Broadcasting, Scalability, and Reconfigurability Aspects in an All-Optical Network Architecture

All-optical networks are a sound answer to the huge data traffic demand expected for the forthcoming information society. Interesting networking aspects are the broadcasting, scalability, and reconfiguration in an all-optical environment. These issues are addressed in the present article for an all-optical network called MATRIX, which is time slotted and uses packet switching. The architecture enables the all-optical interconnection of a large number of nodes with both a small number of wavelengths and wavelength continuity based on a consequent exploitation of wavelength-division multiplexing and space-division multiplexing (i.e., multiple fibers per cable are used). For an efficient use of the resources, each node is equipped with multiple transmitters and receivers, respectively. Two different broadcasting schemes are investigated. An analytical model is developed, and the corresponding simulation results are in good agreement. It is further shown how different networks of arbitrary size can be interconnected to larger all-optical network clusters, thereby providing scalability not only with respect to the number of nodes but also to the geographical extension. Finally, wavelength reassignments allow change of optical paths through the network in case of changing traffic patterns or network failures in order to best exploit the available network resources. The total number of possible configurations is determined by the theory of Latin Squares.     

Principle and Potential of Gradient Elution in Planar Chromatography

It was the intention of this paper to show some recent developments in thin layer chroma-togrphy aiming at increasing the separation efficiency by instrumental means and techniquesusing existing separation layers. Gradient elution in the normal phase is a most efficient wayto achieve this goal. Multi-dimensional separations by coupling gradient elution column liquid chromatography inthe reversed phase with AMD gradient elution in normal phase is suitable to achieve newdimensions of separation numbers. Assuming that the N numbers reported for HPLC translateinto separation numbers near 100, by coupling the two kinds of chromatography, separationnumbers around 500 become practically usable.     

New isotope227Rn and revised halflives for223Rn and226Rn

Neutron-rich isotopes of radon, produced by spallation reactions in a ThC² target and selected chemically, were mass-separated and used as samples for radiation counting experiments. Assignments of the activities to radon isotopes were confirmed by genetic relationships to the previously known francium daughters. The halflife for the new isotope²²⁷Rn is 23±1 s and that for²²⁶Rn is 7.4±0.1 min. X-rays,γ-rays, and conversion electrons from the²²³Rn activity were measured. The decay patterns ofK X-rays and known gamma transitions in the²²³Fr daughter yield a halflife of 23.2± 0.4 min for²²³Rn, in contrast to the value of 43± 5 min reported earlier. Energies, intensities, and likely multipolarities for the most prominent gamma transitions in the²²³Rn→²²³Fr decay are presented.     

Chemisorption of isolated Br atoms on Si(100)-(2 × 1) studied by PAC

Chemisorption and desorption of isolated bromine adatoms on the Si(100)-(2 × 1) surface were investigated with nuclear methods. Br adsorption sites at low coverages of 10⁻³ monolayers (ML) were characterised by measuring the nuclear quadrupole interaction with perturbed γγ-angular correlation (PAC) of ⁷⁷Br→⁷⁷Se probe atoms. Below room temperature, two distinct adsorption sites for Br are revealed by PAC. One of them disappears after isochronal annealing above 300 K. The more stable probe-atom state is associated with single Br atoms saturating a dangling bond of the surface, while the less stable state is attributed to adsorption of Br at a bridge site. The potential barrier between the two adsorption sites is estimated to be 0.9(1) eV. At temperatures above 550 K, the fraction of atoms on distinct sites decreases, presumably due to surface diffusion. By measuring the γ-activity of the sample, complete desorption of the ⁷⁷Br atoms was observed above 620 K.