Filtern
Erscheinungsjahr
- 2014 (130) (entfernen)
Dokumenttyp
Volltext vorhanden
- ja (130)
Gehört zur Bibliographie
- nein (130)
Schlagworte
- Beschleuniger (2)
- Beschleunigerphysik (2)
- Dyson–Schwinger equations (2)
- Ionenstrahl (2)
- Nonperturbative methods (2)
- Nucleus–nucleus collisions (2)
- Nukleosynthese (2)
- Particle Accelerator (2)
- Radio Frequenz Quadrupol (2)
- Strahldynamik (2)
Institut
- Physik (130) (entfernen)
The traffic AAA-ATPase PilF is essential for pilus biogenesis and natural transformation of Thermus thermophilus HB27. Recently, we showed that PilF forms hexameric complexes containing six zinc atoms coordinated by conserved tetracysteine motifs. Here we report that zinc binding is essential for complex stability. However, zinc binding is neither required for pilus biogenesis nor natural transformation. A number of the mutants did not exhibit any pili during growth at 64 °C but still were transformable. This leads to the conclusion that type 4 pili and the DNA translocator are distinct systems. At lower growth temperatures (55 °C) the zinc-depleted multiple cysteine mutants were hyperpiliated but defective in pilus-mediated twitching motility. This provides evidence that zinc binding is essential for the role of PilF in pilus dynamics. Moreover, we found that zinc binding is essential for complex stability but dispensable for ATPase activity. In contrast to many polymerization ATPases from mesophilic bacteria, ATP binding is not required for PilF complex formation; however, it significantly increases complex stability. These data suggest that zinc and ATP binding increase complex stability that is important for functionality of PilF under extreme environmental conditions.
Weltweit arbeiten Astrophysiker noch immer mit einer Theorie, die bereits vor rund 100 Jahren aufgestellt wurde – die Einstein’sche Relativitätstheorie. Nahezu jeder hat den genialen Kopf dahinter vor Augen: Albert Einstein. Was aber ist der von Einstein prognostizierte gekrümmte Raum, was sind schwarze Löcher und Neutronensterne und wer sind die Menschen, die auf diesen Gebieten forschen? Luciano Rezzolla, seit Oktober 2013 Professor für Theoretische Astrophysik an der Goethe-Universität sowie Leiter einer Arbeitsgruppe am Max-Planck-Institut für Gravitationsphysik in Potsdam, ist einer dieser Forscher.
Nichtinvasive Detektoren für ortsaufgelöste Strahlprofilmessungen gewinnen mit zunehmenden Strahlströmen und -energien immer mehr an Bedeutung. An der Universität Frankfurt im Institut für Angewandte Physik (IAP) wird ein “Figure Eight”-förmiger magnetostatischer Speichering mit Stellarator-Konfiguration (F8SR) entwickelt. Einige Aspekte der Strahldynamik in einem solchen Ring können mit einem experimentellen Aufbau am IAP untersucht werden. Die Herausforderung bei der Entwicklung eines Detektors an einem (F8SR) liegt auf der einen Seite darin den Strahl nichtinvasiv zu detektieren, und andererseits müssen magnetisch unempfindliche Komponenten für den Detektor ausgewählt werden. Dabei sollte der Detektor so flexibel sein, dass der Strahl entlang der Flugbahn transversal gemessen werden kann. In dieser Arbeit geht es um einen Detektor mit radial um den Strahl angeordneten Photodioden, mit deren Hilfe die strahlinduzierte Fluoreszenz detektiert wird und mit einem geeigneten Rekonstruktionsverfahren, Strahlposition und den Strahldurchmesser ermittelt werden kann. Die Messungen werden mit einem weiteren schon erprobten Detektor - einem Szintillationsschirm verglichen.
The colour-singlet axial-vector vertex plays a pivotal role in understanding dynamical chiral symmetry breaking and numerous hadronic weak interactions, yet scant model-independent information is available. We therefore use longitudinal and transverse Ward–Green–Takahashi (WGT) identities, together with kinematic constraints, in order to ameliorate this situation and expose novel features of the axial vertex: amongst them, Ward-like identities for elements in the transverse piece of the vertex, which complement and shed new light on identities determined previously for components in its longitudinal part. Such algebraic results are verified via solutions of the Bethe–Salpeter equation for the axial vertex obtained using two materially different kernels for the relevant Dyson–Schwinger equations. The solutions also provide insights that suggest a practical Ansatz for the axial-vector vertex.
In dieser Arbeit wurde der langsame Neutroneneinfang (s-Prozess) mit dem Nukleosynthese-Programm NETZ simuliert. Ziel solcher Programme ist es, die solare Häufigkeitsverteilung zu reproduzieren.
Der s-Prozess dient der Synthese von Elementen schwerer als Eisen und ereignet sich in astrophysikalischen Szenarien mit relativ geringen Neutronendichten. Dadurch sind die Neutroneneinfangzeiten meist größer als die Betazerfallszeiten und der Prozesspfad folgt dem Stabilitätstal in der Nuklidkarte. Aus diesem Grund sind die Reaktionsraten gut messbar und es steht ein umfangreiches Daten-Netzwerk zur Verfügung, welches in die Simulationen einfließen kann.
Man unterschiedet zwischen der schwachen- und der Hauptkomponente des s-Prozesses. Die schwache Komponente findet in massereichen Sternen (M > 8M⊙) beim Helium-Kernbrennen und Kohlenstoff-Schalenbrennen statt. Bei Temperaturen über 2.5 × 108 K wird die Reaktion 22Ne(α ,n)25Mg aktiviert, welche Neutronen liefert, die von der Eisensaat eingefangen werden. Bei einer mittleren Neutronendichte von 106/cm3 reicht die Neutronenbestrahlung jedoch nicht aus, um den Synthesefluss über die abgeschlossene Neutronenschale bei N = 50 hinweg zu treiben. Folglich werden nur Isotope zwischen Eisen und Yttrium (56 < A < 90) aufgebaut.
Schwerere Isotope (90 ≤ A ≤ 208) werden dagegen in der Hauptkomponente synthetisiert. Diese findet in thermisch pulsierenden AGB-Sternen statt, in denen während des Helium-Schalenbrennens Neutronen hauptsächlich über die Reaktion 13C(α ,n)16O zur Verfügung gestellt werden.
Am Ende der jeweiligen Brennphasen gibt es einen Anstieg von Temperatur und Neutronendichte, welche jedoch nicht die globale Häufigkeitsverteilung, wohl aber Verzweigungspunkte beeinflussen können. An diesen Punkten liegen die Neutroneneinfang- und Betazerfallszeiten in der gleichen Größenordnung, sodass der s-Prozesspfad aufspaltet.
Hinzu kommt, dass unter stellaren Bedingungen die Reaktionsraten starken Änderungen unterworfen sein können. Bei hohen Temperaturen und Dichten befinden sich die Kerne in angeregten Zuständen, die wie auch der Grundzustand Neutronen einfangen oder radioaktiv zerfallen können, jedoch bei veränderten Raten. Dieser Sachverhalt kann einen Einfluss auf die Häufigkeitsverteilung haben.
Das umfangreiche Reaktionsnetzwerk des s-Prozesses kann schnell und mit guter Genauigkeit mit dem Programm NETZ berechnet werden. Dabei muss dem Programm ein Neutronenpuls - der zeitliche Verlauf von Neutronendichte und Temperatur - vorgegeben werden. Ziel dieser Arbeit war es, einen geeigneten solchen Puls zu finden, um die bisherigen Ergebnisse von NETZ zu optimieren. Außerdem wurde eine Aktualisierung der Reaktionsraten und solaren Häufigkeitsverteilung durchgeführt.
