We focus on matrix semigroups (and algebras) on which rank is commutable [rank(AB) = rank(BA)]. It is shown that in a number of cases (for example, in dimensions less than 6), but not always, commutativity of rank entails permutability of rank [rank(A(1)A(2)...A(n)) = rank(A(sigma(1))A(sigma(2))... ...

A dynamical-systems model of plasma glucose concentration, andits regulation by insulin and glucagon, is described, as pertains to types 1 and2 diabetes. The hyperglycemic case is seen to be dependent only on insulinconcentration, while the hypoglycemic case requires consideration of both in-sulin a...

OBJECTIVE: To evaluate use of infrared spectroscopy for diagnosis of traumatic arthritis in horses. ANIMALS: 48 horses with traumatic arthritis and 5 clinically and radiographically normal horses. PROCEDURES: Synovial fluid samples were collected from 77 joints in 48 horses with traumatic arthritis....

A matrix M is nilpotent of index 2 if M2=0. Let V be a space of nilpotent n×n matrices of index 2 over a field k where and suppose that r is the maximum rank of any matrix in V. The object of this paper is to give an elementary proof of the fact that . We show that the inequality is sharp and const...

A (non-associative) algebra A, over a field k, is called homogeneous if its automorphism group permutes transitively the one dimensional subspaces of A. Suppose A is a nontrivial finite dimensional homogeneous algebra over an infinite field. Then we prove that x(2) = 0 for all x in A, and so xy = yx...

We study the existence of common invariant subspaces for semigroups of idempotent operators. It is known that in finite dimensions every such semigroup is simultaneously triangularizable. The question; of the existence of even one non-trivial invariant subspace is still open in infinite dimensions. ...

Profiles of selected phenolic constituents of 2 apple cultivars, Northern Spy and Ida Red, commonly used for processed products Were compared. Although chlorogenic acid was the principal phenolic in both cultivars, there were significant quantitative differences. A new solid-phase extraction (SPE) a...

This paper deals with semigroups of linear transformations which act transitively on a finite-dimensional vector space. An explicit canonical form is obtained for the semigroups which lack proper transitive left ideals. The class of such semigroups can be considered to be an extention of the class o...

It is known that the smallest complete bipartite graph which is not 3-choosable has 14 vertices. We show that the extremal configuration is unique.

The usual tight-binding (TB) approximation, employed in electronic structure calculations, is extended to include the more-distant neighbor sites than the first. In doing so, a simple power law is adopted to describe the bond and overlap contributions, which enables the energy dispersion relation to...

The following questions are studied: Under what conditions does the existence of a (nonzero) fixed point for every member of a semigroup of matrices imply a common fixed point for the entire semigroup? What is the smallest number k such that the existence of a common fixed point for every k members ...

An approximate solution of the Klein-Gordon equation for the general Hulthen-type potentials in D -dimensions within the framework of an approximation to the centrifugal term is obtained. The bound state energy eigenvalues and the normalized eigenfunctions are obtained in terms of hypergeometric pol...

By the Kuratowski-Ulam theorem, if A subset of Rn+1 = R-n x R is a Borel set which has second category intersection with every ball (i.e., is "everywhere second category"), then there is a y is an element of R such that the section A boolean AND (R-n x {y}) is everywhere second category in...