A Laser Ion Source for the Alphatrap Experiment

The Penning-trap experiment Alphatrap, where the first single in-trap produced ions could be observed recently, is located at the Max-Plack-Institut für Kernphysik in Heidelberg. Alphatrap is a follow-up to the Mainz g-factor experiment with the aim to measure the g-factor of the bound electron in heavy ions up to hydrogenlike 208Pb81+. These ions are externally produced and will be injected into the trap via an ultra-high vacuum beamline. To increase the precision of the future measurements, sympathetic laser cooling via 9Be+ ions is to be implemented into the setup. This will remove temperature as one of the main limitations of current measurement precision as well as allowing completely new measurement schemes by cooling to the few mK range. The production of beryllium ions requires a dedicated ion source. For this purpose, a laser ion source (LIS) was designed, built and tested in the context of this thesis and will be implemented in the existing beamline. The LIS has shown to successfully produce and allow an extraction of about 3 × 107 9Be+ ions per laser pulse. The yield and the beam quality of the produced ions fulfills the required conditions of the Alphatrap experiment

Direct Bound-Electron g-Factor Difference Measurement of Coupled Ions at Alphatrap

The Alphatrap experiment is a cryogenic Penning-trap setup with the main objective to determine the g factor of the electron bound to heavy nuclei. Within this thesis, the results of several such measurements are presented. Among these, the measurement of the g factor of 20Ne9¸ exhibits a 3σ discrepancy between theory and experimental value, which has been attributed to the required input parameter of the atomic mass of 20Ne. An independent measurement has recently confirmed the deviation of the mass, fully resolving the discrepancy. Furthermore, a measurement of 22Ne9¸ can be used to improve the precision of the atomic mass of 22Ne by a factor 8 compared to the literature value, when using the theoretically predicted g factor as an input. However, the main focus of this thesis is the development of a novel technique, which, based upon the coupling of two ions as an ion crystal, enables the most precise determination of a g-factor difference to date. This difference, determined for the isotopes 20Ne9¸ and 22Ne9¸ with a relative precision of 5.6 x 10-13 with respect to the g factor, improves the precision for isotopic shifts of g factors by about two orders of magnitude. Based upon the agreement with theory, the quantum electrodynamic contribution to the nuclear recoil can be confirmed. Alternatively, the result can be applied to improve the precision of the charge radius difference of the isotopes by about one order of magnitude or to constrain new physics by limiting a potential fifth-force of the Higgs-portal mechanism

Differential effect of a distractor on primary saccades and perceptual localization

AbstractA distractor presented nearby the target of a goal-directed short latency saccade leads to spatial averaging, that is, the saccade lands between the target and the distractor. This so-called global effect is a characteristic feature of the spatial processing underlying the programming of saccadic eye movements. To determine whether this effect of near distractors on saccade metrics is also reflected in perceptual localization, subjects performed a saccade task and a perceptual localization task using identical, briefly flashed visual stimuli. To make the available visual processing time for saccades and perception more similar, we followed the target with a mask.Without the mask, primary saccades with short latency landed between target and distractor. The distractor had less effect on primary saccades with longer latencies (>200 ms) and did not affect the final eye position after late secondary saccades in the dark. This indicates that the oculomotor system can correctly use information about the target location 200 ms after the target flash even if no visual stimulus is present during this period. Likewise the presence of a distractor did not affect perceptual localization.Under the masking condition a similar global effect occurred for primary saccades with short latencies, but the latency dependence of the global effect was weakened. Secondary saccades and perceptual localization still did not show a global effect. The results suggest that the primary saccade is based on a specific target acquisition process that differs from that used for spatial perception and for the programming of memory-guided corrective saccades

Big Data and Workplace Micro-Behaviours: A closer inspection of the social behaviour of eating and interacting

Evidence-based design aims to understand human behaviour so that strategic decisions are well-informed when creating a new space. Workplace research to date has provided interesting insights, but has mostly done so on a case-by-case basis. This approach does not yield generalisable patterns, making results problematic to use in an evidence-based design context. This paper builds upon previous large-scale analysis done by the authors and focuses on two aspects of workplace behaviour – eating and interacting. We aim to understand the nuances of these behaviours, thus we explore them as independent phenomena, separate them into subcategories and set out to understand the reasons behind these observations. The examined dataset includes 23 organisations in the UK, with a wide variety of sizes, numbers of floors and buildings. It consists of human activity data collected through direct observation, Visibility Graph Analysis and organisational parameters such as industry and flexibility of desk occupancy. The first behaviour we focus on – interaction – has already been explored in previous research and has been found to happen primarily in workspace and meeting rooms. In this instance we initially classify interactions according to the activity of the members and the type of space they occur in. The analysis of the second behaviour – eating – revolves around the activities and locations of people at lunchtime. We aim to discover where people choose to eat and how this is affected by the characteristics and availability of eating spaces. For the two behaviours studied, we examine how each activity relates to the space it is happening in, taking into account a set of spatial and organisational factors. In the first case we test each interaction against proximity to circulation and local visibility of the space, while in the second we examine the popularity of different types of spaces, for example canteens and breakout spaces, against their proximity to workspace and what possibilities of inter-visibility they offer. This paper provides detailed insights into the phenomena of interacting and eating, and reflects on limitations of traditional statistical analysis. It will also highlight further opportunities for handling these types of big datasets using different techniques such as Principal Component Analysis and machine learning