Die neuen Neutronenpulse für die schwache- und Hauptkomponente liefern eine Verbesserung in der Übereinstimmung von berechneter und solarer Häufigkeit. Dabei konnte für die Hauptkomponente sowohl ein Profil mit einem rechteckigen als auch mit einem exponentiellen Verlauf der Neutronendichte gefunden werden.
Darüber hinaus bietet NETZ die Möglichkeit, den Einfluss veränderter Reaktionsraten auf die Häufigkeitsverteilung abzuschätzen. Dazu steht inzwischen auch ein Online-Interface zur Verfügung. Dies ist besonders interessant, wenn es neue Messungen z.B. für Neutroneneinfangreaktionen gibt und man die Relevanz für den s-Prozess bestimmen möchte. So konnte in dieser Arbeit die Bedeutung der kürzlich neu gemessenen Raten für 63,65Cu(n,γ) und 69,71Ga(n,γ) beurteilt werden.
Ultrafast protein dynamics are of great interest for understanding the molecular basis of biochemical function. One method to study structural changes with highest time-resolution starting in the femtosecond regime is 2D-IR spectroscopy. However its application to investigate protein dynamics both with high temporal and spatial resolution is currently limited to few biological systems with intrinsic chromophores. Spectral congestion, the contribution of many similar oscillators to the same signals, makes it difficult to draw conclusions about local structural dynamics in most other proteins.
The aim of this thesis is to extend the application of 2D-IR spectroscopy to a wider range of proteins by introducing unnatural amino acids (UAAs) with azide or nitrile groups as site-specific vibrational probes, which absorb in the free spectral window between 1800 to 3000 cm-1 by using methods from chemical biology.
In a comparative experimental study using FTIR and 2D-IR spectroscopy of single amino acids azidohomoalanine (Aha), a methionine analogue, was identified as preferred label. To demonstrate the application potential of UAAs as site-specific probes, Aha was then incorporated into different positions in a small globular protein. By using both FTIR and ultrafast 2D-IR it was shown, that indeed the local microenvironment as well as conformational fluctuations on picosecond timescale could be monitored with high spatial information. The azide moiety shows a shift of its absorption frequency depending on the polarity of its surrounding. Using this approach, different subensembles for the protein conformations with more polar and less polar environment around the vibrational probe can be distinguished.
A second major application of site-specific labels is the study of vibrational energy transfer processes (VET), predicted to be relevant for allosteric communication in protein domains such as the PDZ domain. VET can be tracked with high spatial resolution using time-resolved IR spectroscopy by exciting a localized vibrational mode and probing separate modes in a two-colour 2D-IR experiment. To extend this kind of experiment to proteins, a specific donor-acceptor pair of two UAAs was introduced. It uses an azulene moiety as donor that can be excited in the visible range but deposits the excess energy by internal conversion into the vibrational modes of the ground state. In small peptides this VET pair was applied successfully, showing a distance-dependent energy transfer induced signal for VET through covalent bonds. These findings bare great promise for the direct observation of vibrational energy flow in proteins in real-time.
Overall this thesis is the basis for extending the usability of 2D-IR spectroscopy to study structural dynamics in a wide range of proteins systems both with high temporal and spatial resolution.
In this thesis, Planck size black holes are discussed. Specifically, new families of black holes are presented. Such black holes exhibit an improved short scale behaviour and can be used to implement gravity self-complete paradigm. Such geometries are also studied within the ADD large extra dimensional scenario. This allows black hole remnant masses to reach the TeV scale. It is shown that the evaporation endpoint for this class of black holes is a cold stable remnant. One family of black holes considered in this thesis features a regular de Sitter core that counters gravitational collapse with a quantum outward pressure. The other family of black holes turns out to nicely fit into the holographic information bound on black holes, and lead to black hole area quantization and applications in the gravitational entropic force. As a result, gravity can be derived as emergent phenomenon from thermodynamics.
The thesis contains an overview about recent quantum gravity black hole approaches and concludes with the derivation of nonlocal operators that modify the Einstein equations to ultraviolet complete field equations.
Tuning and optimization of the field distribution for 4-rod radio frequency quadrupole linacs
(2014)
In this thesis, the tuning process of the 4-rod Radio Frequency Quadrupole has been analyzed and a theory for the prediction of the tuning plate's influence on the longitudinal voltage distribution was developed together with RF design options for the optimization of the fringe fields.
The basic principles of the RFQ's particle dynamics and resonant behavior are introduced in the theory part of this thesis. All studies that are presented are based on the work on four RFQs of recent linac projects. These RFQs are described in one chapter. Here, the projects are introduced together with details about the RFQ parameters and performance. In the meantime two of these RFQs are in full operation at NSCL at MSU and FNAL. One is operating in the test phase of the MedAustron Cancer Therapy Center and the fourth one for LANL is about to be built. The longitudinal voltage distribution has been studied in detail with a focus on the influence of the RF design with tuning elements and parameters like the electrodes overlap or the distance between stems. The theory for simulation methods for the field flatness that were developed as part of this thesis, as well as its simulation with CST MWS have been analyzed and compared to measurements. The lumped circuit model has proven to predict results with an accuracy that can be used in the tuning process of 4-rod RFQs. Together with results from the tuning studies, the studies on the fringe fields of the 4-rod structure lead to a proposal for a 4-rod RFQ model with an improved field distribution in the transverse and longitudinal electric field.
The present work deals with the integration of variable renewable energy sources, wind and solar energy into the European and US power grid. In contrast to other networks, such as the gas supply mains, the electricity network is practically not able to store energy. Generation and consumption therefore always have tobe balanced. Currently, the load curve is viewed as a rigid boundary condition, which must be followed by the generation system. The basic idea of the approach followed here is that weather-dependent generation causes a shift of focus of the electricity supply. At high shares of wind and solar generation, the role of the rigid boundary condition falls to the residual load, that is, the remaining load after subtraction of renewable generation. The goal is to include the weather dependence as well as the load curve in the design of the future electricity supply.
After a brief introduction, the present work first turns to the underlying weather-, generation and load data, which form the starting point of the analysis. In addition, some basic concepts of energy economics are discussed, which are needed in the following.
In the main part of the thesis, several algorithms are developed to determine the load flow in a network with a high share of wind and solar energy and to determine the backup supply needed at the same time. Minimization of the energy needed from controllable power plants, the capacity variable power plants, and the capacity of storing serve as guiding principles. In addition, the optimization problem of grid extensions is considered. It is shown that it can be formulated as a convex optimization problem. It turns out that with an optimized, international transmission network which is about four times the currently available transmission capacity, much of the potential savings in backup energy (about 40%) in Europe can be reached. In contrast, a twelvefold increase the transmission capacity would be necessary for a complete implementation of all possible savings in dispatchable power plants.
The reduction of the dispatchable generation capacity and storage capacity, however, presents a greater challenge. Due to correlations in the generation of time series of individual countries, it may be reduced only with difficulty, and by only about 30%.
In the following, the influence of the relative share of wind and solar energy is illuminated and examined the interplay with the line capacitance. A stronger transmission network tends to lead to a higher proportion of wind energy being better integrated. With increasing line capacity, the optimal mix in Europe therefore shifts from about 70% to 80% wind. Similar analyses are carried out for the US with comparable results.
In addition, the cost of the overall system can be reduced. It is interesting at this point that the advantages for the network integration may outweigh higher production costs of individual technologies, so that it is more favourable from the viewpoint of the entire system to use the more expensive technologies.
