Pub Date : 2026-02-01Epub Date: 2025-10-10DOI: 10.1016/j.na.2025.113942
Anna Lagemann, Heiko von der Mosel
Vladimir Arnold defined three invariants for generic planar immersions, i.e. planar curves whose self-intersections are all transverse double points. We use a variational approach to study these invariants by investigating a suitably truncated knot energy, the tangent-point energy. We prove existence of energy minimizers for each truncation parameter in a class of immersions with prescribed winding number and Arnold invariants, and establish Gamma convergence of the truncated tangent-point energies to a limiting renormalized tangent-point energy as . Moreover, we show that any sequence of minimizers subconverges in , and the corresponding limit curve has the same topological invariants, self-intersects exclusively at right angles, and minimizes the renormalized tangent-point energy among all curves with right self-intersection angles. In addition, the limit curve is an almost-minimizer for all of the original truncated tangent-point energies as long as the truncation parameter is sufficiently small. Therefore, this limit curve serves as an “optimal” curve in the class of generic planar immersions with prescribed winding number and Arnold invariants.
Vladimir Arnold定义了一般平面浸入式的三个不变量,即自交均为横向双点的平面曲线。我们使用变分的方法来研究这些不变量,通过研究一个适当截断的结能量,切点能量。在给定圈数和Arnold不变量的浸入式中,证明了每一个截断参数δ>;0的能量极小值的存在性,并建立了截断的切点能量的伽玛收敛到一个极限重归一化切点能量为δ→0。此外,我们还证明了任何最小值序列在C1中都是子收敛的,并且相应的极限曲线具有相同的拓扑不变量,在直角处完全自交,并且在所有自交角为直角的曲线中极小化了的切点能量。此外,只要截断参数δ足够小,对于所有原始截断的切点能量,极限曲线几乎是最小的。因此,该极限曲线可作为具有规定圈数和阿诺德不变量的一般平面浸没的一类“最优”曲线。
{"title":"Optimal planar immersions of prescribed winding number and Arnold invariants","authors":"Anna Lagemann, Heiko von der Mosel","doi":"10.1016/j.na.2025.113942","DOIUrl":"10.1016/j.na.2025.113942","url":null,"abstract":"<div><div>Vladimir Arnold defined three invariants for generic planar immersions, i.e. planar curves whose self-intersections are all transverse double points. We use a variational approach to study these invariants by investigating a suitably truncated knot energy, the tangent-point energy. We prove existence of energy minimizers for each truncation parameter <span><math><mrow><mi>δ</mi><mo>></mo><mn>0</mn></mrow></math></span> in a class of immersions with prescribed winding number and Arnold invariants, and establish Gamma convergence of the truncated tangent-point energies to a limiting renormalized tangent-point energy as <span><math><mrow><mi>δ</mi><mo>→</mo><mn>0</mn></mrow></math></span>. Moreover, we show that any sequence of minimizers subconverges in <span><math><msup><mrow><mi>C</mi></mrow><mrow><mn>1</mn></mrow></msup></math></span>, and the corresponding limit curve has the same topological invariants, self-intersects exclusively at right angles, and minimizes the renormalized tangent-point energy among all curves with right self-intersection angles. In addition, the limit curve is an almost-minimizer for all of the original truncated tangent-point energies as long as the truncation parameter <span><math><mi>δ</mi></math></span> is sufficiently small. Therefore, this limit curve serves as an “optimal” curve in the class of generic planar immersions with prescribed winding number and Arnold invariants.</div></div>","PeriodicalId":49749,"journal":{"name":"Nonlinear Analysis-Theory Methods & Applications","volume":"263 ","pages":"Article 113942"},"PeriodicalIF":1.3,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145270052","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-09-24DOI: 10.1016/j.na.2025.113943
Lukas Bundrock, Tiziana Giorgi, Robert Smits
We establish rigorous quantitative inequalities for the first eigenvalue of the generalized -Robin problem, for both the classical diffusion absorption case, where the Robin boundary parameter is positive, and the superconducting generation regime (), where the boundary acts as a source. In bounded domains, we use a unified approach to derive a precise asymptotic behavior for all and all small real , improving existing results in various directions, including requiring weaker boundary regularity for the case of the classical 2-Robin problem, studied in the fundamental work by René Sperb. In exterior domains, we characterize the existence of eigenvalues, establish general inequalities and asymptotics as for the first eigenvalue of the exterior of a ball, and obtain some sharp geometric inequalities for convex domains in two dimensions.
