The survival of the large dimensional basic contact process

Summary We consider the d-dimensional basic contact process obtaining the limit value of the probability of survival when d+, and showing that the finite dimensional distributions of the upper invariant measure become of the product form as d+.     

Rates of convergence and optimal spectral bandwidth for long range dependence

Summary For a realization of lengthn from a covariance stationary discrete time process with spectral density which behaves like ^1–2H as 0+ for 1/2<H<1 (apart from a slowly varying factor which may be of unknown form), we consider a discrete average of the periodogram across the frequencies 2j/n,j=1,..., m, wherem andm/n0 asn. We study the rate of convergence of an analogue of the mean squared error of smooth spectral density estimates, and deduce an optimal choice ofm.     

Abschwächungen des Adjunktionsbegriffs

Generalizations of right adjointness (i.e. having a left adjoint) of a functor G:AX are studied. G is called weakly right adjoint, if for any X ObX there exists an A_X ObA and an arrow e_X:X GA_X, such that for any f:XGB there is a (not necessarily unique) morphism f:A_XB inA with (Gf)e_x=f. As weakly right adjoint functors do not have so many interesting properties, it is useful to consider weakly right adjoint functors with a certain uniqueness condition. There are three ways for doing this, first by assuming uniqueness only for special f' s, second by assuming uniquness only up to automorphisms, and third by assuming a canonical choice of f. A different way of generalizing right adjointness are the locally adjunctable functors of Kaput [5]. These weaker notions of adjointness are compared, their continuity properties are studied and the problem, when they imply right adjointness is discussed.     

Nielsensche Realisierungssätze für Seifertfaserungen

Let M be a closed aspherical manifold and A a finite subgroup of the outer automorphism group Out ₁M of ₁M. A necessary (and in many cases also sufficient) condition for realising A by the induced action of an isomorphic group of homeomorphisms of M is the existence of an extension 1₁MEA1 to the abstract kernel (A,₁M, AOut ₁M). If the center of ₁M is nontrivial, this condition need not be fulfilled ([14]). We showed in [25] however that one can always find a surjection BA of a finite group B with abelian kernel such that there exists an extension to the abstract kernel (B,₁M,BAOut₁M), and one can try to realize B instead of A. The main result of the present paper is a characterisation of all such groups B (for a given A) which can be realized by a group of homeomorphisms. The class of manifolds considered here consists of certain Seifert fiber spaces in arbitrary dimensions but the main result is purely algebraic and can be applied to other classes of manifolds, for example to flat Riemannian manifolds.     

Number of quasimodes of “bouncing-ball” type

A new two-scale expansion is proposed for eigenfunctions of bouncing-ball type and the corresponding eigenvalues of the Laplace operator with the Dirichlet condition in a domain of the plane. The eigenfunctions are concentrated in a neighborhood of a stable diameter of the domain and are numbered with two indices (p, q) where p is the number of longitudinal nodes and q the number of nodes in a direction orthogonal to the diameter. The validity of the asymptotic expansions is guaranteed for 0 q const p^–1 and >0 as p +.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 117, pp. 172–182, 1981.     

The degree of maps between certain 6-manifolds

For manifolds M,M of the form S² e⁴ e⁶ we compute the homomorphisms H_*M H_*M between homology groups which are realizable by a map F: M M.     

On Upper and Lower Almost β-continuous Multifunctions

In this paper, the authors define a multifunction F : X Y to be upper (lower) almost -continuous if F+(V) (F- (V)) is -open in X for every regular open set V of Y. They obtain some characterizations and several properties concerning upper (lower) almost -continuous multifunctions.     

On a Test Statistic for Linear Trend

Let {W(s)} _s 0 be a standard Wiener process. The supremum of the squared Euclidian norm Y (t)², of the R²-valued process Y(t)=(1/t W(t), {12/t ³ int_{0 t} s dW (s)– {3/t} W(t)), t [, 1], is the asymptotic, large sample distribution, of a test statistic for a change point detection problem, of appearance of linear trend. We determine the asymptotic behavior P {sup _t [, 1] Y(t)² > u as u , of this statistic, for a fixed (0,1), and for a moving = (u) 0 at a suitable rate as u . The statistical interest of our results lie in their use as approximate test levels.     

Isomorphisms of Steinberg groups over commutative rings

LetA andR be commutative rings, andm andn be integers3. It is proved that, if :St _m (A)St _n (R) is an isomorphism, thenm=n. Whenn4, we have: (1) Every isomorphism :St _n(A)St _n(R) induces an isomorphism:E _n (A)E _n (R), and is uniquely determined by; (2) IfSt _n (A) St _n (R) thenK _2.n (A)K _2.n (R); (3) Every isomorphismE _n (A) E _n (R) can be lifted to an isomorphismSt _n(A)St _n(R); (4)St _n(A) St _n(R) if and only ifAR. For the casen=3, ifSt ₃(A) andSt ₃(R) are respectively central extensions ofE ₃(A) andE ₃ (R), then the above (1) and (2) hold.The Project supported by National Natural Science Foundation of China     

The Flooding Time in Random Graphs

Based on our analysis of the hopcount of the shortest path between two arbitrary nodes in the class G _p (N) of random graphs, the corresponding flooding time is investigated. The flooding time T _N (p) is the minimum time needed to reach all other nodes from one node. We show that, after scaling, the flooding time T _N (p) converges in distribution to the two-fold convolution ^(2*) of the Gumbel distribution function (z)=exp (–e ^–z ), when the link density p _N satisfies Np _N /(log N)³ if N .     