Finally, attention is given to the flexibility of the dispatchable power plants. Starting from a Fourier-like decomposition of the load curve as it was a few years ago, when hardly renewable generation capacity was present, capacities of different flexibility classes of dispatchable power plant are calculated. For this purpose, it is assumed that the power plant park is able to follow the load curve without significant surplusses or deficits. From this examination, it is derived what capacity must at least be available without having to resort to a detailed database of existing power plants.
Assuming a strong European cooperation, with a stronger international transmission network, the dispatchable power capacity can be significantly reduced while maintaining security of supply and generating relatively small surplusses in dispatchable power plants.
Top-down influences on ambiguous perception: the role of stable and transient states of the observer
(2014)
The world as it appears to the viewer is the result of a complex process of inference performed by the brain. The validity of this apparently counter-intuitive assertion becomes evident whenever we face noisy, feeble or ambiguous visual stimulation: in these conditions, the state of the observer may play a decisive role in determining what is currently perceived. On this background, ambiguous perception and its amenability to top-down influences can be employed as an empirical paradigm to explore the principles of perception. Here we offer an overview of both classical and recent contributions on how stable and transient states of the observer can impact ambiguous perception. As to the influence of the stable states of the observer, we show that what is currently perceived can be influenced (1) by cognitive and affective aspects, such as meaning, prior knowledge, motivation, and emotional content and (2) by individual differences, such as gender, handedness, genetic inheritance, clinical conditions, and personality traits and by (3) learning and conditioning. As to the impact of transient states of the observer, we outline the effects of (4) attention and (5) voluntary control, which have attracted much empirical work along the history of ambiguous perception. In the huge literature on the topic we trace a difference between the observer's ability to control dominance (i.e., the maintenance of a specific percept in visual awareness) and reversal rate (i.e., the switching between two alternative percepts). Other transient states of the observer that have more recently drawn researchers' attention regard (6) the effects of imagery and visual working memory. (7) Furthermore, we describe the transient effects of prior history of perceptual dominance. (8) Finally, we address the currently available computational models of ambiguous perception and how they can take into account the crucial share played by the state of the observer in perceiving ambiguous displays.
This thesis serves two main purposes:
1. The introduction of a novel experimental method to investigate phase change dynamics of supercooled liquids
2. First-time measurements for the crystallization behaviour for hydrogen isotopes under various conditions
1) The new method is established by the synergy of a liquid microjet of ~ 5 µm diameter and a scattering technique with high spatial resolution, here linear Raman spectroscopy. Due to the high directional stability and the known velocity of the liquid filament, its traveling axis corresponds to a time axis static in space. Utilizing evaporative cooling in a vacuum environment, the propagating liquid cools down rapidly and eventually experiences a phase transition to the crystalline state. This temporal evolution is probed along the filament axis, ultimately resulting in a time resolution of 10 ns. The feasibility of this approach is proven successfully within the following experiments.
2) A main object of study are para-hydrogen liquid filaments. Raman spectra reveal a temperature gradient of the liquid across the filament. This behaviour can quantitatively be reconstructed by numerical simulations using a layered model and is rooted in the effectiveness of evaporative cooling on the surface and a finite thermal conductivity. The deepest supercoolings achieved are ~ 30% below the melting point, at which the filament starts to solidify from the surface towards the core. With a crystal growth velocity extracted from the data the appropriate growth mechanism is identified. The crystal structure that initially forms is metastable and probably the result of Ostwald’s rule of stages. Indications for a transition within the solid towards the stable equilibrium phase support this interpretation.
The analog isotope ortho-deuterium is evidenced to behave qualitatively similar with quantitative differences being mass related.
In further measurements, isotopic mixtures of para-hydrogen and ortho-deuterium are investigated. It is found that the crystallization process starts earlier and lasts significantly longer compared to the pure substances with the maximum values between 20-50% ortho-deuterium content. A solely temperature based explanation for this effect can be excluded. The difference in the quantum character and hence effective size of the isotopes suggests a strong influence of the progressing liquid-solid-interface. Small dilutions of each para-hydrogen and ortho-deuterium with neon show an even more extended crystallization process compared to above isotopic mixtures. Additionally, the crystal is strongly altered in favor of the equilibrium lattice structure of neon.
We study the phase structure of QCD at finite temperature within a Polyakov-loop extended quark–meson model. Such a model describes the chiral as well as the confinement-deconfinement dynamics. In the present investigation, based on the approach and results put forward in [1], [2], [3], [4], both matter and glue fluctuations are included. We present results for the order parameters as well as some thermodynamic observables and find very good agreement with recent results from lattice QCD.
In this thesis, different physical and electrical aspects of silicon microstrip sensors and low-mass multi-line readout cables have been investigated. These silicon microstrip sensors and readout cables will be used in the Silicon Tracking System (STS) of the fixed-target heavy-ion Compressed Baryonic Matter (CBM) experiment which is under development at the upcoming Facility for Antiproton and ion Research (FAIR) in Darmstadt, Germany. The highly segmented low-mass tracking system is a central CBM detector system to resolve the high tracking densities of charged particles originating from beam-target interactions. Considering the low material budget requirement the double-sided silicon microstrip detectors have been used in several planar tracking stations. The readout electronics is planned to be installed at the periphery of the tracking stations along with the cooling system. Low-mass multi-line readout cables shall bridge the distance between the microstrip sensors and the readout electronics. The CBM running operational scenario suggests that some parts of the tracking stations are expected to be exposed to a total integrated particle fluence of the order of 1e14 neq/cm2. After 1e14 neq/cm2 the damaged modules in the tracking stations will be replaced. Thus radiation hard sensor is an important requirement for the sensors. Moreover, to cope with the high reaction rates, free-streaming (triggerless) readout electronics with online event reconstruction must be used which require high signal-to-noise (SNR) ratio (i.e., high signal efficiency, low noise contributions). Therefore, reduction in noise is a major goal of the sensor and cable development.
For better insight into the different aspects of the silicon microstrip sensors and multi-line readout cables, the simulation study has been performed using SYNOPSYS TCAD tools. 3D models of the silicon microstrip sensors and the readout cables were implemented which is motivated by the stereoscopic construction of the silicon microstrip sensors. For the evaluation of the performance of the silicon microstrip sensors in the harsh radiation environment during experimental operation, a radiation damage model has been included. It reproduces the behavior of the irradiated CBM prototype sensors. In addition to the static characteristics, the interstrip parameters relevant to understand strip isolation and cross-talk issues have been extracted. The transient simulations have been performed to estimate the charge collection performance of the irradiated sensors. The signal transmission in the readout cables has been evaluated with the finite element simulation tool RAPHAEL. Based on the performance of the front-end electronics used for early prototyping in the CBM experiment, capacitive and resistive noise contributions from the silicon microstrip sensors and multi-line readout cables have been extracted.
To validate the aforementioned simulations, numerous tests have been performed both on the multi-line readout cables and silicon microstrip sensors. Characterizations of multi-line readout cables and silicon microstrip sensors in laboratory conditions have been found to agree reasonably well with the simulations. Considering the expected radiation environment the behavior of silicon microstrip sensors have been studied especially in terms of noise and charge collection efficiency. Source-scan of the silicon microstrip sensors using 241Am is presented. In order to test a first system of detector stations including the data acquisition system, slow control and online monitoring software and for track reconstruction, in-beam tests have been performed at the COSY synchrotron of the Research Center Juelich, Germany. Further, different design parameters have been suggested to improve the sensor and readout cable design on the basis of the simulations and the measurements. Many of these parameters have been implemented in the new prototypes under production. These new prototypes will be tested in-beam by the end of 2013.