{"title":"Behavior of absorbing and generating p-Robin eigenvalues in bounded and exterior domains","authors":"Lukas Bundrock, Tiziana Giorgi, Robert Smits","doi":"10.1016/j.na.2025.113943","DOIUrl":"10.1016/j.na.2025.113943","url":null,"abstract":"<div><div>We establish rigorous quantitative inequalities for the first eigenvalue of the generalized <span><math><mi>p</mi></math></span>-Robin problem, for both the classical diffusion absorption case, where the Robin boundary parameter <span><math><mi>α</mi></math></span> is positive, and the superconducting generation regime (<span><math><mrow><mi>α</mi><mo><</mo><mn>0</mn></mrow></math></span>), where the boundary acts as a source. In bounded domains, we use a unified approach to derive a precise asymptotic behavior for all <span><math><mi>p</mi></math></span> and all small real <span><math><mi>α</mi></math></span>, improving existing results in various directions, including requiring weaker boundary regularity for the case of the classical 2-Robin problem, studied in the fundamental work by René Sperb. In exterior domains, we characterize the existence of eigenvalues, establish general inequalities and asymptotics as <span><math><mrow><mi>α</mi><mo>→</mo><mn>0</mn></mrow></math></span> for the first eigenvalue of the exterior of a ball, and obtain some sharp geometric inequalities for convex domains in two dimensions.</div></div>","PeriodicalId":49749,"journal":{"name":"Nonlinear Analysis-Theory Methods & Applications","volume":"262 ","pages":"Article 113943"},"PeriodicalIF":1.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145157798","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-09-03DOI: 10.1016/j.na.2025.113915
Stefano Biagi , Giovanni Cupini , Elvira Mascolo
We consider a class of energy integrals, associated to nonlinear and non-uniformly elliptic equations, with integrands satisfying anisotropic -growth conditions of the form for some exponents , and non-negative functions subject to suitable summability assumptions. We prove the local boundedness of scalar local quasi-minimizers of such integrals.
{"title":"Local boundedness for solutions of a class of non-uniformly elliptic anisotropic problems","authors":"Stefano Biagi , Giovanni Cupini , Elvira Mascolo","doi":"10.1016/j.na.2025.113915","DOIUrl":"10.1016/j.na.2025.113915","url":null,"abstract":"<div><div>We consider a class of energy integrals, associated to nonlinear and non-uniformly elliptic equations, with integrands <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>x</mi><mo>,</mo><mi>u</mi><mo>,</mo><mi>ξ</mi><mo>)</mo></mrow></mrow></math></span> satisfying anisotropic <span><math><mrow><msub><mrow><mi>p</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>,</mo><mi>q</mi></mrow></math></span>-growth conditions of the form <span><math><mrow><msubsup><mrow><mo>∑</mo></mrow><mrow><mi>i</mi><mo>=</mo><mn>1</mn></mrow><mrow><mi>n</mi></mrow></msubsup><msub><mrow><mi>λ</mi></mrow><mrow><mi>i</mi></mrow></msub><mrow><mo>(</mo><mi>x</mi><mo>)</mo></mrow><msup><mrow><mrow><mo>|</mo><msub><mrow><mi>ξ</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>|</mo></mrow></mrow><mrow><msub><mrow><mi>p</mi></mrow><mrow><mi>i</mi></mrow></msub></mrow></msup><mo>≤</mo><mi>f</mi><mrow><mo>(</mo><mi>x</mi><mo>,</mo><mi>u</mi><mo>,</mo><mi>ξ</mi><mo>)</mo></mrow><mo>≤</mo><mi>μ</mi><mrow><mo>(</mo><mi>x</mi><mo>)</mo></mrow><mfenced><mrow><msup><mrow><mrow><mo>|</mo><mi>ξ</mi><mo>|</mo></mrow></mrow><mrow><mi>q</mi></mrow></msup><mo>+</mo><msup><mrow><mrow><mo>|</mo><mi>u</mi><mo>|</mo></mrow></mrow><mrow><mi>γ</mi></mrow></msup><mo>+</mo><mn>1</mn></mrow></mfenced></mrow></math></span> for