On the Linear Complexity of the Power Generator

We obtain a lower bound on the linear complexity of the powergenerator of pseudo-random numbers, which in some special cases is alsoknown as the RSA generator and as the Blum–Blum–Shubgenerator. In some very important cases this bound is essentially thebest possible. In particular, this implies that lattice reductionattacks on such generators are not feasible.     

On equilibrium in the presence of friction I

A known equilibrium rule that refers to rigid bodies possibly subject to some external constraintsK _(e), and that is essential in many cases where friction is present, is shown to give unacceptable results in some cases that can be carried out experimentally. Then the same rule is replaced by a new one which is more complex. When the bearings that carry outK _(e) are kinematically independent in a suitable sense, the new rule is proved to simplify into the old one. The afore-mentioned cases can be treated satisfactorily by means of another simple rule. However this rule is shown to be too weak to treat other (simple) cases.     

Tabulation of the number of independent components of physical tensors for the magnetic classes

Following the method of Bhagavantam and Pantulu⁸ the number of independent components of tensors up to 4th rank is derived for the magnetic classes. This method is extended by Lyubarskii¹ to cases of tensors having intrinsic symmetry. The results cover all cases of tensors lacking intrinsic symmetry as well as of tensors having the symmetries of Table II, and are in agreement with previous results.^{5, 8}     

Group classification of the generalized Emden–Fowler-type equation

We perform the Lie group classification of the Emden–Fowler-type equation xu^″+nu^′+x^νF(u)=0, which arises in several applications. These include the theory of stellar structure, the thermal behaviour of a spherical cloud of gas, isothermal gas spheres and the theory of thermionic currents. Seven cases arise for the possible extension of the principal Lie algebra, which in this case is trivial. Three new cases occur for which we have non-trivial Lie point symmetry algebra. We compare these cases with the Noether symmetry cases. Moreover, we also make comparisons with the partial Noether operators. Finally for three cases we reduce the Emden–Fowler-type equation to quadratures.     

On the “One-Dimensionality” of the Extremal for the Poincaré inequality in a square

In this paper, we analyze the conditions of the existence and nonexistence of one-dimensional local minimizers of the functions induced by the Poincaré inequality. We mainly focus on the cases of square and rectangular domains. However, other cases are also discussed. Bibliography: 2 titles.     

Amalgamations of the Painlevé Equations

We present new hierarchies of nonlinear ordinary differential equations (ODEs) that are generalizations of the Painlevé equations. These hierarchies contain the Painlevé equations as special cases. We emphasize the sixth-order ODEs. Special solutions for one of them are expressed via the general solutions of the P ₁ and P ₂ equations and special cases of the P ₃ and P ₅ equations. Four of the six Painlevé equations can be considered special cases of these sixth-order ODEs. We give linear representations for solving the Cauchy problems for the hierarchy equations using the inverse monodromy transform.     

Actions of the dipper-donkin quantization GL 2 on the clifford algebra C(l,3)

Following the method already developed for studying the actions of GL_q (2,C) on the Clifford algebra C(l,3) and its quantum invariants [1], we study the action on C(l, 3) of the quantum GL ₂ constructed by Dipper and Donkin [2]. We are able of proving that there exits only two non-equivalent cases of actions with nontrivial “perturbation” [1]. The spaces of invariants are trivial in both cases.

We also prove that each irreducible finite dimensional algebra representation of the quantum GL ₂ q^m ≠1, is one dimensional.

By studying the cases with zero “perturbation” we find that the cases with nonzero “perturbation” are the only ones with maximal possible dimension for the operator algebra ?.     

Some Generalizations of the Pinwheel Tiling

We introduce a new family of nonperiodic tilings, based on a substitution rule that generalizes the pinwheel tiling of Conway and Radin. In each tiling the tiles are similar to a single triangular prototile. In a countable number of cases, the tiles appear in a finite number of sizes and an infinite number of orientations. These tilings generally do not meet full-edge to full-edge, but can be forced through local matching rules. In a countable number of cases, the tiles appear in a finite number of orientations but an infinite number of sizes, all within a set range, while in an uncountable number of cases both the number of sizes and the number of orientations is infinite. Received April 9, 1996, and in revised form September 16, 1996.     

Replacement of Factors By Subgroups in the Factorization of Abelian Groups

In his book Abelian groups, L. Fuchs raised the question asto whether, in general, in the factorization of a finite (cyclic)abelian group one factor may always be replaced by some subgroup.The answer turned out to be negative in general, but positivein certain cases. In this paper the complete answer for cyclicgroups is given. In all previously unsolved cases, the answerturns out to be positive. It is shown that a cyclic group hasthe property that in every factorization, one factor may bereplaced by a subgroup if and only if the group has order equalto the product of a prime and a square-free integer. Certainresults are also given in non-cyclic cases. 1991 MathematicsSubject Classification 20K01.     