The quark gluon plasma produced in heavy ion collisions behaves like an almost ideal fluid described by viscous hydrodynamics with a number of transport coefficients. The second order coefficient κ is related to a Euclidean correlator of the energy-momentum tensor at vanishing frequency and low momentum. This allows for a lattice determination without maximum entropy methods or modelling, but the required lattice sizes represent a formidable challenge. We calculate κ in leading order lattice perturbation theory and simulations on 1203 × 6, 8 lattices with a < 0.1 fm. In the temperature range 2Tc − 10Tc we find κ = 0.36(15)T2. The error covers both a suitably rescaled AdS/CFT prediction as well as, remarkably, the result of leading order perturbation theory. This suggests that appropriate noise reduction methods on the lattice and NLO perturbative calculations could provide an accurate QCD prediction in the near future.
The phase diagram of the square lattice bilayer Hubbard model: a variational Monte Carlo study
(2014)
We investigate the phase diagram of the square lattice bilayer Hubbard model at half-filling with the variational Monte Carlo method for both the magnetic and the paramagnetic case as a function of the interlayer hopping and on-site Coulomb repulsion U. With this study we resolve some discrepancies in previous calculations based on the dynamical mean-field theory, and we are able to determine the nature of the phase transitions between metal, Mott insulator and band insulator. In the magnetic case we find only two phases: an antiferromagnetic Mott insulator at small for any value of U and a band insulator at large . At large U values we approach the Heisenberg limit. The paramagnetic phase diagram shows at small a metal to Mott insulator transition at moderate U values and a Mott to band insulator transition at larger U values. We also observe a re-entrant Mott insulator to metal transition and metal to band insulator transition for increasing in the range of . Finally, we discuss the phase diagrams obtained in relation to findings from previous studies based on different many-body approaches.
We have measured the radiative neutron-capture cross section and the total neutron-induced cross section of one of the most important isotopes for the s process, the 25Mg. The measurements have been carried out at the neutron time-of-flight facilities n_TOF at CERN (Switzerland) and GELINA installed at the EC-JRC-IRMM (Belgium). The cross sections as a function of neutron energy have been measured up to approximately 300 keV, covering the energy region of interest to the s process. The data analysis is ongoing and preliminary results show the potential relevance for the s process.
The nature of spontaneous brain activity during wakefulness and sleep: a complex systems approach
(2014)
In this thesis we study the organization of spontaneous brain activity during wakefulness and all stages of human non-rapid eye movement sleep using an approach based on developments and tools from the theory of complex systems. After a brief introduction to sleep physiology and different theoretical models of consciousness, we study how the organization of cortical and sub-cortical interactions is modified during the sleep cycle. Our results, obtained by modeling global brain activity as a complex functional interaction network, show that the capacity of the human brain to integrate different segregated functional modules is diminished during deep sleep, in line with an informationintegration account of consciousness. We then show that integration is impaired not only across space but also in the temporal domain, by assesing the emergence of long-range temporal correlations in brain activity and how they are modified during sleep. We propose an encompassing explanation for this observation, namely, that the brain operatsat different dynamical regimes during different states of consciousness. Finally, we gather massive amounts of data from different collaborative projects and apply machine learning techniques to reveal that the \resting state" cannot be considered as a pure brain state and is in fact a mixture containing different levels of conscious awareness. This last result has deep implications for future attempts to develop a discovery science of brain function both in health and disease.
Within the nucleosynthetic processes of the slow neutron-capture reaction network (called the s process) the so called branching points, unstable isotopes where different nuclear reactions are competing, are important to understand . For modeling and calculating the nucleosynthesis and compare the resulting abundances to the observed ones, it is indispensable to know the branching ratios as well as the corresponding cross sections.
A great challenge in measuring those rates in experiments may be the radioactivity of the isotopes involved, which can make it nearly impossible to manufacture the needed targets. In addition, in stellar environments the excited states of isotopes can be in equilibrium with the ground state, affecting the half-lives and the branching ratios significantly. The isotope 152Eu is such a branching point, with neutron captures and β-decays competing. Those challenges were approached in the s405 experiment performed at the GSI Helmholtzzentrum für Schwerionenforschung GmbH: the challenge the challenge of the radioactivity can be approached by experiments carried out in inverse kinematics with radioactive beams, solving the problem of unstable targets. Also a reversed reaction was used to access the excited states of the studied isotope. The performed 152Sm(p,n)152Eu is a pioneering attempt to use those methods on heavy ions. The (p,n) reaction was used as a substitute for electron capture, the focus lies on reactions with low-momentum transfers, resulting in the emission of low-energy neutrons. The new developed low-energy detector array LENA was put to test for the fist time in the s405 experiment.
We report on the measurement of the inclusive Υ (1S) production in Pb–Pb collisions at √sNN = 2.76 TeV carried out at forward rapidity (2.5 < y < 4) and down to zero transverse momentum using its μ+μ−decay channel with the ALICE detector at the Large Hadron Collider. A strong suppression of the inclusive Υ (1S) yield is observed with respect to pp collisions scaled by the number of independent nucleon–nucleon collisions. The nuclear modification factor, for events in the 0–90% centrality range, amounts to 0.30 ± 0.05(stat) ± 0.04(syst). The observed Υ (1S) suppression tends to increase with the centrality of the collision and seems more pronounced than in corresponding mid-rapidity measurements. Our results are compared with model calculations, which are found to underestimate the measured suppression and fail to reproduce its rapidity dependence.
Fission fragment mass distributions were measured in heavy-ion induced fissions using 238U target nucleus. The measured mass distributions changed drastically with incident energy. The results are explained by a change of the ratio between fusion and qasifission with nuclear orientation. A calculation based on a fluctuation dissipation model reproduced the mass distributions and their incident energy dependence. Fusion probability was determined in the analysis, and the values were consistent with those determined from the evaporation residue cross sections.
In dieser Arbeit wurde die Leistungsfähigkeit des neuen Inner Tracking System (ITS) in Bezug auf die Messung von Spektren der invarianten Masse von Dielektronpaaren im Rahmen des ALICE Experiments am LHC ausgewertet. Zu Beginn der Planungen zum zukünftigen ITS wurden zwei verschiedene Designmöglichkeiten in Betracht gezogen: Auf der einen Seite ein ITS, welches die Möglichkeit zur Teilchenidentifizierung mittels spezifischem Energieverlust pro Wegstrecke bietet und auf der anderen Seite ein ITS welches diese Möglichkeiten nicht hat. Es wurde untersucht, ob es zukünftig möglich sein wird aus der Steigung des Spektrums der invarianten Masse von Dileptonen zwischen 1,1 GeV/c2 < Mee < 2,0 GeV/c2 direkt die Temperatur des Quark-Gluon-Plasmas zu extrahieren. Weiterhin wurde geprüft welches der beiden Systeme diese Aufgabe besser erfüllt.
Das neue ITS bietet gegenüber dem alten ITS Vorteile, die in dieser Analyse genutzt wurden. Zuerst, siehe Abschnitt 3.4, wurde ein zweidimensionaler Schnitt auf den Öffnungswinkel und die invariante Masse angewandt um Elektronen und Positronen aus Dalitzzerfällen und Photonkonversionen zu identifizieren und für die folgende Analyse zu verwerfen. Hierzu wurde die verbesserte Spurfindungseffizienz hin zu kleinen Transversalimpulsen ausgenutzt, um die Anzahl an zu kombinierenden Teilchen und damit die Wahrscheinlichkeit richtige Paare zu finden, zu erhöhen. Allerdings können Teilchen, welche nur im ITS nachgewiesen werden können, nicht zweifelsfrei (ITSPID), beziehungsweise gar nicht (ITSnoPID) identifiziert werden. Die Simulationen ergeben, dass ein zukünftiges ITS mit der Möglichkeit zur Teilchenidentifizierung leicht bessere Werte in der Signifikanz und im Verhältnis von Signal zu Untergrund liefern kann.