some exponents <span><math><mrow><mi>γ</mi><mo>≥</mo><mi>q</mi><mo>≥</mo><msub><mrow><mi>p</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>></mo><mn>1</mn></mrow></math></span>, and non-negative functions <span><math><mrow><msub><mrow><mi>λ</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>,</mo><mi>μ</mi></mrow></math></span> subject to suitable summability assumptions. We prove the local boundedness of scalar local quasi-minimizers of such integrals.</div></div>","PeriodicalId":49749,"journal":{"name":"Nonlinear Analysis-Theory Methods & Applications","volume":"262 ","pages":"Article 113915"},"PeriodicalIF":1.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144988180","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-09-20DOI: 10.1016/j.na.2025.113946
Alessandro Fonda , Giuliano Klun , Andrea Sfecci
We propose some new sufficient conditions for the existence of periodic solutions of an asymmetric oscillator with a positive damping term. Our results are complemented by an example where, in some situations, no periodic solutions may exist. This fact is well known in the undamped case, when the resonance phenomenon may appear. However, the damped case presents some unintuitive features which have not been so thoroughly studied in the literature, and the overall picture still has several aspects which need to be better understood.
{"title":"On the existence of periodic solutions for damped asymmetric oscillators","authors":"Alessandro Fonda , Giuliano Klun , Andrea Sfecci","doi":"10.1016/j.na.2025.113946","DOIUrl":"10.1016/j.na.2025.113946","url":null,"abstract":"<div><div>We propose some new sufficient conditions for the existence of periodic solutions of an asymmetric oscillator with a positive damping term. Our results are complemented by an example where, in some situations, no periodic solutions may exist. This fact is well known in the undamped case, when the resonance phenomenon may appear. However, the damped case presents some unintuitive features which have not been so thoroughly studied in the literature, and the overall picture still has several aspects which need to be better understood.</div></div>","PeriodicalId":49749,"journal":{"name":"Nonlinear Analysis-Theory Methods & Applications","volume":"262 ","pages":"Article 113946"},"PeriodicalIF":1.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145094803","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-09-11DOI: 10.1016/j.na.2025.113933
Yu Gan , Zhaowen Zheng , Kun Li , Jing Shao
In this paper, we obtain the sharp estimate of the first positive eigenvalue for the beam equation with Lidstone boundary condition, where weight function is allowed to change sign. We first establish a variational characterization for the first positive eigenvalue of the measure differential equation (MDE) and solve the corresponding minimization problem of the first positive eigenvalue for the MDE, where is a suitable measure. Then by finding the relationship between minimization problem for the first positive eigenvalue of ordinary differential equation (ODE) and that of MDE, we obtain the explicit sharp lower bound of the first positive eigenvalue for the indefinite beam equation.
