Gamma measurements with the 4pi BaF2 detector for the FRANZ facility
- The current performance of a 4π barium fluoride gamma detector consisting of 41 modules is evaluated. It will be used to measure neutron capture events in different samples that are exposed to a neutron beam that is expected to contain up to 10^7 neutrons/(cm^2 sec). The capture cross-sections acquired in this experiment will be relevant to a multitude of different areas, for example to s-process studies, or accelerator-driven systems. The detector array was re-mounted after having been moved from Karlsruhe to Frankfurt and in the course of this process, the detector modules have been checked for their current detection properties. Every module consists of a BaF2 crystal, a photomultiplier tube connected to the crystal by sillicon oil and a voltage divider to drive the PMT, so each of them is already an individual gamma detector. Using Cobalt-60 and Caesium-137 test sources the energy resolution and - more importantly - the time resolution of every module has been determined; the results are presented in this work and compared to previous data taken at the time the detector was built initially in the mid-1980s.
Program equivalences for concurrency abstractions in a concurrent lambda calculus with buffers, cells and futures
- Various concurrency primitives had been added to functional programming languages in different ways. In Haskell such a primitive is a MVar, joins are described in JoCaml and AliceML uses futures to provide a concurrent behaviour. Despite these concurrency libraries seem to behave well, their equivalence between each other has not been proven yet. An expressive formal system is needed. In their paper "On proving the equivalence of concurrency primitives", Jan Schwinghammer, David Sabel, Joachim Niehren, and Manfred Schmidt-Schauß define a universal calculus for concurrency primitives known as the typed lambda calculus with futures. There, equivalence of processes had been proved. An encoding of simple one-place buffers had been worked out. This bachelor’s thesis is about encoding more complex concurrency abstractions in the lambda calculus with futures and proving correctness of its operational semantics. Given the new abstractions, we will discuss program equivalence between them. Finally, we present a library written in Haskell that exposes futures and our concurrency abstractions as a proof of concept.
A solid supported membrane based electrophysiological study of the escherichia coli NhaA variant E241C
Marco Daniel Kokic
- The dependence of the Escherichia coli Na+H+ antiporter A (EcNhaA) pH sensor mutant E241C on H+ and Na+ concentrations was tested using a solid supported membrane (SSM) based electrophysiological approach. Proteoliposome preparations with right side out (RSO) oriented carriers were used to investigate the passive downhill uptake mode (physiologically the reverse transport mode) at zero membrane potential. Na+ concentration gradients established with a rapid solution exchange acted as the driving force. When a Na+ concentration gradient was established at symmetrical pH, the transport activity of the E241C EcNhaA variant was similar to that of the wildtype EcNhaA, with no shift of the bell-shaped pH dependence, an increase of the KmNa at acidic pH and a decrease of the KmNa at alkaline pH, supporting the model of a competitive binding of Na+ and H+ to a common binding site.
Non-equilibrium expansion dynamics of strongly correlated bosons in a 2d optical lattice
Systematic Time Resolution Measurements of Prototype Plastic Scintillator Bars with Photomultiplier Readout for the NeuLAND Detector
- The following thesis is the description and the analysis of time resolution measurements of the plastic scintillator protorypes bar with PMT (photomultiplier tube) readout, performed with a 31 MeV electron beam at the HZDR (Helmholtz-Zentrum Dresden-Rossendorf) . Similar bars will be used as building blocks for the NeuLAND detector (new large area neutron detector) - a ToF (time of flight) wall within the R3B setup (Reactions with Relativistic Radioactive Beams ) at the future FAIR facility (GSI Darmstadt ). The superconducting ELBE (electron linear-accellerator for beams of high brilliance and low emittance) was used as an electron source. The scintillation material used was RP408.