Noise Induced Complexity: From Subthreshold Oscillations to Spiking in Coupled Excitable Systems

We study stochastic dynamics of an ensemble of N globally coupled excitable elements. Each element is modeled by a FitzHugh-Nagumo oscillator and is disturbed by independent Gaussian noise. In simulations of the Langevin dynamics we characterize the collective behavior of the ensemble in terms of its mean field and show that with the increase of noise the mean field displays a transition from a steady equilibrium to global oscillations and then, for sufficiently large noise, back to another equilibrium. Diverse regimes of collective dynamics ranging from periodic subthreshold oscillations to large-amplitude oscillations and chaos are observed in the course of this transition. In order to understand details and mechanisms of noise-induced dynamics we consider a thermodynamic limit $N\to\infty$ of the ensemble, and derive the cumulant expansion describing temporal evolution of the mean field fluctuations. In the Gaussian approximation this allows us to perform the bifurcation analysis; its results are in good agreement with dynamical scenarios observed in the stochastic simulations of large ensembles

Partitioning indoor space using visibility graphs: investigating user behavior in office spaces

An abstract representation of interior space is the foundation for any spatial analysis of human activity in such environments. It must capture high level concepts such as rooms, areas and corridors, but also allow for the discrete appearance of human behaviour (for example two people will not walk through the same corridor in the same way). Within the field of Space Syntax three such representations have been proposed, axial lines, convex spaces and visibility graphs. However none of these representations are both unambiguous and allow for aggregating results. Axial lines are reductions of the space into longest lines of sight and convex spaces are ”the largest and fattest convex spaces” possible. While both are meaningful abstractions, they are ambiguous and depend on the person creating them. Visibility Graphs on the other hand provide a uniform unit of analysis by dividing the space using a lattice grid into cells of equal size and connecting the cells if they are intervisible. This representation however does not allow for a meaningful aggregation of spatial human behaviour data, given its very precise nature. We propose a new representation, one which clusters adjacent cells of the visibility graph based on different metrics and thus provides both aggregatable areas and a robust method of creation. We explore how these various metrics and properties of the visibility graph create different types of clusters and specifically examine connectivity and Visual Mean Depth on various types of spaces, from simple shapes, to complex multi-floor buildings. Finally, we demonstrate how this aids the analysis of human activity in indoor spaces by focusing on a large sample of observed activity in office spaces. We argue that this new representation provides a robust but also meaningful foundation for the analysis of indoor space

Collapse of Flux Tubes

The dynamics of an idealized, infinite, MIT-type flux tube is followed in time as the interior evolves from a pure gluon field to a $\overline q \ q$ plasma. We work in color U(1). $\overline q\ q$ pair formation is evaluated according to the Schwinger mechanism using the results of Brink and Pavel. The motion of the quarks toward the tube endcaps is calculated by a Boltzmann equation including collisions. The tube undergoes damped radial oscillations until the electric field settles down to zero. The electric field stabilizes the tube against pinch instabilities; when the field vanishes, the tube disintegrates into mesons. There is only one free parameter in the problem, namely the initial flux tube radius, to which the results are very sensitive. Among various quantities calculated is the mean energy of the emitted pions.Comment: 16 pages plus 12 figures. RevTex3. DOE/ER/40427-160N9

Invariant measure in hot gauge theories

We investigate properties of the invariant measure for the $A_0$ gauge field in finite temperature gauge theories both on the lattice and in the continuum theory. We have found the cancellation of the naive measure in both cases. The result is quite general and holds at any finite temperature. We demonstrate, however, that there is no cancellation at any temperature for the invariant measure contribution understood as Z(N) symmetrical distribution of gauge field configurations. The spontaneous breakdown of Z(N) global symmetry is entirely due to the potential energy term of the gluonic interaction in the effective potential. The effects of this measure on the effective action, mechanism of confinement and $A_0$ condensation are discussed.Comment: Latex file, 65.5kB, no figure

Low energy dynamics of U(1)^{N} Chern-Simons solitons

We apply the adiabatic approximation to investigate the low energy dynamics of vortices in the parity invariant double self-dual Higgs model with only mutual Chern-Simons interaction. When distances between solitons are large they are particles subject to the mutual interaction. The dual formulation of the model is derived to explain the sign of the statistical interaction. When vortices of different types pass one through another they behave like charged particles in magnetic field. They can form a bound state due to the mutual magnetic trapping. Vortices of the same type exhibit no statistical interaction. Their short range interactions are analysed. Possible quantum effects due to the finite width of vortices are discussed.Comment: keywords: vortex, vortices, anyons, fractional statistics, 20 pages in Latex, accepted for publication in Phys.Rev.D, ( the above keywords missing in the title were added

The Rarita-Schwinger Particles Under de Influence of Strong Magnetic Fields

In this work, we calculate the solutions of the Rarita-Schwinger equation with the inclusion of the eletromagnetic interaction. Our gauge and coupling prescription choices lead to Dirac-type solutions. One of the consequences of our results are the Landau level occupation of particles, quite different from the usual spin 1/2 particle system occupation numbers.Comment: 12 page