Metric Properties and Exceptional Sets of the Oppenheim Expansions over the Field of Laurent Series

We investigate metric properties of the polynomial digits occurring in a large class of Oppenheim expansions of Laurent series, including Lüroth, Engel, and Sylvester expansions of Laurent series and Cantor infinite products of Laurent series. The obtained results cover those for special cases of Lüroth and Engel expansions obtained by Grabner, A. Knopfmacher, and J. Knopfmacher. Our results applied in the cases of Sylvester expansions and Cantor infinite products are original. We also calculate the Hausdorff dimensions of different exceptional sets on which the above-mentioned metric properties fail to hold.     

Lie group classification of the generalized Lane–Emden equation

We carry out the Lie group classification of the generalized Lane–Emden equation xu^″+nu^′+xH(u)=0, which has many applications in mathematical physics and astrophysics. We show that the equation admits a three-dimensional equivalence Lie algebra. It is also shown that the principal Lie algebra, which in this case is trivial, has seven possible extensions. Three new cases arise for which the Lie point symmetry algebra is non-trivial. Comparison is then made of these cases with the Noether symmetry cases as well as the partial Noether operators.     

三机流水作业问题若干特殊情形的NP困难性

本文研究以加工总为目标函数的三台机器流水作业问题的特殊情形的计算复杂性,证明了下列情形为ＮＰ困难的：所有工作在第二台机器上有相同的加工时间;所有工作在第一和第三台机器上有相册的加工时间;每个工件至少有一个零工序;每个工件有一个丢失的工序。     

Comparison of Brown's and Newton's method in the monotone case

Summary In many cases when Newton's method, applied to a nonlinear sytemF(x)=0, produces a monotonically decreasing sequence of iterates, Brown's method converges monotonically, too. We compare the iterates of Brown's and Newton's method in these monotone cases with respect to the natural partial ordering. It turns out that in most of the cases arising in applications Brown's method then produces better iterates than Newton's method.     

Bounds for the infinity norm of the inverse for certain M- and H-matrices

The paper presents new two-sided bounds for the infinity norm of the inverse for the so-called PM-matrices, which form a subclass of the class of nonsingular M-matrices and contain the class of strictly diagonally dominant matrices. These bounds are shown to be monotone with respect to the underlying partitioning of the index set, and the equality cases are analyzed. Also an upper bound for the infinity norm of the inverse of a PH-matrix (whose comparison matrix is a PM-matrix) is derived. The known Ostrowski, Ahlberg–Nilson–Varah, and Mora?a bounds are shown to be special cases of the upper bound obtained.     

On the existence of positive solutions of nonlinear second order differential equations

Under suitable conditions on , the boundary value problem

has at least one positive solution. Moreover, we also apply this main result to establish several existence theorems of multiple positive solutions for some nonlinear (elliptic) differential equations.

     

Moments of the generalized hyperbolic distribution

In this paper we demonstrate a recursive method for obtaining the moments of the generalized hyperbolic distribution. The method is readily programmable for numerical evaluation of moments. For low order moments we also give an alternative derivation of the moments of the generalized hyperbolic distribution. The expressions given for these moments may be used to obtain moments for special cases such as the hyperbolic and normal inverse Gaussian distributions. Moments for limiting cases such as the skew hyperbolic t and variance gamma distributions can be found using the same approach.     

Geometry of the Welch bounds

A geometric perspective involving Grammian and frame operators is used to derive the entire family of Welch bounds. This perspective unifies a number of observations that have been made regarding tightness of the bounds and their connections to symmetric k-tensors, tight frames, homogeneous polynomials, and t-designs. In particular, a connection has been drawn between sampling of homogeneous polynomials and frames of symmetric k-tensors. It is also shown that tightness of the bounds requires tight frames. The lack of tight frames of symmetric k-tensors in many cases, however, leads to consideration of sets that come as close as possible to attaining the bounds. The geometric derivation is then extended in the setting of generalized or continuous frames. The Welch bounds for finite sets and countably infinite sets become special cases of this general setting.     

Hyperelliptic components of the moduli spaces of quadratic differentials with prescribed singularities

Moduli spaces of quadratic differentials with prescribed singularities are not necessarily connected. We describe here all cases when they have a special hyperelliptic connected component. We announce the general classification theorem: up to the four exceptional cases in low dimensional stratum, any stratum of meromorphic quadratic differentials is either connected, or has exactly two connected components. In this last case, one component is hyperelliptic, the other not.     

Some special cases of the generalized hypergeometric function q+1Fq

Some special cases of the generalized hypergeometric function _q+1F_q with rational numbers as parameters are given in tabular form. These results complement existing tables. Some analytical aspects are discussed, and a derivation is given for those cases which correct existing table entries or replace numerical values by analytic expressions.