Polynomial Filtrations and Lannes'' T Functor

This paper defines and studies the polynomial filtration [p_k ] of the shift functor : F , where F is the category of functors between F-vector spaces over a finite field F. The functors [p_k ] correspond to a system of functors (p_k T):U U, related to Lannes'T-functor on the category U of unstable modules over the Steenrod algebra. The main results concern the behaviour of the quotients ~ _s:=~/[p_s-1~ filtrations by ~_s-nilpotent functors are introduced and it is shown that the full subcategory of _s-nilpotent functors is thick.     

Minimax detection of a signal in ℓp metrics

The problem of the minimax detection of a signal is considered in a Gaussian white noise of intensity 0. The set of the signals represents an ellipsoid in the _p-metric with lengths of semiaxes a_k ^–1 0 as k , from which a ball of radius 0 as 0 in the _p-metric has been removed. Asymptotically minimax tests have been constructed for the cases 1 < p and asymptotically sharp estimates of the minimax efficiency have been obtained.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova Akademii Nauk SSSR, Vol. 184, pp. 152–168, 1990.     

Complex whitham deformations in problems with “integrable instability”

The focusing nonlinear Schrödinger equation with finite-density boundary conditions as |x| is considered. The asymptotic behavior of the solution ast is investigated by means of the complex theory of deformations of Whitham.Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 104, No. 3, pp. 393–419, September, 1995.     

Quasianapole Interaction of Charged Fermions

We obtain the analytic expression for the total cross section of the reaction e ^– e ⁺l ^– l ⁺ (l=,) taking possible quasianapole interaction effects into account. We find numerical restrictions on the interaction parameter value from data for the reaction e ^– e ^+–+ in the energy domain below the Z ⁰ peak.     

On the solution of a generalized Schrödinger-type equation

Lu(t)+(u,F)g(t)=f(t), tS. , ( F, g). .

---

---

The authors wish to thank Professor Yu. A. Rozanov for his help and discussions.     

Distance functional and suprema of hyperspace topologies

Let CL(X) denote the nonempty closed subsets of a metrizable space X. We show that the Vietoris topology on CL(X) is the weakest topology on CL(X) such that A - d(x, A) is continuous for each x X and each admissible metric d. We also give a concrete presentation of the analogous weak topology for uniformly equivalent metrics, and are led to consider for an admissible metric d the weakest topology on CL(X) such that the gap functional (A, B) - {d(ta, b): a A, b B} is continuous on CL(X) × CL(X).Visiting the University of Minnesota.Visiting California State University, Los Angeles.     

On depth first search strees inm-out digraphs

We consider depth first search (DFS for short) trees in a class of random digraphs: am-out model. Let _i be thei ^th vertex encountered by DFS andL(i, m, n) be the height of _i in the corresponding DFS tree. We show that ifi/n asn, then there exists a constanta(,m), to be defined later, such thatL(i, m, n)/n converges in probability toa(,m) asn. We also obtain results concerning the number of vertices and the number of leaves in a DFS tree.     

On the Cohomology Sequence in a Semiabelian Category

In a semiabelian category, a strictly exact sequence 0ABC0 of cochain complexes gives rise to the cohomology sequence ...H ⁿ(A) H ⁿ(B) H ⁿ(C) H ⁿ⁺¹ (A) .... We study conditions for exactness of the homology sequence at a given term.     

Sequences of adjoints forEns-valued functors

A complete classification of full sequences of adjoint functors arising from arbitrary functors FAEns and faithful functors FAEns, respectively, is given.     

Spatial dynamics of time periodic solutions for the Ginzburg-Landau equation

We consider the dynamics of the Ginzburg-Landau equation in a small neighborhood of a known pulse solution by studying a Poincaré map,P: _{T T} , where _T is a section which is transverse to the pulse. Due to the fact that the Ginzburg-Landau equation possesses both a rotational symmetry and a spatial symmetry, we are able to conduct a detailed analytical study of this map in neighborhoods arbitrarily close to the pulse solution. Thus, we are able to complement the work of Holmes [8], who conducted an analytical study of the Poincaré map in a punctured neighborhood of the pulse. We find that the Poincaré map contains an invariant set _itT, where is not necessarily a Cantor set of points, such thatP: is homeomorphic to a shift map on (at least) two symbols. Furthermore, we find that for eachm 1 the mapP _itm possesses a fixed point. Since is not necessarily a Cantor set, this is not immediately clear. Finally, we find that when the pulse solution is broken, for eachm1 there exist parameter values such that pulses possessingm maxima appear.On leave at the University of Utah during 1993/94. Supported by the DFG, Habilitationsstipendium Ma 1587/1-1.