Die verbesserte Vertexfindung wird zur Reduktion des Beitrags durch Elektronen und Positronen aus semileptonisch zerfallenden D-Mesonen (Abschnitt 3.4.4) ausgenutzt.
Die Elektronen und Positronen, welche nach den Schnitten in der Stichprobe blieben, wurden verwendet um den Untergrund zu simulieren (Abschnitt 3.4.5). Daraufhin wurde die Signifikanz und das Verhältnis von Signal zu Untergrund berechnet. Mit diesen Informationen (Abschnitt 3.5.3) wurde ein Spektrum der invarianten Masse von Dileptonen mit der zu erwartenden Anzahl von 2,5 · 109 zentralen Blei-Blei-Kollisionen erzeugt. Dies führt zu den in Abschnitt 3.5.4 gezeigten Spektren. Nach Abzug der Beiträge durch die semileptonischen D-Meson Zerfälle und durch den hadronischen Cocktail ist noch der zu erwartende Beitrag durch die thermische Strahlung (Abschnitt 1.5) im Spektrum vorhanden. Eine Parametrisierung dieser Kurve ergibt die Temperatur des Quark-Gluon-Plasmas.
Der Unterschied der ermittelten Messwerte der Temperatur zwischen dem zukünftigen ITS mit Teilchenidentifizierung und ohne ist gering (Abschnitt 3.5.5). Die Messung ergibt keine signifikanten Unterschiede zwischen beiden ITS Entwürfen. Aufgrund dieses Ergebnisses kann man sagen, dass für die Messung von Dileptonen im Niedrigmassenbereich keine ITS PID notwendig ist. In den mittlerweile veröffentlichten ITS Technical Design Report sind die Ergebnisse dieser Studie eingeflossen. Es wurde beschlossen, dass der ITSnoPID umgesetzt wird.
We study the equilibrium properties of strongly-interacting infinite parton-hadron matter, characterized by the transport coefficients such as shear and bulk viscosity and electric conductivity, and the non-equilibrium dynamics of heavy-ion collisions within the Parton-Hadron-String Dynamics (PHSD) transport approach, which incorporates explicit partonic degrees of freedom in terms of strongly interacting quasiparticles (quarks and gluons) in line with an equation of state from lattice QCD as well as the dynamical hadronization and hadronic collision dynamics in the final reaction phase. We discuss in particular the possible origin for the strong elliptic flow v2 of direct photons observed at RHIC energies.
Within the statistical model, the net strangeness conservation and incomplete total strangeness equilibration lead to the suppression of strange particle multiplicities. Furthermore, suppression effects appear to be stronger in small systems. By treating the production of strangeness within the canonical ensemble formulation we developed a simple model which allows to predict the excitation function of K+/π+ ratio in nucleus–nucleus collisions. In doing so we assumed that different values of K+/π+, measured in p + p and Pb + Pb interactions at the same collision energy per nucleon, are driven by the finite size effects only. These predictions may serve as a baseline for experimental results from NA61/SHINE at the CERN SPS and the future CBM experiment at FAIR.
In der vorliegenden Arbeit werden Stabilitätstests an einer Vieldrahtproportionalkammer nach ALICE-Geometrie vorgestellt. Wegen elektrischer Instabilitäten, das heißt dem Abschalten der Hochspannungsversorgung einzelner Kammern aufgrund von Entladungen an der Ausleseebene, wurde die ALICE-TPC bisher mit zwei unterschiedlichen Gasmischungen betrieben. Es wurden die Gasmischungen Ne-CO2 (90-10) und Ne-CO2-N2 (90-10-5) verwendet.
In dieser Arbeit soll nun mit systematischen Stabilitätstests mit einer α- und einer γ-Quelle am Testaufbau am IKF untersucht werden, ob eine Beimischung von Stickstoff zur Gasmischung Ne-CO2 wirklich positive Auswirkungen auf die elektrische Stabilität der Vieldrahtproportionalkammern der ALICE-TPC hat. Messungen mit der Gasmischung Ar-CO2 (90-10) dienen dabei als Referenzmessungen.
Zunächst wurden vorbereitende Messungen zum bessseren Verständnis des Einflusses der Ausleseelektronik auf die Padsignale am Testaufbau durchgeführt. Die Untersuchung der von einem Pulser induzierten Signale zeigt, dass keine Korrektur der Nullverschiebung nötig ist. Auÿerdem konnten durch diese Messung die Verstärkungsfaktoren des verwendeten Hauptverstärkers ermittelt werden. Ein weiterer wichtiger Faktor für Stabilitätstests ist die Genauigkeit des Mischungsverhältnisses des Gases. Um eine hohe Genauigkeit zu gewährleisten, wurde der Gasfliss der verschiedenen Kanäle des zur Herstellung der Gasmischung genutzten Gasmischers überprüft und so die Bereiche für den Gasfluss gefunden, in denen sich das Mischungsverhältnis nicht ändert.
Eine gute Auflösung kann mit Vieldrahtproportionalkammern erreicht werden, wenn die Kammern auch bei einem möglichst groÿen Gain noch stabil betrieben werden können. Um den Gain aus Anodestrommessungen bestimmen zu können, wurden die Primärströme für die α- und die γ-Quelle ermittelt.
Frühere Messungen mit einer γ-Quelle, aufgrund derer Stickstoff als Beimischung in den Fokus rückte, ließen vermuten, dass sich durch die Beimischung von Stickstoff die Stabilität der Auslesekammern verbessern lassen würde. Die durchgeführten Messungen mit der γ-Quellen sollten diese Aussage nun überprüfen. Sie können die früheren Ergebnisse jedoch nicht bestätigen, sondern zeigen, dass die Gasmischung Ne-CO2-N2 (90-10-5) im Gegensatz zur Gasmischung Ne-CO2 (90-10) bei Bestrahlung mit der γ-Quelle zu instabileren Bedingungen für die Auslesekammer führt.
Zum Erzeugen der Anodensignale bei Stabilitätstests wurden erstmals geladene Teilchen aus einer α-Quelle verwendet. Im Gegensatz zur Messung mit der γ-Quelle kann die Auslesekammer bei der Beimischung von Stickstoff zu Ne-CO2 bis zu einem um 25% höheren Gain stabil betrieben werden als bei der Gasmischung Ne-CO2.
Aufgrund des je nach verwendeter Quelle unterschiedlichen Effekts auf die Stabilität der Auslesekammer lässt sich nicht mit absoluter Sicherheit sagen, ob eine Beimischung von Stickstoff die gewünschten Auswirkungen hat. Allerdings werden die Spuren in der ALICE-TPC durch geladene Teilchen hervorgerufen, sodass die Messungen mit der α-Quelle den experimentellen Bedingungen bei ALICE näher kommen als die Messungen mit der γ-Quelle und deshalb die Gasmischung Ne-CO2-N2 (90-10-5) zu bevorzugen ist.
