Admissibility of linear estimators of regression coefficients under quadratic loss

For the general fixed effects linear model:Y=X+, N(0,V),V0, we obtain the necessary and sufficient conditions forLY+a to be admissible for a linear estimable functionS in the class of all estimators under the loss function (d -S)D(d -S), whereD0 is known. For the general random effects linear model: =XV ₁₁ X+XV ₁₂+V ₂₁ X+V ₂₂0, we also get the necessary and sufficient conditions forLY+a to be admissible for a linear estimable functionS+Q in the class of all estimators under the loss function (d -S -Q)D(d -S -Q), whereD0 is known.     

Asymptotic behavior of maximum of an equiprobable polynomial scheme

An equiprobable polynomial scheme is considered with N outcomes and n independent trials. For n/N In N the asymptotic distribution is studied of the quantity = , where is the number of occurrences of the i-th outcome.Translated from Matematicheskie Zametki, Vol. 5, No. 3, pp. 305–316, March, 1969.     

On theq-log-concavity of Gaussian binomial coefficients

We give a combinatorial proof that is a polynomial inq with nonnegative coefficients for nonnegative integersa, b, k, l withab andlk. In particular, fora=b=n andl=k, this implies theq-log-concavity of the Gaussian binomial coefficients , which was conjectured byButler (Proc. Amer. Math. Soc. 101 (1987), 771–775).     

Quantitative recurrence results

Summary LetX be a probability measure spaceX=(X, , ) endowed with a compatible metricd so that (X,d) has a countable base. It is well-known that ifTXX is measure-preserving, then -almost all pointsxX are recurrent, i.e., . We show that, under the additional assumption that the Hausdorff -measureH (X) ofX is -finite for some >0, this result can be strengthened: , for -almost all pointsxX. A number of applications are considered.Oblatum 24-II-1992 & 8-II-1993Supported in part by NSF-DMS-9003450     

Asymptotic solution for a new class of forbiddenr-graphs

We consider the problem of finding ex (n; G), defined as the maximal number of edges anr-graph onn vertices can have that contains no subgraph isomorphic toG. We construct certainr-graphsG for which we find the coefficient(G) of the asymptotic expansion ex(n;G)== asn.     

A 2-extension of the field ℚ of rational numbersof rational numbers

It is proved that the rational number field has one, and only one, normal 2-extension (_{2, t8)}/with group isomorphic to .If is the maximal subfield of a real-closed field, which does not contain ,then the algebraic closure of is isomorphic to the field .Bibliography: 7titles.Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 236, 1997, pp. 192–196.     

On computing the number of subgroups of a finite Abelian group

We consider the numberN _A (r) of subgroups of orderp ^r ofA, whereA is a finite Abelianp-group of type =₁,₂,..., _l ()), i.e. the direct sum of cyclic groups of order ⁱⁱ. Formulas for computingN _A (r) are well known. Here we derive a recurrence relation forN _A (r), which enables us to prove a conjecture of P. E. Dyubyuk about congruences betweenN _A (r) and the Gaussian binomial coefficient .     

Hyponormality of Toeplitz Operators with Polynomial and Symmetric-Type Symbols

Suppose that is a trigonometric polynomial of the form (z) = ^N_n=-N a_n zⁿ. It is well-known that T is normal if and only if | a_{– N}| =  | a_N| and the Fourier coefficients of satisfy the following symmetry condition:

Investigations on slow versus fast growing: How to majorize slow growing functions nontrivially by fast growing ones

Let T() be the ordinal notation system from Buchholz-Schütte (1988). [The order type of the countable segmentT()₀ is — by Rathjen (1988) — the proof-theoretic ordinal the proof-theoretic ordinal ofACA ₀ + ( ₁ ^l –TR).] In particular let _a denote the enumeration function of the infinite cardinals and leta ₀ a denote the partial collapsing operation on T() which maps ordinals of T() into the countable segment T ₀ of T(). Assume that the (fast growing) extended Grzegorczyk hierarchy and the slow growing hierarchy are defined with respect to the natural system of distinguished fundamental sequences of Buchholz and Schütte (1988) in the following way:

