Optimizing the geometry of a negative ion sputter source

In order to avoid isotope fractionating effects due to slight fluctuations in the position, direction or divergence of the emerging beam, the emittance of an AMS ion source has to be lower than the acceptance of the following beam handling system. The emittance of a negative ion sputter source is determined by the energy spread of the sputtered ions and by its extraction geometry. For various configurations of the latter, we have calculated particle trajectories. Greatly reduced aberrations are attained if the electric field close to the emitting surface is nearly uniform and only weakly focussing and if the acceleration takes place in at least two lens sections. The single acceleration gap of our Hortig-type ion source [1] has therefore been replaced by a two-stage accelerating lens. Further, the curvature of the field at the surface of the sputter target is controlled by an additional electrode.     

Evaluation of throughput and protection in optically switched metropolitan network architectures

In this study, we investigate the performance of optical packet/burst switched (OPS/OBS) architectures connected as mesh and as ring topologies for future optical metropolitan networks. Network throughput and protection to link failure under uniform traffic distribution for all nodes are investigated to evaluate the sensitivity of OPS/OBSN performance. Our data are based on analytic results and computer simulations that include a comparison between various mesh and ring topologies. We also consider detailed traffic distributions over the network links and the impact caused by failure of more or less loaded links, thus providing a method to select links that require protection, which can be very useful in network planning.     

The effects of polarization mode dispersion on 2D wavelength-hopping time spreading code routed networks

In this study, we investigate the effects of multiple access interference (MAI) and polarization mode dispersion (PMD) in 2D wavelength-hopping time spreading optical code paths. The main results show the MAI effects and PMD constraint at the outage probability. The contribution of these sources of interference is analysed to choose the better design of code parameters in order to increase the performance of networks based on optical code paths. These results could be applied to determine the parameters design in code/wavelength routed networks.     

A fast beam pulsing system for isotope ratio measurements

We describe an efficient, precise and fast beam pulsing system for accelerator mass spectrometry. Precision of isotope ratio measurements for carbon are on the order of 1%. Thus the δ¹³C values needed for radiocarbon age calculation corrections can be determined during an AMS run.     

Self-organized coordinated motion in groups of physically connected robots.

An important goal of collective robotics is the design of control systems that allow groups of robots to accomplish common tasks by coordinating without a centralized control. In this paper, we study how a group of physically assembled robots can display coherent behavior on the basis of a simple neural controller that has access only to local sensory information. This controller is synthesized through artificial evolution in a simulated environment in order to let the robots display coordinated-motion behaviors. The evolved controller proves to be robust enough to allow a smooth transfer from simulated to real robots. Additionally, it generalizes to new experimental conditions, such as different sizes/shapes of the group and/or different connection mechanisms. In all these conditions the performance of the neural controller in real robots is comparable to the one obtained in simulation.     

Improved harmonic balance implementation of Floquet analysis for nonlinear circuit simulation

We present a novel algorithm for the efficient numerical computation of the Floquet quantities (eigenvalues, direct and adjoint eigenvectors) relevant to the assessment of the stability and noise properties of nonlinear forced and autonomous circuits. The approach is entirely developed in the frequency domain by means of the application of the Harmonic Balance technique, thus avoiding lengthy time–frequency transformations which might also impair the accuracy of the calculated quantities. An improvement in the computation time around one order of magnitude is observed.     

10Be dating of the inner structure of Mn-encrustations applying the Zürich tandem accelerator

We have measured ¹⁰Be and ²³⁰Th depth profiles in Mn-nodules and crusts from the Central North Pacific (2 samples), from the South China Sea (2 samples) and from the South Pacific (1 sample). Comparison of the nuclei's ages derived via ²³⁰Th and ¹⁰Be datings and other methods (K/Ar and paleontology) shows very good agreement and proofs that distortion of ¹⁰Be and ²³⁰Th ages due to radionuclide diffusion in Mn-encrustations is negligible (< 20%).In all samples we observe a smooth exponential decrease for larger sections, suggesting constant depositional ¹⁰Be fluxes within the time resolution of 0.4 to 0.8 Ma. (resulting from the thickness of the sampled intervals). Growth rates range from 2 mm/Ma to up to 20 mm/Ma.Common to all samples is a remarkable change of growth rate accompanied by a visible change of the mineralogical inner texture, dated at 6.2 Ma. We observe slower growth rates during the last 6.2 Ma than in the previous periods. Provided that the Mn-concentration in deep water has remained constant throughout time (as supported by nearly constant trace metal/manganese ratios of the samples) the data suggest that the bottom water circulation pattern has slowed down since 6.2 Ma BP.Visible changes in the inner texture corresponding to paleooceanographic time marks such as 1.3 Ma (a presumed variation of the ice volume during Middle Pleistocene), 3.3 Ma (Glaciation of the Northern Hemisphere), and 12–14 Ma ago (maximum Glaciation of the Antarctica) strongly suggest that the growth pattern of Mn-encrustations has been influenced by the response of the oceans to the history of climatic changes.     

Evolution of hybrid WDM/OCDM technology in OBS networks with optical code and wavelength conversion

The performance of a hybrid WDM/OCDM technology is investigated under impairments of Multiple Access Interference. We employed analytical models of Optical Orthogonal Codes to evaluate the switching network resources, such as the number of optical codes carried on each wavelength. Moreover, we propose and analyze a few optical code and wavelength conversion switching architectures, in order to scale the number of codes and wavelength converters and obtain a minimum burst blocking probability. The results demonstrate that architectures comprising Sparse-Partial Optical Code Converters with Sparse-Partial Wavelength Converters provide better performance. The network resources utilization are improved with number of converters, hence reaching a better cost benefit.