In self-organized critical (SOC) systems avalanche size distributions follow power-laws. Power-laws have also been observed for neural activity, and so it has been proposed that SOC underlies brain organization as well. Surprisingly, for spiking activity in vivo, evidence for SOC is still lacking. Therefore, we analyzed highly parallel spike recordings from awake rats and monkeys, anesthetized cats, and also local field potentials from humans. We compared these to spiking activity from two established critical models: the Bak-Tang-Wiesenfeld model, and a stochastic branching model. We found fundamental differences between the neural and the model activity. These differences could be overcome for both models through a combination of three modifications: (1) subsampling, (2) increasing the input to the model (this way eliminating the separation of time scales, which is fundamental to SOC and its avalanche definition), and (3) making the model slightly sub-critical. The match between the neural activity and the modified models held not only for the classical avalanche size distributions and estimated branching parameters, but also for two novel measures (mean avalanche size, and frequency of single spikes), and for the dependence of all these measures on the temporal bin size. Our results suggest that neural activity in vivo shows a mélange of avalanches, and not temporally separated ones, and that their global activity propagation can be approximated by the principle that one spike on average triggers a little less than one spike in the next step. This implies that neural activity does not reflect a SOC state but a slightly sub-critical regime without a separation of time scales. Potential advantages of this regime may be faster information processing, and a safety margin from super-criticality, which has been linked to epilepsy.
Single-pion production in proton-proton collisions at 1.25 GeV: measurements by HADES and a PWA
(2014)
We report on the single-pion production in proton-proton collisions at a kinetic energy of 1.25 GeV based on data measured with HADES. Exclusive channels npπ+ and ppπ0 were studied simultaneously. The parametrization of production cross sections of the one-pion final states by means of the resonance model has been obtained. Independently, the extraction of the leading partial waves in the data were analyzed within the framework of the partial wave analysis (PWA). Contributions for the production of ∆(1232) and N(1440) intermediate states have been deduced.
Im Rahmen dieser Arbeit sollte ein bereits im Jahr 1989 gebauter Neutronenkollimator für den zukünftigen Einsatz an der Frankfurter Neutronenquelle am Stern Gerlach Zentrum (FRANZ) getestet und simuliert werden.
Hierfür wurde der Neutronenkollimator zunächst probeweise aufgebaut und die einzelnen Bauteile ausgemessen. Zunächst wurde die Zusammensetzung der Kollimatorbauteile überprüft und deren Dichte bestimmt. Zu diesem Zweck wurde mit einigen ausgesuchten Bauteilen des Kollimators eine Gammatransmissionsmessung mit Na-22 und Ba-133 als Gammaquelle durchgeführt. Die Messwerte dieser Messung wurden ausgewertet und mit entsprechend angefertigten Simulationen mit GEANT 3 verglichen.
Für die Simulationen wurden die Bauteile, mit denen die Messung durchgeführt wurde, detailgetreu und mit der zu bestätigenden Zusammensetzung sowie einer geschätzten Dichte programmiert. Über die Anpassung der Simulationsergebnisse an die experimentellen Werte, konnte so die Materialzusammensetzung bestätigt und für die jeweiligen Bauteile jeweils eine Dichte ermittelt werden. Für das Lithiumcarbonatrohr wurde eine Dichte von 1,422 g/cm³ ermittelt, für die drei Bauteile aus Borcarbid jeweils 1,169 g/cm³, 1,073 g/cm³, 0,832 g/cm³. Aufgrund von vielen produktionsbedingten, unterschiedlich stark ausgeprägten Lufteinschlüsse in den Borcarbidbauteilen des Kollimators, konnte keine identische Dichte für alle Bauteile gefunden werden.
Nach Untersuchung des Kollimators wurde der Neutronendurchgang mit dem Simulationspaket GEANT 3 simuliert. Die vollständige Geometrie des Kollimators wurde in GEANT 3 programmiert und dabei Bohrlöcher und Besonderheiten einzelner Bauteile berücksichtigt. Um die Simulationszeit zu verkürzen, wurde der Teilchendurchgang durch den gesamten Kollimator nicht in einem Durchgang simuliert, sondern stückweise in vier Stufen entlang des Kollimators. Um die Komplexität der Simulation zu beschränken wurde für alle Kollimatorbauteile aus Borcarbid ein Dichtewert eingesetzt, jedoch jede Simulationsreihe mit den drei verschiedenen Werten, die bei der Gammatransmissionsmessung ermittelt wurden, durchgeführt.
Beim anschließenden Vergleich der Simulationsergebnisse, konnte zwischen den einzelnen Dichtewerten kein signifikanter Unterschied erkannt werden. Die Unsicherheiten in der Dichtebestimmung sind daher vernachlässigbar.
Jede Simulationsreihe wurde mit zwei verschiedenen Neutronenverteilungen durchgeführt: eine Neutronenverteilung bei 1,92 MeV Protonenenergie und eine bei 2 MeV Protonenenergie.
Anhand der Simulationsergebnisse konnte ermittelt werden, dass die auf den Detektor eintreffende Neutronenintensität bis zu einem Abstand von etwa 20 cm vom Strahlachsenzentrum um Faktor 4·10-5 geschwächt wird. Ab 20 cm Strahlachsenabstand beträgt die Transmission der Neutronen etwa 10-3.
Die Bleiabschirmung, die an den Kollimator montiert wird und den Detektor vor den infolge von Neutroneneinfängen emittierten Gammaquanten vor dem Detektor abschirmen soll, reduziert die Zahl der Gammaquanten ebenfalls um Faktor 10-4.
Für den zukünftigen Einsatz des Neutronenkollimators an FRANZ müssen zunächst die fehlenden Kollimatorbauteile ersetzt oder nachgebaut werden. Dazu gehören zwei zylinderförmige innere Einsätze aus Borcarbid sowie eine Verlängerung des Innenrohrs aus Lithiumcarbonat. Neue Geometrien oder Materialzusammensetzungen können durch leichte Modifikation der bereits in GEANT 3 programmierten Kollimator-geometrie getestet und untersucht werden.
Für die Positionierung des Kollimators und Aufstellung vor dem 4 π BaF2-Detektor muss zusätzlich eine Platte angefertigt werden, an welche die Bleiabschirmung montiert und auf welcher der Kollimator stabil aufgebaut werden kann. Nach Fertigstellung der fehlenden Bauteile und der Platte, kann der Kollimator aufgebaut und in der Praxis getestet werden.
The ( J, T ) = (1, 1) parity doublet in 20Ne at 11.26 MeV is a good candidate to study parity violation in nuclei. However, its energy splitting is known with insufficient accuracy for quantitative estimates of parity violating effects. To improve on this unsatisfactory situation, nuclear resonance fluorescence experiments using linearly and circularly polarized γ -ray beams were used to determine the energy difference of the parity doublet E = E(1−) − E(1+) = −3.2(±0.7)stat( +0.6 −1.2)sys keV and the ratio of their integrated cross sections I (+) s,0 /I (−) s,0 = 29(±3)stat( +14 −7 )sys. Shell-model calculations predict a parityviolating matrix element having a value in the range 0.46–0.83 eV for the parity doublet. The small energy difference of the parity doublet makes 20Ne an excellent candidate to study parity violation in nuclear excitations.
In this work we study basic properties of unstable particles and scalar hadronic resonances, respectively, within simple quantum mechanical and quantum field theoretical (effective) models. The term 'particle' is usually assigned to entities, described by physical theories, that are able to propagate over sufficiently large time scales (e.g. from a source to a detector) and hence could be identified in experiments - one especially should be able to measure some of their distinct properties like spin or charge. Nevertheless, it is well known that there exists a huge amount of unstable particles to which it seems difficult to allocate such definite values for their mass and decay width. In fact, for extremely short-lived members of that species, so called resonances, the theoretical description turns out to be highly complicated and requires some very interesting concepts of complex analysis.
