where w is the length of the path W, P(G, x) is the characteristic polynomial of the graph G and G-W is the graph obtained by deletion of the path W from G. For non-alternant systems the formulas for T(W) are much more complicated and are given elsewhere1. There is a straighforward interpretation of eq 1, namely T(W) can be understood as the (additive) contribution of the path W to the bond order Prs· The case of adjacent r and s is certainly the most interesting one, because of the well known relations between Prs and bond length, -bond strength, vibrational frequency, reactivity, etc.2 In the present study we shall consider exclusively the bond orders between the adjacent centers. Then since there is always a path of length one between the adjacent centers r and s, i.e., the bond connecting the atoms r and s, eq 1 is rewritten as

The Klein paradox is one of the cornerstones in the development of quantum mechanics, and its consequences were used in various branches of physics, ranging from elementary particles to solid state. Yet its mathematical derivation is questionable in a number of steps, resulting in the wrong solution of Dirac equation. In this paper, the paradox is analysed in more detail, and its mathematical content is emphasized in order to show that in the study of extreme conditions of matter simple arguments may result in erroneous predictions.

Abstract : The Final Abstracts for the Conference, Imaging in Space and Time, 28 August 2006 - 1 September 2006. The conference included: A) Acquiring and analyzing data from space. Much of information on distant objects in space is obtained from images in various frequency domains of electromagnetic radiation. Acquiring and analysis of images was reviewed. B) Nanotechnology for manipulation of light: Future advances in fundamental and applied research are envisaged in manipulation of molecules and their conglomerates with electromagnetic radiation. Results in femto and ato second research were reviewed. There were also talks on the possible implementation on quantum computing, for the fast processing of data. C) Images of the basic structure of matter: Elementary particles are the basic elements of matter, and their structure is still somewhat of a mystery. To infer on it one has to extract information data from experiments, which is known as the inversion problem. The status of the field was reviewed.