{"title":"Minimization of the first positive eigenvalue for the beam equation with indefinite weight","authors":"Yu Gan , Zhaowen Zheng , Kun Li , Jing Shao","doi":"10.1016/j.na.2025.113933","DOIUrl":"10.1016/j.na.2025.113933","url":null,"abstract":"<div><div>In this paper, we obtain the sharp estimate of the first positive eigenvalue for the beam equation <span><span><span><math><mrow><msup><mrow><mi>y</mi></mrow><mrow><mrow><mo>(</mo><mn>4</mn><mo>)</mo></mrow></mrow></msup><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mo>=</mo><mo>−</mo><mi>λ</mi><mi>m</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mi>y</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></math></span></span></span>with Lidstone boundary condition, where weight function <span><math><mi>m</mi></math></span> is allowed to change sign. We first establish a variational characterization for the first positive eigenvalue of the measure differential equation (MDE) <span><span><span><math><mrow><mi>d</mi><msup><mrow><mi>y</mi></mrow><mrow><mrow><mo>(</mo><mn>3</mn><mo>)</mo></mrow></mrow></msup><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mo>=</mo><mo>−</mo><mi>λ</mi><mi>y</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mi>d</mi><mi>μ</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mo>,</mo></mrow></math></span></span></span>and solve the corresponding minimization problem of the first positive eigenvalue for the MDE, where <span><math><mi>μ</mi></math></span> is a suitable measure. Then by finding the relationship between minimization problem for the first positive eigenvalue of ordinary differential equation (ODE) and that of MDE, we obtain the explicit sharp lower bound of the first positive eigenvalue for the indefinite beam equation.</div></div>","PeriodicalId":49749,"journal":{"name":"Nonlinear Analysis-Theory Methods & Applications","volume":"262 ","pages":"Article 113933"},"PeriodicalIF":1.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145048352","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-08-20DOI: 10.1016/j.na.2025.113923
Pablo Ochoa , Ariel Salort
In this article we study different extensions of the celebrated Hopf’s boundary lemma within the context of a family of nonlocal, nonlinear and nonstandard growth operators. More precisely, we examine the behavior of solutions of the fractional -Laplacian operator near the boundary of a domain satisfying the interior ball condition. Our approach addresses problems involving both constant-sign and sign-changing potentials.
{"title":"Hopf’s lemmas and boundary behavior of solutions to the fractional Laplacian in Orlicz-Sobolev spaces","authors":"Pablo Ochoa , Ariel Salort","doi":"10.1016/j.na.2025.113923","DOIUrl":"10.1016/j.na.2025.113923","url":null,"abstract":"<div><div>In this article we study different extensions of the celebrated Hopf’s boundary lemma within the context of a family of nonlocal, nonlinear and nonstandard growth operators. More precisely, we examine the behavior of solutions of the fractional <span><math><mi>a</mi></math></span>-Laplacian operator near the boundary of a domain satisfying the interior ball condition. Our approach addresses problems involving both constant-sign and sign-changing potentials.</div></div>","PeriodicalId":49749,"journal":{"name":"Nonlinear Analysis-Theory Methods & Applications","volume":"262 ","pages":"Article 113923"},"PeriodicalIF":1.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144865185","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-09-24DOI: 10.1016/j.na.2025.113949
Pierre Aime Feulefack , Emmanuel Wend-Benedo Zongo
In this paper, we investigate on a bounded open set of with smooth boundary, an eigenvalue problem involving a sum of nonlocal operators with , and subject to the corresponding homogeneous nonlocal -Neumann boundary condition. A careful analysis of the considered problem leads us to a complete description of the set of eigenvalues as being the precise interval , where is the first nonzero eigenvalue of the homogeneous fractional -Laplacian under nonlocal -Neumann boundary condition. Due to the nonlocal feature of the operators appearing in the equations, some purely nonlocal situations occur and bring in a difference in the study of nonlocal problems compared to local ones. Furthermore, we establish that every eigenfunctions is globally bounded.