Two series of measurements were made within three months. In the first series, three bars of different sizes (200 x 5 x 5 cm3; 200 x 3 x 3 cm3; 300 x 5 x 5 cm3, the latter was made by coupling one 100 cm bar with a 200 cm bar using silicon grease) were used in the experiment consecutively. They had one Hamamatsu R8619 photomultiplier tube with an active diameter of 22 mm attached to each side with silicon grease. A measurement with the 200 x 5 x 5 cm3 bar without silicon grease was also performed.
In the second series, two equal scintillator bars (270 x 5 x 5 cm3 with a 10 cm light guide) on each side were used. Measurements with and without silicon coupling as well as with two different types of PMTs (R8619 and R2059) were executed.
Time and charge signals were processed with the TACQUILA electronic board. The time resolution was measured with the very precise pulsed electron signal of the accelerator. The time resolution measurements resulted in ρ200x5x5 ~ 159 ps; ρ200x5x5,no silicon ~ 162 ps; ρ200x3x3 ~ 153 ps; ρ300x5x5 ~ 204 ps.
For the second date they resulted in ρR8619 ~ 149 ps; ρR8619, no silicon ~ 175 ps; ρR2059 ~ 141 ps.
More tests and analysis is required until the results are definite.
The thermal neutron capture cross section of 60Fe
- This work derives the value of the neutron capture cross section of 60Fe at the energy of kT = 25 meV. Iron plays an important role in stellar nucleosynthesis, because it is a seed material for the s-process, a neutron capture process in which the elements between iron and bismuth are synthesized.
To determine the thermal neutron cross section of 60Fe, an iron sample produced in the framework of the ERAWAST1 program at the Paul Scherrer Institute in Switzerland was irradiated at the research reactor TRIGA2 at Johannes Gutenberg University in Mainz, Germany. Before the irradiation, the number of 60Fe particles
in the sample was calculated using the decay scheme of 60Fe. There were (8.207 ± 0:066 stat 0:298 syst) * 10 14 60Fe particles in the sample.
The irradiation of the sample took place in May 2012. The counting of the reaction product, 61Fe, was undertaken using a HPGe detector located in a laboratory at Johannes Gutenberg University in Mainz. Knowing the number of 60Fe particles in the sample, the number of produced 61Fe particles and the neutron flux from the reactor, the thermal neutron capture cross section of ρth60Fe = (0.203 ± 0:021 stat 0:024 syst) b could be determined.
The determination of the thermal neutron capture cross section at the energy of kT = 25 meV constitutes to the first at this energy. There was already a measurement of the neutron capture cross section of 60Fe at the energy of kT = 25 keV in Karlsruhe in Germany. The result of the measurement was 25 keV = (9.9 ± 2:8 syst 1:4 stat) mb and was published in the year 2009 .
Adding datapoints for the cross section at different energies improves extarpolation and helps verification of theoretical models for elemental synthesis. For this reason, a measurement of the 60Fe neutron capture cross section at the energy of kT = 90 keV is planned at Goethe University Frankfurt, Germany.
Having the neutron capture cross section of 60Fe at the energy of kT = 25 keV measured in the year 2009 in Karlsruhe , at the energy of kT = 25 meV measured in May 2012 at Johannes Gutenberg University in Mainz and at the planned energy of kT = 90 keV at Goethe University Frankfurt, there will be three points for
the extrapolation of the values for the neutron capture cross section of 60Fe. This will lead to a significant reduction in uncertainty with respect to existing theoretical discrepancies.
Linguistic tug-of-war : French and German in Alsace, 1945
- This thesis investigates the linguistic effects of language contact between French and German in Alsace due to the German annexation of this region during World War II. The turbulent, tug-of-war history of Alsace has constantly challenged the Alsatian people to secure a stable cultural and national identity. This study focuses on understanding the development of the linguistic aspect of this Alsatian identity. My hypothesis is that there was a greater French influence on Alsatian speech after World War II due to the anti-German sentiment provoked by the harsh Nazi policies during the war. To test this hypothesis, this study analyzes and compares the type and regularity of lexical borrowings from French into German and from German into French in Alsatian newspapers in 1945.