Affine Anabelian Curves in Positive Characteristic

An investigation of morphisms that coincide topologically is used to generalize to all characteristics and partly reprove Tamagawa's theorem on the Grothendieck conjecture in anabelian geometry for affine hyperbolic curves. The theorem now deals with ₁ ^tame of curves over a finitely generated field and its effect on the sets of isomorphisms. Universal homeomorphisms are formally inverted.     

Hitchin System on Singular Curves

We study the Hitchin system on singular curves. We consider curves obtainable from the projective line by matching at several points or by inserting cusp singularities. It appears that on such singular curves, all basic ingredients of Hitchin integrable systems (moduli space of vector bundles, dualizing sheaf, Higgs field, etc.) can be explicitly described, which can be interesting in itself. Our main result is explicit formulas for the Hitchin Hamiltonians. We also show how to obtain the Hitchin integrable system on such curves by Hamiltonian reduction from a much simpler system on a finite-dimensional space. We pay special attention to a degenerate curve of genus two for which we find an analogue of the Narasimhan–Ramanan parameterization of the moduli space of SL(2) bundles as well as the explicit expressions for the symplectic structure and Hitchin-system Hamiltonians in these coordinates. We demonstrate the efficiency of our approach by rederiving the rational and trigonometric Calogero–Moser systems, which are obtained from Hitchin systems on curves with a marked point and with the respective cusp and node.     

On a Class of Integro-Differential Equations in the Singular Case

Differential Equations - We study a linear integro-differential equation with a singular differential operator in the leading part. A special generalized version of the collocation method is...     

Singular Points of Real Sextic Curves I

A complete classification of the individual types of singular points is given for irreducible real sextic curves. This classification is derived by using the computer algebra system Maple. There are 191 types of singular points for real irreducible sextic curves. We clarify that the classification is based on computing just enough of the Puiseux expansion to separate the branches. A significant portion of the proof consists of a sequence of large symbolic computations that can be done nicely using Maple.     

有关Sturm—Liouville条件下的四阶奇异边值问题正解的研究

获得如下四阶奇异边值问题{u^（4）（t）-λh（t）f（t,u（t））=0,t∈（0,1）,u（0）=u（1）=0,αu^·（0）-βu^·（0）=γu^·（1）＋δu^·（1）=0,正解的存在性定理,其中α,β,γ,δ≥0,α＋β＞0,δ＋γ＞0,ρ=αγ＋γβ＋δα＞0,参数λ＞0,h（t）∈C（0,1）and f∈（（0,1）×（0,＋∞））文中主要应用全连续算子的逼近技巧和延拓定理以及不动点指数理论．     

On Two-Dimensional Finite-Gap Potential Schroedinger and Dirac Operators with Singular Spectral Curves

We describe a wide class of two-dimensional potential Schroedinger and Dirac operators which are finite-gap at the zero energy level and whose spectral curves at this level are singular, in particular may have n-multiple points with n3.     

On the Deficiency Indices of Singular Differential Operators in the Degenerate Case

Mathematical Notes -     

Computing Numerical Singular Points of Plane Algebraic Curves

Given an irreducible plane algebraic curve of degree d ≥ 3,we compute its numerical singular points,determine their multiplicities,and count the number of distinct tangents at each to decide whether th...     

On the Existence of Positive Solution for n OrderSingular Boundary Value Problems

§１．　ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｅｘｉｓｔｅｎｃｅｆｏｒｔｈｅｂｏｕｎｄａｒｙｖａｌｕｅｐｒｏｂｌｅｍｓｈａｖｅｂｅｅｎｗｉｄｅｌｙｓｔｕｄｉｅｄｒｅｃｅｎｔｌｙ．Ｉｎｔｈｉｓｐａｐｅｒ，ｗｅｗｉｌｌｄｉｓｃｕｓｓｔｈｅＢＶＰｏｆｔｈｅｆｏｌｌｏｗｉｎｇｃｏｎｄｉｔｉｏｎｓ：ｕ（ｎ）＋ａ（ｔ）ｆ（ｕ）＝０，０＜ｔ＜１，ｕ（ｋ）（０）＝０，０ｋｎ－２（１．１）ｕ（１）＝０，　ｗｈｅｒｅ（ｈ１）ａ：（０，１）→（０，∞）ｉｓａｃｏｎｔｉｎｕｏｕｓｆｕｎｃｔｉｏｎ．（ｈ２）ｆ：［０，∞）→［…     

Curves of Genus Three in Characteristic Two

For an algebraic nonsingular nonhyperelliptic complete curve of genus three defined over a field of characteristic two we show that the number of canonical Weierstrass points is one of the following: 24, 21, 20, 18, 17, 16, 15, 12, 11, 6 or 5. In most cases, we give also an explicit equation for the curve with the given number of Weierstrass points.     

On Singular Points of Solutions of the Minimal Surface Equation on Sets of Positive Measure

It is shown that, for any compact set K ? ? ⁿ (n ? 2) of positive Lebesgue measure and any bounded domain G ? K, there exists a function in the Hölder class C^1,1(G) that is a solution of the minimal surface equation in G \ K and cannot be extended from G \ K to G as a solution of this equation.     

On the Dirichlet Problem in a Characteristic Rectangle for Fourth Order Linear Singular Hyperbolic Equations

In the rectangle D = (0,

次线性奇异Dirichlet问题的正解

利用不动点指数理论,证明了奇异Dirichlet问题正解的存在性,其中函数q允许在t=0和t=1处奇异.有关结果可应用到非线性项可变号且下方无界的情形.