In the first chapter, we start with the basic ideas of quantum field theory. In particular, we introduce the Feynman propagator for unstable scalar resonances and motivate the idea that this kind of correlation function should possess complex poles which parameterize the mass and decay width of the considered particle. We also brie
y discuss the problematic scalar sector in particle physics, emphasizing that hadronic loop contributions, given by strongly coupled hadronic intermediate states, dominate its dynamics. After that, the second chapter is dedicated to the method of analytic continuation of complex functions through branch cuts. As will be seen in the upcoming sections, this method is crucial in order to describe physics of scalar resonances because the relevant functions to be investigated (namely, the Feynman propagator of interacting quantm field theories) will also have branch cuts in the complex energy plane due to the already mentioned loop contributions. As is consensus among the physical community, the understanding of the physical behaviour of resonances requires a deeper insight of what is going on beyond the branch cut. This will lead us to the idea of a Riemann surface, a one-dimensional complex manifold on which the Feynman propagator is defined.
We then apply these concepts to a simple non-relativistic Lee model in the third chapter and demonstrate the physical implications, i.e., the motion of the propagator poles and the behaviour of the spectral function. Besides that, we investigate the time evolution of a particle described by such a model. All this will serve as a detailed preparation in order to encounter the rich phenomena occuring on the Riemann surface in quantum field theory. In the last chapter, we finally concentrate on a simple quantm field theoretical model which describes the decay of a scalar state into two (pseudo)scalar ones. It is investigated how the motion of the propagator poles is in
uenced by loop contributions of the two (pseudo)scalar particles. We perform a numerical study for a hadronic system involving a scalar seed state (alias the σ-meson) that couples to pions. The unexpected emergence of a putative stable state below the two-pion threshold is investigated and it is claeifieed under which conditions such a stable state appears.
Das Schwerionenkollisionen Programm der Beschleuniger RHIC und LHC gibt Hinweise auf einen neuen Zustand hadronischer Materie --- das Quark-Gluon Plasma. Dieses zeichnet sich durch eine zumindest partielle Aufhebung des confinements aus, welches besagt, dass keine freien Quarks beochtbar sind.
Aus einer Beschreibung der experimentellen Daten mit relativistischer Hydrodynamik folgen weitere Eigenschaften. So geht das in einer Schwerionenkollision erzeugte Quark-Gluon Plasma nach sehr kurzer Zeit, etwa 1 fm/c, in ein zumindest lokales thermisches Gleichgewicht über. Durch die Lorentzkontraktion der beiden Schwerionen erwartet man, dass der Zustand direkt nach der Kollision durch eine Impulsanisotropie in der transversal-longitudinalen Ebene bestimmt wird. Somit setzt das Erreichen eines thermischen Gleichgewichts zunächst eine Isotropisierung voraus. Bisherige Studien haben gezeigt, dass gluonische Moden bei dieser Isotropisierung durch Verursachung einer chromo-Weibel Instabilität eine entscheidende Rolle spielen.
Weiterhin verhält sich das Quark-Gluon Plasma wie eine fast perfekte Flüssigkeit. Eine Berücksichtigung dissipativer Terme in der hydrodynamischen Beschreibung erfordert das Hinzufügen weiterer Terme zu den entsprechenden Bewegungsgleichungen. Diese sind proportional zu Transportkoeffizienten, welche durch die zugrunde liegende mikroskopische Theorie festgelegt sind.
Diese Theorie ist Quantenchromodynamik. Sie beschreibt die starke Wechselwirkung der Quarks und Gluonen und ist ein fundamentaler Baustein des Standardmodells der Teilchenphysik. Da im Regelfall Prozesse der starken Wechselwirkung nichtperturbativ sind, beschreiben wir QCD unter Verwendung einer Gitterregularisierung. Diese beruht auf einer Diskretisierung der vierdimensionalen Euklidischen Raumzeit durch einen Hyperkubus mit periodischen Randbedingungen und ermöglicht ein Lösen der QCD mit numerischen Methoden. Allerdings ist die Anwendung der Gittereichtheorie auf Systeme im thermischen Gleichgewicht beschränkt und kann somit keine Prozesse beschreiben, die auf Echtzeit basieren.
Transportkoeffizienten entsprechen Proportionalitätskoeffizienten, die die Relaxation einer Flüssigkeit oder eben eines Quark-Gluon Plasmas von einer kleinen Störung beschreiben. Damit sind sie unmittelbar mit der Zeit verknüpft. Über Kubo-Formeln lassen sie sich jedoch mit Gleichgewichtserwartungswerten retardierter Korrelatoren verknüpfen und werden so in Gitter QCD zugänglich.
In der vorliegenden Dissertation berechnen wir den Transportkoeffizienten κ in Gittereichtheorie für das Yang-Mills Plasma. Dabei nutzen wir aus, dass dieser Transportkoeffizient eine triviale analytische Fortsetzung vom retardierten zum Euklidischen Korrelator besitzt, welcher direkt in Gittereichtheorie zugänglich ist. Es ist die erste nichtperturbative Berechnung eines Transportkoeffizienten in QCD ohne weitere Annahmen, wie die Maximum Entropie Methode oder Ansätze, zu treffen.
XIII Nuclei in the Cosmos, 7-11 July, 2014 Debrecen, Hungary.
As an alternative production scenario to the so-called g process, the most abundant p nucleus 92Mo may be produced by a chain of proton-capture reactions in supernovae type Ia. The reactions 90Zr(p,g) and 91Nb(p,g) are the most important reactions in this chain. We have measured the first reaction using high-resolution in-beam g-spectroscopy at HORUS, Cologne, Germany, to contribute to the existing experimental data base. So far, we only investigated the high-energy part of the Gamow window and the analysis is still in progress. We plan to study the second reaction in standard kinematics at the FRANZ facility, Frankfurt, Germany. Current developments at FRANZ will be explained in detail.
Ziel dieser Arbeit war, mittels einer (n,γ)-Aktivierung, 129Te zu erzeugen und eine Teilchenzahlbestimmung durchzuführen. Aktivierung der Probe am Forschungsreaktor TRIGA und Spektrenaufnahme mittels eines HPGe-Detektors erfolgten im Mai 2014 am Institut für Kernchemie der Johannes Gutenberg Universität in Mainz.
Die Teilchenzahl des Tochternuklids 129I kann anhand der Teilchenzahlen des Isomers und des Grundzustandes von 129Te berechnet werden. In den Aktivierungen #2 bis #6 wurden (14.27 ± 0.53)x10exp12 Iodnuklide erzeugt. Angegeben ist die maximal mögliche Anzahl von Iodteilchen bei unendlich langer Wartezeit und vollständigem Zerfall aller Tellurnuklide.
Beobachtet werden konnte die Abnahme der Grundzustandsaktivität bis zum Erreichen des Gleichgewichts aus Nachbevölkerung durch das Isomer und Zerfall. Die Grundzustandslinien der Energien von 459.60 keV, 487 keV, 1083 KeV und 1111 keV konnten zu dieser Untersuchung herangezogen werden. Diese 4 Linien erfüllen die erforderten Konsistenzkriterien bezüglich der Systematik und können daher zur Teilchenzahlbestimmung des Grundzustandes verwendet werden (Seite 31).
Der Einfluss der Eigenabsorption ist noch zu untersuchen, da die genaue Position der Probe im Polyethylenbehältnis nicht bestimmt werden konnte. Weiterhin ist die Datenanalyse der ersten Aktivierung aufgrund des Detektorwechsels noch nicht erfolgt. Der Austausch war wegen technischer Probleme notwendig. Ziel weiterführender Untersuchungen ist, eine erneute Halbwertszeitbestimmung des radioaktiven 129I vorzunehmen. Sie ist von Interesse, angesichts des Widerspruchs zweier Veröffentlichungen. Die Halbwertszeit des 129I kann Aufschluss über stellare Bedingungen des s-Prozesses geben.
