Několik příspěvků v tomto čísle cituje dílo A. Procy v souvislosti s problémem možné nenulové hmotnosti fotonu. Ukážeme zde, že dílo tohoto francouzského teoretického fyzika rumunského původu je mnohem rozsáhlejší. Byl skutečně významným a všestranným fyzikem., In this year we commemorate 60 years since the death of Alexandru Proca, one of the greatest physicists of the 20th century. He was a French scientist of Romanian origin. He developed the vector meson theory of nuclear forces and the relativistic quantum field equations which bear his name (Proca‘s equations) for the massive, vector spin-1 mesons., Ivo Kraus., and Obsahuje seznam literatury
" ... published in conjunction with the exhibition, 'Alfred Kubin: Drawings 1897-1909,' Neue Galerie New York, September 25, 2008-January 26, 2009"--Rub tit. l. and Přeloženo z němčiny
During a two-year investigation of the Úpské rašeliniště peat bog and the Pančavské rašeliniště peat bog in the Krkonoše Mts (Czech Republic) about 228 taxa of cyanobacteria and algae were found. The diatoms were the dominant group in most of the investigated samples. The relationship between algal flora and the environmental characteristics of the pools was studied. The pH, shading and type of bed were most important factors influencing algal communities in the pools.
Let T be an infinite locally finite tree. We say that T has exactly one end, if in T any two one-way infinite paths have a common rest (infinite subpath). The paper describes the structure of such trees and tries to formalize it by algebraic means, namely by means of acyclic monounary algebras or tree semilattices. In these algebraic structures the homomorpisms and direct products are considered and investigated with the aim of showing, whether they give algebras with the required properties. At the end some further assertions on the structure of such trees are stated, without the algebraic formalization.
Let $G$ be a $k$-connected graph with $k \ge 2$. A hinge is a subset of $k$ vertices whose deletion from $G$ yields a disconnected graph. We consider the algebraic connectivity and Fiedler vectors of such graphs, paying special attention to the signs of the entries in Fiedler vectors corresponding to vertices in a hinge, and to vertices in the connected components at a hinge. The results extend those in Fiedler's papers Algebraic connectivity of graphs (1973), A property of eigenvectors of nonnegative symmetric matrices and its application to graph theory (1975), and Kirkland and Fallat's paper Perron Components and Algebraic Connectivity for Weighted Graphs (1998).