The optimization of electrostatic energy selection systems for low energy electrons

Design criteria are presented which allow electrostatic energy selection systems to be optimized to give the highest currents for electron beams having a low mean energy (? 500 eV) and a small energy spread (? 30 meV). Limitations in various parts of the system are discussed and a relationship between the current delivered by the system and the energy spread is presented. Different types and sizes for the energy selectors in these systems are considered and the best results are obtained with hemispherical deflectors. The advantage of using, within reasonable limits, a large selector with small image sizes is also demonstrated.     

The graph isomorphism disease

The graph isomorphism problem—to devise a good algorithm for determining if two graphs are isomorphic—is of considerable practical importance, and is also of theoretical interest due to its relationship to the concept of NP-completeness. No efficient (i.e., polynomial-bound) algorithm for graph isomorphism is known, and it has been conjectured that no such algorithm can exist. Many papers on the subject have appeared, but progress has been slight; in fact, the intractable nature of the problem and the way that many graph theorists have been led to devote much time to it, recall those aspects of the four-color conjecture which prompted Harary to rechristen it the “four-color disease.” This paper surveys the present state of the art of isomorphism testing, discusses its relationship to NP-completeness, and indicates some of the difficulties inherent in this particularly elusive and challenging problem. A comprehensive bibliography of papers relating to the graph isomorphism problem is given.     

External reflection from dielectrics at microwave frequencies

3 cm microwave are being used to investigate the beam shifts which occur for external reflection from a planar dielectric interface. The adaptation of a planar wave theory to the microwave case has proved successful in predicting the magnitudes and direction of such shifts.     

On the construction of the self-complementary graphs on 12 nodes

We briefly describe how we compiled a catalog of all the 720 self-complementary graphs on 12 nodes. In our first attempt at this compilation one graph was inadvertently omitted. The missing graph was subsequently found by making use of a theoretical formula due to Parthasarathy and Sridharan for counting self-complementary graphs with given partitions.     

Surface barrier structure analysis using leed

Using a modified image surface potential energy barrier model we have calculated intensity profiles for Cu(001) and Ni(001) which show surface barrier resonance features. These features correlate well with experimental features suggesting that the modified image barrier is an appropriate one-dimensional phenomenological model for the real surface potential energy barrier. From the available experimental data the two parameters in the model locating the origin with respect to the top row of atoms at the surface and the height of the barrier are determined for each surface.     

Spectroscopic studies of solutions,suspensions, and precipitates of poly(1,6-di-p-toluene sulfonyloxy-2,4-hexadiyne)

Optical-absorption, fluorescence, and Raman spectra for solutions, suspensions, and precipitates of poly(1,6-di-p-toluene sulfonoxy-2,4-hexadiyne) in and from nitrobenzene, acetone, and chloroform are presented. These are interpreted in terms of the occurrence of two forms of the polymer chain; a quasicrystalline form with properties close to those of single crystal polymer and a chain-extended form occurring in solution and colloidal particles, with an absorption energy of about 2.5 eV (20,000 cm^?1). No evidence is found for the presence of very short polymer chains in partially polymerized monomer at low conversion. The relationship of these results to those for deformed single crystals is briefly discussed.     

Intra-nuclear cascading in deep inelastic scattering of 150 GeV muons in emulsion

An experimental search is presented for the existence of intra-nuclear cascading which, for small values of the Bjorken scaling variable ω, is the only mechanism of particle multiplication in the target nucleus. Our data indicate that cascading does exist as one of the effective mechanisms of particle multiplication in μ-nucleus collisions. No significant variation of the observed multiplicity with ω is observed.