

math.AP↗

arXiv2025

Explicit sharp bounds for all nodes of Sturm-Liouville operators with potentials in $L^1$ balls

For the classical Sturm-Liouville operators, we prove the sharp bounds for all nodes of eigenfunctions by regarding these nodes as nonlinear functionals of potential $q\in L^1[0,1]$. By studying the optimization problems to minimize or to maximize the nodes $\{ T_{i,m}\}$ subject to the constraint $\|q\|_{1}=r$ with $r>0$ and using the strong continuity of the nodes in potentials, we obtain the explicit expressions for the sharp bounds, which are given as elementary functions.

math.SP↗

arXiv2025

Weak separability and partial Fermi isospectrality of discrete periodic Schrödinger operators

In this paper, we consider the discrete periodic Schrödinger operators $Δ+V$ on $\Z^d$, where $V$ is $Γ$-periodic with $Γ=q_1 \mathbb{Z}\oplus q_2\mathbb{Z}\oplus\cdots\oplus q_d\mathbb{Z}$ and positive integers $q_j$, $j=1,2,\cdots,d,$ are pairwise coprime. We introduce the notions of generalized partial Fermi isospectrality and weak separability, and prove that two generalized partially Fermi isospectral potentials have the same weak separability. As a direct application, we can prove that two potentials have the same $(d_1,d_2,\cdots,d_r)$-separability by assuming that they are generalized partially Fermi isospectral, instead of the Fermi isospectrality or Floquet isospectrality. Besides, we prove that each couples of components of the generalized Fermi isospectral potentials are Floquet isospectral in some sense.

math.SP↗

arXiv2019

Constant vorticity geophysical waves with centripetal forces and at arbitrary latitude

We consider three-dimensional geophysical flows at arbitrary latitude and with constant vorticity beneath a wave train and above a flat bed in the $\beta$-plane approximation with centripetal forces. We consider the $f$-plane approximation as well as the $\beta$-plane approximation. For the $f$-plane approximation, we prove that there is no bounded solution. For the $\beta$-plane approximation, we show that the flow is necessarily irrotational and the free surface is necessarily flat if it exhibits a constant vorticity. Our results reveal some essential differences from those results in the literature, due to the presence of centripetal forces. Moreover, for the case exhibiting the surface tension, we prove that there are no flows exhibiting constant vorticity.

math.AP↗

arXiv2014

Nonuniform dichotomy spectrum and reducibility for nonautonomous equations

For nonautonomous linear differential equations with nonuniform hyperbolicity, we introduce a definition for nonuniform dichotomy spectrum, which can be seen as a generalization of Sacker-Sell spectrum. We prove a spectral theorem and use the spectral theorem to prove a reducibility result.

math.DS↗

arXiv2014

Nonuniform dichotomy spectrum and reducibility for nonautonomous difference equations

For nonautonomous linear difference equations, we introduce the notion of the so-called nonuniform dichotomy spectrum and prove a spectral theorem. Moreover, we introduce the notion of weak kinematical similarity and prove a reducibility result by the spectral theorem.

math.DS↗

arXiv2007

Existence of positive solutions for nonlinear systems

This paper deals with the existence of positive solutions for the nonlinear system q(t)ϕ(p(t)u'_{i}(t)))'+f^{i}(t,\textbf{u})=0,\quad 0<t<1,\quad i=1,2,...,n. This system often arises in the study of positive radial solutions of nonlinear elliptic system. Here $\textbf{u}=(u_{1},...,u_{n})$ and $f^{i}, i=1,2,...,n$ are continuous and nonnegative functions, $p(t), q(t)\hbox{\rm :} [0,1]\to (0,\oo)$ are continuous functions. Moreover, we characterize the eigenvalue intervals for (q(t)ϕ(p(t)u'_{i}(t)))'+λh_{i}(t)g^{i} (\textbf{u})=0, \quad 0<t<1,\quad i=1,2,...,n. The proof is based on a well-known fixed point theorem in cones.

math.AP↗