Duality for contravariant functors on Banach spaces

The following notion of duality is studied: IfG is a contravariant functor on Ban, then . We derive the following results: The^x-reflexive functors are exactly the maximal subfunctors ofH(.,A) with reflexiveA, G ^x is^x-reflexive if and only ifG(I) is a reflexive Banach space,G ^x=(G_e)^x, andG ^x(X)=G_e(X) ifX has the metric approximation property. the last result has the consequence that for the tensor product of functors holds, ifX has the m. A. P. Dedicated to Prof. Dr. E. Hlawka on the occasion of his 60th birthday     

Concentration phenomena in weakly coupled elliptic systems with critical growth*

In this paper we consider the weakly coupled elliptic system with critical growth

Complexity of the realization of a linear function in the class of II-circuits

It is proved that the linear function gn(x₁,..., x_n) = x₁ + ... + x_nmod 2 is realized in the class of II-circuits with complexity L(g_n) n². Combination of this result with S. V. Yablonskii's upper bound yields L(g_n) n².Translated from Matematicheskie Zametki, Vol. 9, No. 1, pp. 35–40, January, 1971.     

An Upper Bound for the Cardinality of an <Emphasis Type="Italic">s</Emphasis>-Distance Set in Euclidean Space

In this paper we show that if X is an s-distance set in ^m and X is on p concentric spheres then Moreover if X is antipodal, then .     

Properties of a jointly ergodic action of the direct product of two groups

An ergodic action a of the direct product of and , not isomorphic to a product of actions of and G, is constructed, such that the actions of and G separately are not ergodic. The actions of on its ergodic components are metrically isomorphic if and only if these components are taken into one another by the action of G. Finally, the centralizerC (×G) is such thatC (×G)/(×G)₂.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 43, No. 5, pp. 684–688, May, 1991.     

A proof of Shelah's partition theorem

A self contained proof of Shelah's theorem is presented: If is a strong limit singular cardinal of uncountable cofinality and 2 > ⁺ then .     

The boundedness below of 2×2 upper triangular operator matrices

Wen and are given we denote byM _C an operator acting on the Hilbert space of the form

On construction ofk-wise independent random variables

A 0–1probability space is a probability space (, 2,P), where the sample space -{0, 1} ⁿ for somen. A probability space isk-wise independent if, whenY _i is defined to be theith coordinate or the randomn-vector, then any subset ofk of theY _i 's is (mutually) independent, and it is said to be a probability spacefor p ₁,p ₂, ...,p _n ifP[Y _i =1]=p _i .We study constructions ofk-wise independent 0–1 probability spaces in which thep _i 's are arbitrary. It was known that for anyp ₁,p ₂, ...,p _n , ak-wise independent probability space of size always exists. We prove that for somep ₁,p ₂, ...,p _n [0,1],m(n,k) is a lower bound on the size of anyk-wise independent 0–1 probability space. For each fixedk, we prove that everyk-wise independent 0–1 probability space when eachp _i =k/n has size (n _k ). For a very large degree of independence —k=[n], for >1/2- and allp _i =1/2, we prove a lower bound on the size of . We also give explicit constructions ofk-wise independent 0–1 probability spaces.This author was supported in part by NSF grant CCR 9107349.This research was supported in part by the Israel Science Foundation administered by the lsrael Academy of Science and Humanities and by a grant of the Israeli Ministry of Science and Technology.     

On One Counterexample in Convex Approximation

We prove the existence of a function fcontinuous and convex on [–1, 1] and such that, for any sequence {p _n} _{n= 1} of algebraic polynomials p _nof degree nconvex on [–1, 1], the following relation is true: , where ₄(t, f) is the fourth modulus of continuity of the function fand . We generalize this result to q-convex functions.     

Uniqueness of solutions for some nonlinear Dirichlet problems

We consider here a class of nonlinear Dirichlet problems, in a bounded domain , of the form

Asymptotic solution of a turán-type problem

LetA, B, C be disjointk-element sets. It is shown that if a 2k-graph onn vertices contains no three edges of the formA B, A C, B C then it has at most edges. Moreover, this is essentially best possible.