Motor-driven autonomous system for controlling beamline iris diaphragm apertures.

At the collinear apparatus for laser spectroscopy and applied sciences (COALA) at TU Darmstadt, collinear laser spectroscopy is applied to perform high-precision measurements of atomic transition frequencies and high voltages in an ultra-high vacuum beamline. In such laser spectroscopy beamlines, iris diaphragms are used to reduce ion beam divergence, and to ensure a good laser and ion beam overlap. Since the system that controls the diameter of the apertures presents strong hysteresis, an automated adjustment is desirable to enhance reproducibility in the aperture settings, and to reduce the effort in performing measurements where different diameters are required, especially in alternating collinear and anti-collinear measurements. To achieve this, the Iris Mover system was designed and implemented. The Iris Mover system consists of motor-driven iris apertures which can be easily controlled by users through a computer, and which accounts for hysteresis effects. Here, we explain the design process of the Iris Mover and demonstrate and discuss its functionality.

Nuclear Charge Radii of

The first laser spectroscopic determination of the change in the nuclear charge radius for a five-electron system is reported. This is achieved by combining high-accuracy ab initio mass-shift calculations and a high-accuracy measurement of the isotope shift in the 2s^{2}2p ^{2}P_{1/2}→2s^{2}3s ^{2}S_{1/2} ground state transition in boron atoms. Accuracy is increased by orders of magnitude for the stable isotopes ^{10,11}B and the results are used to extract their difference in the mean-square charge radius ⟨r_{c}^{2}⟩^{11}-⟨r_{c}^{2}⟩^{10}=-0.49(12) fm^{2}. The result is qualitatively explained by a possible cluster structure of the boron nuclei and quantitatively used to benchmark new ab initio nuclear structure calculations using the no-core shell model and Green's function Monte Carlo approaches. These results are the foundation for a laser spectroscopic determination of the charge radius of the proton-halo candidate ^{8}B.

Precision Test of Many-Body QED in the Be+ 2p Fine Structure Doublet Using Short-Lived Isotopes.

Absolute transition frequencies of the 2s 2S{1/2}→2p2P{1/2,3/2} transitions in Be^{+} were measured for the isotopes ^{7,9-12}Be. The fine structure splitting of the 2p state and its isotope dependence are extracted and compared to results of ab initio calculations using explicitly correlated basis functions, including relativistic and quantum electrodynamics effects at the order of mα(6) and mα(7) ⁢ln α. Accuracy has been improved in both the theory and experiment by 2 orders of magnitude, and good agreement is observed. This represents one of the most accurate tests of quantum electrodynamics for many-electron systems, being insensitive to nuclear uncertainties.

Coupling an aVLSI neuromorphic vision chip to a neurotrophic model of synaptic plasticity: the development of topography.

We couple a previously studied, biologically inspired neurotrophic model of activity-dependent competitive synaptic plasticity and neuronal development to a neuromorphic retina chip. Using this system, we examine the development and refinement of a topographic mapping between an array of afferent neurons (the retinal ganglion cells) and an array of target neurons. We find that the plasticity model can indeed drive topographic refinement in the presence of afferent activity patterns generated by a real-world device. We examine the resilience of the developing system to the presence of high levels of noise by adjusting the spontaneous firing rate of the silicon neurons.