Highly charged ions: optical clocks and applications in fundamental physics

Recent developments in frequency metrology and optical clocks have been based on electronic transitions in atoms and singly charged ions as references. These systems have enabled relative frequency uncertainties at a level of a few parts in $10^{-18}$. This accomplishment not only allows for extremely accurate time and frequency measurements, but also to probe our understanding of fundamental physics, such as variation of fundamental constants, violation of the local Lorentz invariance, and forces beyond the Standard Model of Physics. In addition, novel clocks are driving the development of sophisticated technical applications. Crucial for applications of clocks in fundamental physics are a high sensitivity to effects beyond the Standard Model and Einstein's Theory of Relativity and a small frequency uncertainty of the clock. Highly charged ions offer both. They have been proposed as highly accurate clocks, since they possess optical transitions which can be extremely narrow and less sensitive to external perturbations compared to current atomic clock species. The selection of highly charged ions in different charge states offers narrow transitions that are among the most sensitive ones for a change in the fine-structure constant and the electron-to-proton mass ratio, as well as other new physics effects. Recent advances in trapping and sympathetic cooling of highly charged ions will in the future enable high accuracy optical spectroscopy. Progress in calculating the properties of selected highly charged ions has allowed the evaluation of systematic shifts and the prediction of the sensitivity to the "new physics" effects. This article reviews the current status of theory and experiment in the field.Comment: 53 pages, 16 figures, submitted to RM

In-vivo single-cell fluorescence and size-scaling of phytoplankton chlorophyll content

In unicellular phytoplankton, the size scaling exponent of chlorophyll content per cell decreases with increasing light limitation. Empirical studies have ex- plored this allometry by combining data from several species, using average values of pigment content and cell size for each species. The resulting allometry thus in- cludes phylogenetic and size scaling effects. The possibility of measuring single-cell fluorescence with imaging-in-flow cytometry devices allows the study of the size scaling of chlorophyll content at both the inter- and intraspecific levels. In this work, the changing allometry of chlorophyll content was estimated for the first time for single phytoplankton populations by using data from a series of incubations with monocultures exposed to different light levels. Interspecifically, our experiments con- firm previous modeling and experimental results of increasing size scaling exponents with increasing irradiance. A similar pattern was observed intraspecifically but with a larger variability in size scaling exponents. Our results show that size-based pro- cesses and geometrical approaches explain variations in chlorophyll content. We also show that the single-cell fluorescence measurements provided by imaging-in-flow devices can be applied to field samples to understand the changes in the size de- pendence of chlorophyll content in response to environmental variables affecting primary production

Fuzzy Grammaticality Models: A Tool for Web Language Analysis

AbstractIn this paper, we highlight the need to propose formal models that consider grammaticality as a gradient property instead of the categorical view of grammaticality defended in theoretical linguistics. Given that deviations from the norm are inherent to the spontaneous use of language, linguistic analysis tools should account for different levels of grammaticality. Fuzzy grammaticality models may be a way to solve the problem that the so-called “noisy text” poses to parsing mechanisms used in Web language analysis–especially social networks language

Plans for laser spectroscopy of trapped cold hydrogen-like HCI

Laser spectroscopy studies are being prepared to measure the 1s ground state hyperfine splitting in trapped cold highly charged ions. The purpose of such experiments is to test quantum electrodynamics in the strong electric field regime. These experiments form part of the HITRAP project at GSI. A brief review of the planned experiments is presented.Comment: 4 pages, 4 figures, accepted for publication (NIMB

Plans for laser spectroscopy of trapped cold hydrogen-like HCI

Laser spectroscopy studies are being prepared to measure the 1s ground state hyperfine splitting in trapped cold highly charged ions. The purpose of such experiments is to test quantum electrodynamics in the strong electric field regime. These experiments form part of the HITRAP project at GSI. A brief review of the planned experiments is presented.Comment: 4 pages, 4 figures, accepted for publication (NIMB

Plans for laser spectroscopy of trapped cold hydrogen-like HCI

Laser spectroscopy studies are being prepared to measure the 1s ground state hyperfine splitting in trapped cold highly charged ions. The purpose of such experiments is to test quantum electrodynamics in the strong electric field regime. These experiments form part of the HITRAP project at GSI. A brief review of the planned experiments is presented.Comment: 4 pages, 4 figures, accepted for publication (NIMB

Nuclear-polarization effect to the hyperfine structure in heavy multicharged ions

We have investigated the correction to the hyperfine structure of heavy multicharged ions, which is connected with the nuclear-polarization effect caused by the unpaired bound electron. Numerical calculations are performed for hydrogenlike ions taking into account the dominant collective nuclear excitations. The correction defines the ultimate limit of precision in accurate theoretical predictions of the hyperfine-structure splittings

Analítica de aprendizaje en MOOC mediante métricas dinámicas en tiempo real

Este artículo presenta el diseño y funcionamiento de una experiencia de analítica mediante una plataforma que ofrece métricas dinámicas en tiempo real denominada ?MOOC Dashboard?. La experiencia se ha desarrollado por la Universidad de Southampton y la Universidad Autónoma de Madrid y se ha aplicado al análisis del funcionamiento en los cursos MOOC de la plataforma FutureLearn. El avance de la enseñanza en entornos masivos requiere, entre otras iniciativas, del conocimiento del desempeño del estudiante con respecto al diseño más o menos interactivo que ofrecen estos cursos. La visualización de métricas de aprendizaje y de la huella del estudiante en los cursos permite dinamizar y mejorar los entornos de cursos los MOOC. A través de un enfoque descriptivo-exploratorio se analiza el curso MOOC: ?Digital Marketing: Challenges and Insights? ofrecido por la plataforma FutureLearn? y se presentan los resultados de la aplicación de métricas analíticas dinámicas en tiempo real al desempeño académico de los estudiantes