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Xiuqing Duan

Publications and source records attributed to Xiuqing Duan.

6 recordsLinked to original sources

Counterexamples to GNS Conjecture 1.8

We disprove both parts of Conjecture 1.8 of Gabrielov, Novikov, and Shapiro (GNS). For the Coulomb potential, a generic rational configuration of 24 unit charges in $\mathbb{R}^3$ has at least 18 nondegenerate critical points of Morse index one but exactly 14 effective Voronoi one-cells. A separate proper-line construction has at least two nondegenerate minima but only one relatively effective zero-dimensional cell intersection. For each positive subspace dimension, product suspension gives a proper-subspace counterexample.

math-ph

Critical Points of Line Restrictions of Signed Point-Charge Potentials

Let \(α>0\) and restrict a finite inverse-power potential with arbitrary real coefficients to a line. Combine terms having the same projected centre and squared height \((a,b^2)\), delete classes whose coefficient sum is zero, and let \(m\) be the number of remaining classes. We prove the following dichotomy. If \(m=0\), exact cancellation occurs if and only if every class sum vanishes, and every ordinary point of the original domain is critical. If \(m\geq1\), there are at most \(2m-1\) critical points: when all effective heights are positive the zeros are counted with analytic multiplicity, while in the presence of effective sources on the line the assertion is one global distinct-point bound. This proves the signed line conjecture of Gabrielov--Novikov--Shapiro, valid throughout their range and in fact for every \(α>0\). The structural input is a projective paired Haar theorem: for finite \(β>1\), the full \(2m\)-dimensional space \(\sum L_j/Q_j^β\), with pairwise nonproportional positive-definite binary quadratics and arbitrary real linear numerators, has at most \(2m-1\) projective zeros counted with multiplicity. For positive charges, the substitution \(p=2α\) proves Conjecture~3 of Edelsbrunner--Fillmore--Oliveira throughout its stated range \(p\geq1\) and extends the same conclusion to every \(p>0\). For every \(n\), an explicit positive \(n\)-charge configuration attains \(2n-1\) simple critical points.

math-ph

A new family of solitons for nonlinear Schrödinger equations with non-vanishing boundary conditions in high dimension

In space dimensions $N \geq 4$, we introduce a new minimization procedure to construct traveling wave solutions to nonlinear Schrödinger equations with non-vanishing boundary conditions at spatial infinity. We denote the family of solitons obtained using this construction by $\mathscr{J}$. Mariş (Ann. of Math. 178:107-182, 2013) obtained a family of solitons by minimizing the action functional subject to a Pohozaev constraint; we use $\mathscr{P}$ to denote this family of solitons. Chiron and Mariş (Arch. Rational Mech. Anal. 226:143-242, 2017) used minimizing energy at fixed momentum to obtain a family of solitons; we denote this family of solitons by $\mathscr{Q}$. We show that, under some conditions, we have $\mathscr{Q} \subset \mathscr{J} \subset \mathscr{P}$. In addition, we show that $\mathscr{P} \subset \mathscr{J}$ under specific conditions.

math.AP

Harmonic field in knotted space

Knotted fields enrich a variety of physical phenomena, ranging from fluid flows, electromagnetic fields, to textures of ordered media. Maxwell's electrostatic equations, whose vacuum solution is mathematically known as a harmonic field, provide an ideal setting to explore the role of domain topology in determining physical fields in confined space. In this work, we show the uniqueness of a harmonic field in knotted tubes, and reduce the construction of a harmonic field to a Neumann boundary value problem. By analyzing the harmonic field in typical knotted tubes, we identify the torsion driven transition from bipolar to vortex patterns. We also analogously extend our discussion to the organization of liquid crystal textures in knotted tubes. These results further our understanding about the general role of topology in shaping a physical field in confined space, and may find applications in the control of physical fields by manipulation of surface topology.

cond-mat.soft

Proof of Atiyah-Singer Index Theorem by Canonical Quantum Mechanics

We show that the Atiyah-Singer index theorem of Dirac operator can be directly proved in the canonical formulation of quantum mechanics, without using the path-integral technique. This proof takes advantage of an algebraic isomorphism between Clifford algebra and exterior algebra in small $τ$ (high temperature) limit, together with simple properties of quantum mechanics of harmonic oscillator. Compared to the proof given by heat kernel, we try to prove this theorem more quantum mechanically.

math-ph

Curvature-driven stability of defects in nematic textures over spherical disks

Stabilizing defects in liquid-crystal systems is crucial for many physical processes and applications ranging from functionalizing liquid-crystal textures to recently reported command of chaotic behaviors of active matters. In this work, we perform analytical calculations to study the curvature driven stability mechanism of defects based on the isotropic nematic disk model that is free of any topological constraint. We show that in a growing spherical disk covering a sphere the accumulation of curvature effect can prevent typical +1 and +1/2 defects from forming boojum textures where the defects are repelled to the boundary of the disk. Our calculations reveal that the movement of the equilibrium position of the +1 defect from the boundary to the center of the spherical disk occurs in a very narrow window of the disk area, exhibiting the first-order phase-transition-like behavior. For the pair of +1/2 defects by splitting a +1 defect, we find the curvature driven alternating repulsive and attractive interactions between the two defects. With the growth of the spherical disk these two defects tend to approach and finally recombine towards a +1 defect texture. The sensitive response of defects to curvature and the curvature driven stability mechanism demonstrated in this work in nematic disk systems may have implications towards versatile control and engineering of liquid crystal textures in various applications.

cond-mat.soft