{"title":"Eigenvalues of nonlinear (p,q)-fractional Laplace operator under nonlocal Neumann conditions","authors":"Pierre Aime Feulefack , Emmanuel Wend-Benedo Zongo","doi":"10.1016/j.na.2025.113949","DOIUrl":"10.1016/j.na.2025.113949","url":null,"abstract":"<div><div>In this paper, we investigate on a bounded open set of <span><math><msup><mrow><mi>R</mi></mrow><mrow><mi>N</mi></mrow></msup></math></span> with smooth boundary, an eigenvalue problem involving a sum of nonlocal operators <span><math><mrow><msubsup><mrow><mrow><mo>(</mo><mo>−</mo><mi>Δ</mi><mo>)</mo></mrow></mrow><mrow><mi>p</mi></mrow><mrow><msub><mrow><mi>s</mi></mrow><mrow><mn>1</mn></mrow></msub></mrow></msubsup><mo>+</mo><msubsup><mrow><mrow><mo>(</mo><mo>−</mo><mi>Δ</mi><mo>)</mo></mrow></mrow><mrow><mi>q</mi></mrow><mrow><msub><mrow><mi>s</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></msubsup></mrow></math></span> with <span><math><mrow><msub><mrow><mi>s</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><msub><mrow><mi>s</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>∈</mo><mrow><mo>(</mo><mn>0</mn><mo>,</mo><mn>1</mn><mo>)</mo></mrow></mrow></math></span>, <span><math><mrow><mi>p</mi><mo>,</mo><mi>q</mi><mo>∈</mo><mrow><mo>(</mo><mn>1</mn><mo>,</mo><mi>∞</mi><mo>)</mo></mrow></mrow></math></span> and subject to the corresponding homogeneous nonlocal <span><math><mrow><mo>(</mo><mi>p</mi><mo>,</mo><mi>q</mi><mo>)</mo></mrow></math></span>-Neumann boundary condition. A careful analysis of the considered problem leads us to a complete description of the set of eigenvalues as being the precise interval <span><math><mrow><mrow><mo>{</mo><mn>0</mn><mo>}</mo></mrow><mo>∪</mo><mrow><mo>(</mo><msub><mrow><mi>λ</mi></mrow><mrow><mn>1</mn></mrow></msub><mrow><mo>(</mo><msub><mrow><mi>s</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>,</mo><mi>q</mi><mo>)</mo></mrow><mo>,</mo><mi>∞</mi><mo>)</mo></mrow></mrow></math></span>, where <span><math><mrow><msub><mrow><mi>λ</mi></mrow><mrow><mn>1</mn></mrow></msub><mrow><mo>(</mo><msub><mrow><mi>s</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>,</mo><mi>q</mi><mo>)</mo></mrow></mrow></math></span> is the first nonzero eigenvalue of the homogeneous fractional <span><math><mi>q</mi></math></span>-Laplacian under nonlocal <span><math><mi>q</mi></math></span>-Neumann boundary condition. Due to the nonlocal feature of the operators appearing in the equations, some purely nonlocal situations occur and bring in a difference in the study of nonlocal problems compared to local ones. Furthermore, we establish that every eigenfunctions is globally bounded.</div></div>","PeriodicalId":49749,"journal":{"name":"Nonlinear Analysis-Theory Methods & Applications","volume":"262 ","pages":"Article 113949"},"PeriodicalIF":1.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145157796","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-08-06DOI: 10.1016/j.na.2025.113902
Wenyong Huang , Valery G. Romanovski , Xiang Zhang
This paper provides some criteria to characterize convergence of normalizations which transform partially integrable analytic differential systems to their Poincaré–Dulac normal forms. For a family of four-dimensional partially integrable differential systems near an equilibrium which has one pair of conjugate imaginary eigenvalues and a pair of resonant nonzero real eigenvalues, we prove convergence of their normalizations. For analytic differential systems with dimension larger than 4, we illustrate that partial integrability may not be sufficient to ensure convergence of the normalizations even though Bruno’s condition holds. This work generalizes in a natural way the classical results by Poincaré and Lyapunov for a monodromic equilibrium, as well as the one by Moser for a hyperbolic saddle of analytic Hamiltonian systems of one degree of freedom.
{"title":"Convergence of normalizations for partially integrable differential systems","authors":"Wenyong Huang , Valery G. Romanovski , Xiang Zhang","doi":"10.1016/j.na.2025.113902","DOIUrl":"10.1016/j.na.2025.113902","url":null,"abstract":"<div><div>This paper provides some criteria to characterize convergence of normalizations which transform partially integrable analytic differential systems to their Poincaré–Dulac normal forms. For a family of four-dimensional partially integrable differential systems near an equilibrium which has one pair of conjugate imaginary eigenvalues and a pair of resonant nonzero real eigenvalues, we prove convergence of their normalizations. For analytic differential systems with dimension larger than 4, we illustrate that partial integrability may not be sufficient to ensure convergence of the normalizations even though Bruno’s condition <span><math><mi>ω</mi></math></span> holds. This work generalizes in a natural way the classical results by Poincaré and Lyapunov for a monodromic equilibrium, as well as the one by Moser for a hyperbolic saddle of analytic Hamiltonian systems of one degree of freedom.</div></div>","PeriodicalId":49749,"journal":{"name":"Nonlinear Analysis-Theory Methods & Applications","volume":"262 ","pages":"Article 113902"},"PeriodicalIF":1.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144779749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-09-03DOI: 10.1016/j.na.2025.113937
Niklas Knobel
This article considers the ideal 2D magnetohydrodynamic equations in a infinite periodic channel close to a combination of an affine shear flow, called Couette flow, and a constant magnetic field. This incorporates important physical effects, including mixing and coupling of velocity and magnetic field. We establish the existence and stability of the velocity and magnetic field for Gevrey-class perturbations of size , valid up to times . Additionally, the vorticity and current grow as and there is no inviscid damping of the velocity and magnetic field. This is similar to the above threshold case for the Navier–Stokes (Jacob Bedrossian et al., 2022) where growth in ‘streaks’ leads to time scales of . In particular, for the ideal MHD equations, our article suggests that for a wide range of initial data, the scenario “induction by shear vorticity and current growth vorticity and current breakdown” leads to instability and possible turbulences.
