On Surface-Symmetric Spacetimes with Collisionless and Charged Matter

Some future global properties of cosmological solutions for the Einstein–Vlasov–Maxwell system with surface symmetry are presented. Global existence is proved, the homogeneous spacetimes are future complete for causal trajectories, and the same is true for inhomogeneous plane-symmetric solutions with small initial data. In the latter case some decay properties are also obtained at late times. Similar but slightly weaker results hold for hyperbolic symmetry. Submitted: July 31, 2006. Accepted: December 20, 2006.     

Isochronous Spacetimes

Acta Applicandae Mathematicae - The possibility has been recently demonstrated to manufacture (nonrelativistic, Hamiltonian) many-body problems which feature an isochronous time evolution with an...     

关于相对拓扑

在一个集合X上以一种拓朴J形成一种拓朴空间(X,J)以后,对于X中的子集Y X,可以相对拓扑(relative topology) S={u∩Y|u∈J} 构成子空间(Y,S),同样的,可以对y∈Y,构成y在Y中的邻域系 {υ∩Y|υ是y在X中的一个邻域}     

关于依测度拓扑收敛

给出了τ-可测算子的依测度收敛的充要条件和Hilbert空间内依测度收敛的充要条件．     

On the Topology of Real Bott Manifolds

The main aim of this article is to give a necessary and sufficient condition for a real Bott manifold to admit a spin structure and further give a combinatorial characterization for the spin structure in terms of the associated acyclic digraph.     

On the Topology of the Combinatorial Flag Varieties

We prove that the simplicial complex Ω _n of chains of matroids (with respect to the ordering by the quotient relation) on n elements is shellable. This follows from a more general result on shellability of the simplicial complex of W -matroids for an arbitrary finite Coxeter group W , and generalises the well-known results by Solomon—Tits and Bj?rner on spherical buildings. Received January 16, 2000, and in revised form October 7, 2000, and April 16, 2001. Online publication December 21, 2001.     

On the Topology Induced by Mixtures of Exponentials

It is shown that if X is a real vector space of uncountable dimension then the coarsest topology on X for which the function is continuous whenever is a measure on the dual space X ^* integrating the integrands is strictly coarser than the finest locally convex topology. This is derived from an inequality relating the averages of such a 'mixture of exponentials' on the vertices and facet midpoints, respectively, of a 'generalized octahedron' in a finite-dimensional space (Lemma 1).     

On the Topology of Real Algebraic Plane Curves

We revisit the problem of computing the topology and geometry of a real algebraic plane curve. The topology is of prime interest but geometric information, such as the position of singular and critical points, is also relevant. A challenge is to compute efficiently this information for the given coordinate system even if the curve is not in generic position. Previous methods based on the cylindrical algebraic decomposition use sub-resultant sequences and computations with polynomials with algebraic coefficients. A novelty of our approach is to replace these tools by Gröbner basis computations and isolation with rational univariate representations. This has the advantage of avoiding computations with polynomials with algebraic coefficients, even in non-generic positions. Our algorithm isolates critical points in boxes and computes a decomposition of the plane by rectangular boxes. This decomposition also induces a new approach for computing an arrangement of polylines isotopic to the input curve. We also present an analysis of the complexity of our algorithm. An implementation of our algorithm demonstrates its efficiency, in particular on high-degree non-generic curves.     

On Point-finiteness in Pointfree Topology

In pointfree topology, the point-finite covers introduced by Dowker and Strauss do not behave similarly to their classical counterparts with respect to tran- sitive quasi-uniformities, contrarily to what happens with other familiar types of interior-preserving covers. The purpose of this paper is to remedy this by modifying the definition of Dowker and Strauss. We present arguments to justify that this modification turns out to be the right pointfree definition of point-finiteness. Along the way we place point-finite covers among the classes of interior-preserving and closure-preserving families of covers that are relevant for the theory of (transitive) quasi-uniformities, completing the study initiated with Ferreira and Picado, Kyungpook Math. J., 44: 415–442, 2004.     

Shock Waves in Plane Symmetric Spacetimes

We consider Einstein's equations coupled to the Euler equations in plane symmetry, with compact spatial slices and constant mean curvature time. We show that for a wide variety of equations of state and a large class of initial data, classical solutions break down in finite time. The key mathematical result is a new theorem on the breakdown of solutions of systems of balance laws. We also show that an extension of the solution is possible if the spatial derivatives of the energy density and the velocity are bounded, indicating that the breakdown is really due to the formation of shock waves.     

关于Scott开滤子拓扑的core紧性

本文讨论了那样一些ＤＣＰＯ（即定向完备偏序集）的刻划问题,它们在赋以Ｓｃｏｔｔ开滤子拓扑后,其拓扑空间的开集格是连续格。该问题也是由ＬａｗｓｏｎＪＤ。与ＭｉｓｌｏｖｅＭ．提出的一系列公开问题中的一个［１］。     

On Borel Sets in Function Spaces with the Weak Topology

It is proved that the duality map ,:(, weak)x(()*, weak*)R isnot Borel. More generally, the evaluation e:(C)(K),x KR, e(f,x) = f(x), is not Borel for any function space C(K) on a compactF-space. It is also shown that a non-coincidence of norm-Boreland weak-Borel sets in a function space does not imply thatthe duality map is non-Borel.     

On the Topology of Fibrations with Section and Free Loop Spaces

We relate the brace products of a fibration with section tothe differentials in its Serre spectral sequence. In the particularcase of free loop fibrations, we establish a link between thesedifferentials and Browder operations in the fiber. Applicationsand several calculations (for the particular cases of spheresand wedges of spheres) are given. 2000 Mathematical SubjectClassification: 55P35, 55Q15, 55R05, 55R20.     

On The Profinite Topology on a Free Group

If F is a free abstract group, its profinite topology is thecoarsest topology making F into a topological group, such thatevery group homomorphism from F into a finite group is continuous.It was shown by M. Hall Jr that every finitely generated subgroupof F is closed in that topology. Let H₁, H₂, ..., H_n be finitelygenerated subgroups of F. J.-E. Pin and C. Reutenauer have conjecturedthat the product H₁ H₂ ... H_n is a closed set in the profinitetopology of F; also, they have shown that this conjecture impliesa conjecture of J. Rhodes on finite semigroups. In this paperwe give a positive answer to the conjecture of Pin and Reutenauer.Our method is based on the theory of profinite groups actingon graphs.