State-Selective Attachment of Helium to Molecular Ions in a New Cryogenic Ion Trap

Light is the main information about the interstellar medium accessible on Earth. Based on this information one can conclude on the composition of the region where the light originates from, as well as on its history. The requirement for this is that it is possible to identify the different absorption and emission features in the spectrum and assign them to certain molecules, atoms or ions. To enable the identification of the different species, precise spectroscopic investigations of the species in the laboratory are necessary. In this work a new spectroscopic method is presented, which can be used to record pure rotational spectra of mass selected, cold, stored molecular ions. It is based on the idea of state specific attachment of helium atoms to the stored molecular ions. The new technique has been made possible through the development and recent completion of two new 22-pole ion trap instruments in the work group of Laboratory Astrophysics at the University of Cologne. These new instruments have the advantage to reach temperatures as low as 4K compared to the 10K of the predecessor instrument. These low temperatures enable the ternary attachment of helium atoms to the stored molecular ions and by this make it possible to develop this new method for pure rotational spectroscopy. According to this, this work is divided into two parts. The first part deals with the new FELion experiment that was build and characterized in the first part of the thesis. FELion is a cryogenic 22-pole ion trap apparatus, allowing to generate, mass select, store and cool down, and analyze molecular ions. The different components of the instrument, e.g. the Storage Ion Source for generating the ions or the first quadrupole mass filter, are described and characterized in this part. Besides this also the newly developed control and data acquisitions system is introduced. With this instrument the measurements presented in the second part of the work were performed. The second part deals with the new action spectroscopic method of state-selective helium attachment to the stored molecular ions. For a deeper analysis of the new technique the systems of CD+ and helium and HCO+ and helium are investigated in detail. Analytical and numerical models of the process are presented and compared to experimental results. The results of these investigations point to a seemingly very general applicability of the new method to a wide class of molecular ions. In the final part of the thesis measurements of the rotational spectrum of l-C3H+ are presented. These measurements have to be high-lighted, since it was possible for the first time in the laboratory to unambiguously measure four low-lying rotational transitions of l-C3H+. These measurements (Brünken et al. ApJL 783, L4 (2014)) enabled the reliable identification of so far unidentified emision lines observed in several regions of the interstellar medium (Pety et al. Astron. Astrophys. 548, A68 (2012), McGuire et al. The Astrophysical Journal 774, 56 (2013) and McGuire et al. The Astrophysical Journal 783, 36 (2014)).

Development of Novel Time-Domain Electromagnetic Methods for Offshore Groundwater Studies: A Data Application from Bat Yam, Israel