本文考虑了无限周期通道中的理想二维磁流体动力学方程,该通道接近仿射剪切流(称为Couette流)和恒定磁场的组合。这包含了重要的物理效应,包括速度和磁场的混合和耦合。我们建立了大小为i的gevrey类扰动的速度和磁场的存在性和稳定性,有效到t ~ i−1次。此外,涡度和电流以O(t)增长,并且速度和磁场没有无粘阻尼。这类似于上述三维Navier-Stokes的阈值情况(Jacob Bedrossian et al., 2022),其中“条纹”的增长导致时间尺度为t ~ ε−1。特别是,对于理想的MHD方程,我们的文章表明,对于大范围的初始数据,“剪切诱导⇒涡度和电流增长⇒涡度和电流击穿”的情况会导致不稳定和可能的湍流。
{"title":"Ideal magnetohydrodynamics around couette flow: Long time stability and vorticity–current instability","authors":"Niklas Knobel","doi":"10.1016/j.na.2025.113937","DOIUrl":"10.1016/j.na.2025.113937","url":null,"abstract":"<div><div>This article considers the ideal 2D magnetohydrodynamic equations in a infinite periodic channel close to a combination of an affine shear flow, called Couette flow, and a constant magnetic field. This incorporates important physical effects, including mixing and coupling of velocity and magnetic field. We establish the existence and stability of the velocity and magnetic field for Gevrey-class perturbations of size <span><math><mi>ɛ</mi></math></span>, valid up to times <span><math><mrow><mi>t</mi><mo>∼</mo><msup><mrow><mi>ɛ</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math></span>. Additionally, the vorticity and current grow as <span><math><mrow><mi>O</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></math></span> and there is no inviscid damping of the velocity and magnetic field. This is similar to the above threshold case for the <span><math><mrow><mn>3</mn><mi>D</mi></mrow></math></span> Navier–Stokes (Jacob Bedrossian et al., 2022) where growth in ‘streaks’ leads to time scales of <span><math><mrow><mi>t</mi><mo>∼</mo><msup><mrow><mi>ɛ</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math></span>. In particular, for the ideal MHD equations, our article suggests that for a wide range of initial data, the scenario “induction by shear <span><math><mo>⇒</mo></math></span> vorticity and current growth <span><math><mo>⇒</mo></math></span> vorticity and current breakdown” leads to instability and possible turbulences.</div></div>","PeriodicalId":49749,"journal":{"name":"Nonlinear Analysis-Theory Methods & Applications","volume":"262 ","pages":"Article 113937"},"PeriodicalIF":1.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144932827","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-01Epub Date: 2025-08-14DOI: 10.1016/j.na.2025.113916
Qingdong Guo , Ji Li , Brett D. Wick
In this paper, we establish the Fefferman–Stein type decomposition of the space in the Dunkl setting. That is if and only if where and , , represent the Dunkl–Riesz transforms. Our main tool is to characterize via two approximations, which are new even for the classical space . As a direct application of our characterization of , we prove the duality of with .
