The minimal genus problem in rational surfaces CP~2#nCP~2

There are three key ingredients in the study of the minimal genus problem for rational surfaces CP2#nCP2: the generalized adjunction formula, the action of the orthogonal group of the Lorentz space and the geometric construction. In this paper, we prove the uniqueness of the standard form (see Definition 1.1 and Theorem 1.1) of a 2-dimensional homology class under the action of the subgroup of the Lorentz orthogonal group that is realized by the diffeomorphisms of CP2#nCP2.Using the geometric construction, we determine the minimal genera of some classes (see Theorem 1.2).     

Calculating the Fundamental Group of Galois Cover of the(2, 3)-embedding of CP~1× T

As known to all,it is quite difficult to compute the fundamental group of a surface of general type.In this paper,applying Moishezon-Teicher's algorithm,we investigate the fundamental group of a special surface of general type with zero topological index,namely,the Galois cover of the(2,3)-embedding of CP~1×T.Because the full presentation of the group is very complicated,we compute its special quotient and get an interesting result about its structure.     

Addition–deletion results for the minimal degree of logarithmic derivations of hyperplane arrangements and maximal Tjurina line arrangements

Journal of Algebraic Combinatorics - We study the change of the minimal degree of a logarithmic derivation of a hyperplane arrangement under the addition or the deletion of a hyperplane and give a...     

The α-orthogonal complements of regular Dirichlet subspaces for one-dimensional Brownian motion

Roughly speaking a regular Dirichlet subspace of a Dirichlet form is a subspace which is also a regular Dirichlet form on the same state space. In particular, the domain of regular Dirichlet subspace is a closed subspace of the Hilbert space induced by the domain and α-inner product of original Dirichlet form. We investigate the orthogonal complement of regular Dirichlet subspace for one-dimensional Brownian motion in this paper. Our main results indicate that this orthogonal complement has a very close connection with theα-harmonic equation under Neumann type condition.     

The extension of the operation in the Stone-Čech compactification of semigroups

For a large class of locally compact semitopological semigroups S, the Stone-Čech compactification β S is a semigroup compactification if and only if S is either discrete or countably compact. Furthermore, for this class of semigroups which are neither discrete nor countably compact, the quotient contains a linear isometric copy of ℓ _∞. These results improve theorems by Baker and Butcher and by Dzinotyiweyi.     

The role of the Ellingsrud-Strømme construction in the classification of instantons

We review a construction of Ellingsrud-Strømme relating instantons of charge n on the ordinary projective space and theta-characteristics on a plane curve of degree n with some extra-structure.     

The topological types of some irregular Kähler surfaces

The topological type of generalized Kummer surfaces is described in terms of sphere bundles over Riemann surfaces and the complex projective plane. Explicit examples of sets of pairwise non-diffeomorphic K?hler surfaces of the same topological type are given. Received: 5 January 2000     

On the freeness of Böröczky line arrangements

Periodica Mathematica Hungarica - In the present note, we focus on the freeness and some combinatorial properties of line arrangements in the projective plane having only double and triple points....     

The classification of Kleinewillinghöfer types of 2-dimensional Laguerre planes

Aequationes mathematicae - Kleinewillinghöfer classified Laguerre planes with respect to central automorphisms. Polster and Steinke investigated 2-dimensional Laguerre planes and their...     

The Cardinal of the Set of Non-quasi-regular Elements in a Ring

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The limit set of trajectory in quasi-homogeneous system in ℝ3

In this article, we study the limit set of trajectory in three-dimensional quasi-homogeneous system. For the trajectory which is close to a singular curve, we show that either it approaches a fixed point or infinity, or it oscillates. Moreover, an oscillating example is given. The behaviour of trajectory which is near a closed orbit is also studied. At the end, we classify the integral manifolds of the system with isolated singularities.     

Tensor products of power Köthe spaces of different types

The multirectangular characteristics µ _m ^(λ,c) are applied to the isomorphic classification of tensor products of the form $ E_0 (a)\widehat \otimes E_\infty (b) $ . We single out a subclass of tensor products such that the two-rectangular characteristic µ ₂ ^(λ,c) is a complete invariant on this class.     

The Asymptotic Properties of the Extremal Rings in Space and the Proof of the Anderson's Conjecture

For n≥3,1≤p≤n-1,and 0<α<1,the ring R_n,p(a)may be described as theopen unit ball in n-space minus a closed concentric p—dimensional ball of radiusα,its modulus is denoted by modR_n,p(a).Because these rings have the importantextremal properties indicated in[1],the problem of evaluating the modulus mod-R_n,p(α)is very interesting.On this problem,much research work has been done(see[1]and[2]).In this paper,the following results are obtained.     

The analysis of the number of fixed points in the key extending algorithm of RC4

The probabilities of the state transitions of the initial value So in the S table of RC4 are described by a kind of bistochastic matrices, and then a computational formula for such bistochastic matrices is given, by which the mathematical expectation of the number of fixed points in the key extending algorithm of RC4 is obtained. As a result, a statistical weakness of the key extending algorithm of RC4 is presented.     

On the number of limit cycles in general planar piecewise linear systems of node–node types

We investigate the existence and number of limit cycles in a class of general planar piecewise linear systems constituted by two linear subsystems with node–node dynamics. Using the Liénard-like canonical form with seven parameters, some sufficient and necessary conditions for the existence of limit cycles are given by studying the fixed points of proper Poincaré maps. In particular, we prove the existence of at least two nested limit cycles and describe some parameter regions where two limit cycles exist. The main results are applied to the PWL Morris–Lecar neural model to determine the existence and stability of the limit cycles.     

The r-Stirling numbers of the first kind in terms of the Möbius function

The Ramanujan Journal - The main result of this paper is an identity expressing the r-Stirling number of the first kind as a sum involving binomial coefficients and the Möbius function of the...     

The Lyapunov-Poincaré method in the theory of periodic motions

The problem of the periodic motions of a system with a small parameter is solved. The non-rough cases, when the problem cannot be solved by a generating system obtained for a zero value of the small parameter, are investigated. Lyapunov's idea of using a new generating system which already contains the small parameter is systematically developed. Systems of general form, inverse systems and systems close to inverse are investigated.