Recent marine long-offset transient electromagnetic (LOTEM) measurements yielded the offshore delineation of a fresh groundwater body beneath the seafloor in the region of Bat Yam, Israel. The LOTEM application was effective in detecting this freshwater body underneath the Mediterranean Sea and allowed an estimation of its seaward extent. However, the measured data set was insufficient to understand the hydrogeological configuration and mechanism controlling the occurrence of this fresh groundwater discovery. Especially the lateral geometry of the freshwater boundary, important for the hydrogeological modelling, could not be resolved. Without such an understanding, a rational management of this unexploited groundwater reservoir is not possible. Two new high-resolution marine time-domain electromagnetic methods are theoretically developed to derive the hydrogeological structure of the western aquifer boundary. The first is called Circular Electric Dipole (CED). It is the land-based analogous of the Vertical Electric Dipole (VED), which is commonly applied to detect resistive structures in the subsurface. Although the CED shows exceptional detectability characteristics in the step-off signal towards the sub-seafloor freshwater body, an actual application was not carried out in the extent of this study. It was found that the method suffers from an insufficient signal strength to adequately delineate the resistive aquifer under realistic noise conditions. Moreover, modelling studies demonstrated that severe signal distortions are caused by the slightest geometrical inaccuracies. As a result, a successful application of CED in Israel proved to be rather doubtful. A second method called Differential Electric Dipole (DED) is developed as an alternative to the intended CED method. Compared to the conventional marine time-domain electromagnetic system that commonly applies a horizontal electric dipole transmitter, the DED is composed of two horizontal electric dipoles in an in-line configuration that share a common central electrode. Theoretically, DED has similar detectability/resolution characteristics compared to the conventional LOTEM system. However, the superior lateral resolution towards multi-dimensional resistivity structures make an application desirable. Furthermore, the method is less susceptible towards geometrical errors making an application in Israel feasible. In the extent of this thesis, the novel marine DED method is substantiated using several one-dimensional (1D) and multi-dimensional (2D/3D) modelling studies. The main emphasis lies on the application in Israel. Preliminary resistivity models are derived from the previous marine LOTEM measurement and tested for a DED application. The DED method is effective in locating the two-dimensional resistivity structure at the western aquifer boundary. Moreover, a prediction regarding the hydrogeological boundary conditions are feasible, provided a brackish water zone exists at the head of the interface. A seafloor-based DED transmitter/receiver system is designed and built at the Institute of Geophysics and Meteorology at the University of Cologne. The first DED measurements were carried out in Israel in April 2016. The acquired data set is the first of its kind. The measured data is processed and subsequently interpreted using 1D inversion. The intended aim of interpreting both step-on and step-off signals failed, due to the insufficient data quality of the latter. Yet, the 1D inversion models of the DED step-on signals clearly detect the freshwater body for receivers located close to the Israeli coast. Additionally, a lateral resistivity contrast is observable in the 1D inversion models that allow to constrain the seaward extent of this freshwater body. A large-scale 2D modelling study followed the 1D interpretation. In total, 425 600 forward calculations are conducted to find a sub-seafloor resistivity distribution that adequately explains the measured data. The results indicate that the western aquifer boundary is located at 3600 m - 3700 m before the coast. Moreover, a brackish water zone of 3 Omega*m to 5 Omega*m with a lateral extent of less than 300 m is likely located at the head of the freshwater aquifer. Based on these results, it is predicted that the sub-seafloor freshwater body is indeed open to the sea and may be vulnerable to seawater intrusion.

Diversity and Stability in Food Webs : Impacts of Non-Equilibrium Dynamics, Topology and Variation

With progressive climate change, the preservation of biodiversity is becoming increasingly important. Only if the gene pool is large enough and requirements of species are diverse, there will be species that can adapt to the changing circumstances. To maintain biodiversity, we must understand the consequences of the various strategies. Mathematical models of population dynamics could provide prognoses. However, a model that would reproduce and explain the mechanisms behind the diversity of species that we observe experimentally and in nature is still needed. A combination of theoretical models with detailed experiments is needed to test biological processes in models and compare predictions with outcomes in reality. In this thesis, several food webs are modeled and analyzed. Among others, models are formulated of laboratory experiments performed in the Zoological Institute of the University of Cologne. Numerical data of the simulations is in good agreement with the real experimental results. Via numerical simulations it can be demonstrated that few assumptions are necessary to reproduce in a model the sustained oscillations of the population size that experiments show. However, analysis indicates that species "thrown together by chance" are not very likely to survive together over long periods. Even larger food nets do not show significantly different outcomes and prove how extraordinary and complicated natural diversity is. In order to produce such a coexistence of randomly selected species—as the experiment does—models require additional information about biological processes or restrictions on the assumptions. Another explanation for the observed coexistence is a slow extinction that takes longer than the observation time. Simulated species survive a comparable period of time before they die out eventually. Interestingly, it can be stated that the same models allow the survival of several species in equilibrium and thus do not follow the so-called competitive exclusion principle. This state of equilibrium is more fragile, however, to changes in nutrient supply than the oscillating coexistence. Overall, the studies show, that having a diverse system means that population numbers are probably oscillating, and on the other hand oscillating population numbers stabilize a food web both against demographic noise as well as against changes of the habitat. Model predictions can certainly not be converted at their face value into policies for real ecosystems. But the stabilizing character of fluctuations should be considered in the regulations of animal populations.