{"title":"Fefferman–Stein type decomposition of CMO spaces in the Dunkl setting and an application","authors":"Qingdong Guo , Ji Li , Brett D. Wick","doi":"10.1016/j.na.2025.113916","DOIUrl":"10.1016/j.na.2025.113916","url":null,"abstract":"<div><div>In this paper, we establish the Fefferman–Stein type decomposition of the <span><math><mi>CMO</mi></math></span> space in the Dunkl setting. That is <span><math><mrow><mi>f</mi><mo>∈</mo><mi>CMO</mi><mrow><mo>(</mo><msup><mrow><mi>R</mi></mrow><mrow><mi>d</mi></mrow></msup><mo>,</mo><mi>d</mi><mi>ω</mi><mo>)</mo></mrow></mrow></math></span> if and only if <span><span><span><math><mrow><mi>f</mi><mo>=</mo><msub><mrow><mi>f</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>+</mo><munderover><mrow><mo>∑</mo></mrow><mrow><mi>j</mi><mo>=</mo><mn>1</mn></mrow><mrow><mi>d</mi></mrow></munderover><msub><mrow><mover><mrow><mi>R</mi></mrow><mrow><mo>˜</mo></mrow></mover></mrow><mrow><mi>j</mi></mrow></msub><msub><mrow><mi>f</mi></mrow><mrow><mi>j</mi></mrow></msub><mo>,</mo></mrow></math></span></span></span>where <span><math><mrow><msub><mrow><mi>f</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>,</mo><msub><mrow><mi>f</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><mo>…</mo><mo>,</mo><msub><mrow><mi>f</mi></mrow><mrow><mi>d</mi></mrow></msub><mo>∈</mo><msub><mrow><mi>C</mi></mrow><mrow><mn>0</mn></mrow></msub><mrow><mo>(</mo><msup><mrow><mi>R</mi></mrow><mrow><mi>d</mi></mrow></msup><mo>)</mo></mrow></mrow></math></span> and <span><math><msub><mrow><mover><mrow><mi>R</mi></mrow><mrow><mo>˜</mo></mrow></mover></mrow><mrow><mi>j</mi></mrow></msub></math></span>, <span><math><mrow><mi>j</mi><mo>=</mo><mn>0</mn><mo>,</mo><mn>1</mn><mo>,</mo><mo>…</mo><mo>,</mo><mi>d</mi></mrow></math></span>, represent the Dunkl–Riesz transforms. Our main tool is to characterize <span><math><mrow><mi>CMO</mi><mrow><mo>(</mo><msup><mrow><mi>R</mi></mrow><mrow><mi>d</mi></mrow></msup><mo>,</mo><mi>d</mi><mi>ω</mi><mo>)</mo></mrow></mrow></math></span> via two approximations, which are new even for the classical space <span><math><mrow><mi>CMO</mi><mrow><mo>(</mo><msup><mrow><mi>R</mi></mrow><mrow><mi>d</mi></mrow></msup><mo>)</mo></mrow></mrow></math></span>. As a direct application of our characterization of <span><math><mrow><mi>CMO</mi><mrow><mo>(</mo><msup><mrow><mi>R</mi></mrow><mrow><mi>d</mi></mrow></msup><mo>,</mo><mi>d</mi><mi>ω</mi><mo>)</mo></mrow></mrow></math></span>, we prove the duality of <span><math><mrow><mi>CMO</mi><mrow><mo>(</mo><msup><mrow><mi>R</mi></mrow><mrow><mi>d</mi></mrow></msup><mo>,</mo><mi>d</mi><mi>ω</mi><mo>)</mo></mrow></mrow></math></span> with <span><math><mrow><msup><mrow><mi>H</mi></mrow><mrow><mn>1</mn></mrow></msup><mrow><mo>(</mo><msup><mrow><mi>R</mi></mrow><mrow><mi>d</mi></mrow></msup><mo>,</mo><mi>d</mi><mi>ω</mi><mo>)</mo></mrow></mrow></math></span>.</div></div>","PeriodicalId":49749,"journal":{"name":"Nonlinear Analysis-Theory Methods & Applications","volume":"262 ","pages":"Article 113916"},"PeriodicalIF":1.3,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144829845","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}