We report on the production of inclusive Υ(1S) and Υ(2S) in p-Pb collisions at sNN−−−√=5.02 TeV at the LHC. The measurement is performed with the ALICE detector at backward (−4.46<ycms<−2.96) and forward (2.03<ycms<3.53) rapidity down to zero transverse momentum. The production cross sections of the Υ(1S) and Υ(2S) are presented, as well as the nuclear modification factor and the ratio of the forward to backward yields of Υ(1S). A suppression of the inclusive Υ(1S) yield in p-Pb collisions with respect to the yield from pp collisions scaled by the number of binary nucleon-nucleon collisions is observed at forward rapidity but not at backward rapidity. The results are compared to theoretical model calculations including nuclear shadowing or partonic energy loss effects.
We report on the production of inclusive Υ(1S) and Υ(2S) in p-Pb collisions at sNN−−−√=5.02 TeV at the LHC. The measurement is performed with the ALICE detector at backward (−4.46<ycms<−2.96) and forward (2.03<ycms<3.53) rapidity down to zero transverse momentum. The production cross sections of the Υ(1S) and Υ(2S) are presented, as well as the nuclear modification factor and the ratio of the forward to backward yields of Υ(1S). A suppression of the inclusive Υ(1S) yield in p-Pb collisions with respect to the yield from pp collisions scaled by the number of binary nucleon-nucleon collisions is observed at forward rapidity but not at backward rapidity. The results are compared to theoretical model calculations including nuclear shadowing or partonic energy loss effects.
Transverse momentum spectra of π±, K± and p(p¯) up to pT = 20 GeV/c at mid-rapidity in pp, peripheral (60–80%) and central (0–5%) Pb–Pb collisions at √sNN = 2.76 TeV have been measured using the ALICE detector at the Large Hadron Collider. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at pT ≈ 3 GeV/c in central Pb–Pb collisions. Below the peak, pT < 3 GeV/c, both ratios are in good agreement with hydrodynamical calculations, suggesting that the peak itself is dominantly the result of radial flow rather than anomalous hadronization processes. For pT > 10 GeV/c particle ratios in pp and Pb–Pb collisions are in agreement and the nuclear modification factors for π±, K± and p(p¯) indicate that, within the systematic and statistical uncertainties, the suppression is the same. This suggests that the chemical composition of leading particles from jets in the medium is similar to that of vacuum jets.
Transverse momentum spectra of π±, K± and p(p¯) up to pT = 20 GeV/c at mid-rapidity in pp and Pb-Pb collisions at sNN−−−√= 2.76 TeV have been measured using the ALICE detector at the Large Hadron Collider. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at pT≈3GeV/c in central Pb-Pb collisions. Below the peak, pT < 3 GeV/c, both ratios are in good agreement with hydrodynamical calculations, suggesting that the peak itself is dominantly the result of radial flow rather than anomalous hadronization processes. For pT > 10 GeV/c particle ratios in pp and Pb-Pb collisions are in agreement and the nuclear modification factors for π±, K± and p(p¯) indicate that, within the systematic and statistical uncertainties, the suppression is the same. This suggests that the chemical composition of leading particles from jets in the medium is similar to that of vacuum jets.
Oscillations play a critical role in cognitive phenomena and have been observed in many brain regions. Experimental evidence indicates that classes of neurons exhibit properties that could promote oscillations, such as subthreshold resonance and electrical gap junctions. Typically, these two properties are studied separately but it is not clear which is the dominant determinant of global network rhythms. Our aim is to provide an analytical understanding of how these two effects destabilize the fluctuation-driven state, in which neurons fire irregularly, and lead to an emergence of global synchronous oscillations. Here we show how the oscillation frequency is shaped by single neuron resonance, electrical and chemical synapses.The presence of both gap junctions and subthreshold resonance are necessary for the emergence of oscillations. Our results are in agreement with several experimental observations such as network responses to oscillatory inputs and offer a much-needed conceptual link connecting a collection of disparate effects observed in networks.
In this thesis hard probes are studied in the partonic transport model BAMPS (Boltzmann Approach to MultiParton Scatterings). Employing Monte Carlo techniques, this model describes the 3+1 dimensional evolution of the quark gluon plasma phase in ultra-relativistic heavy-ion collisions by propagating all particles in space and time and carrying out their collisions according to the Boltzmann equation. Since hard probes are produced in hard processes with a large momentum transfer, the value of the running coupling is small and their interactions should be describable within perturbative QCD (pQCD). This work focuses on open heavy flavor, but also addresses the suppression of light parton jets, in particular to highlight differences due to the mass. For light partons, radiative processes are the dominant contribution to their energy loss. For heavy quarks, we show that also binary interactions with a running coupling and an improved Debye screening matched to hard-thermal-loop calculations play an important role. Furthermore, the impact of the mass in radiative interactions, prominently named the dead cone effect, and the interplay with the Landau-Pomeranchuk-Migdal (LPM) effect are studied in great detail. Since the transport model BAMPS has access to all medium properties and the space time information of heavy quarks, it is the ideal tool to study the dissociation and regeneration of J/psi mesons, which is also investigated in this thesis.
In the framework of an interference setup in which only two outcomes are possible (such as in the case of a Mach–Zehnder interferometer), we discuss in a simple and pedagogical way the difference between a standard, unitary quantum mechanical evolution and the existence of a real collapse of the wavefunction. This is a central and not-yet resolved question of quantum mechanics and indeed of quantum field theory as well. Moreover, we also present the Elitzur–Vaidman bomb, the delayed choice experiment, and the effect of decoherence. In the end, we propose two simple experiments to visualize decoherence and to test the role of an entangled particle.
The Facility for Antiproton and Ion Research (FAIR), under construction at Darmstadt will provide intense relativistic beams of exotic nuclei at its Superconducting-FRagment Separator. High-resolution in-beam γ-ray spectroscopy will be performed in the HISPEC experiment, using the European Advanced GAmma-ray Tracking Array (AGATA). The PreSPEC-AGATA campaign is the predecessor of HISPEC and runs from 2012 to 2014 at GSI Helmholtzzentrum für Schwerionenforschung GmbH. Up to19 AGATA modules were used at GSI's F Ragment Separator in 2012. We report on the status of the experiment including preliminary results from performance commissioning.
In dieser Arbeit wird der Strahltransport in einem CH-Driftröhrenbeschleuniger untersucht. Hierfür wurden numerische Simulationen zur elektromagnetischen Feldverteilung und dem strahldynamischen Einfluss der CH-Driftröhrenkavität durchgeführt. Sie fungiert als Prototyp für CH-Strukturen im Injektor des MYRRHA-Projekts, einem beschleunigergetriebenen System (ADS) zur Transmutation radioaktiven Abfalls. Zudem wird sie an der im Aufbau befindlichen Frankfurter Neutronenquelle am Stern-Gerlach-Zentrum (FRANZ) an der Goethe-Universität Frankfurt am Main experimentell mit Strahl getestet werden. FRANZ dient neben dem Einsatz als Experimentierfeld für neuartige Beschleuniger- und Strahldiagnostikkonzepte vor allem der Forschung im Bereich nuklearer Astrophysik.
This thesis presents experimental studies of proton capture and fragmentation reactions with heavy-ion storage rings. In one experiment, the 96Ru(p, γ)97Rh cross sections near the Gamow window have been measured at the ESR of GSI. In the other experiment, the measurement of the fragmentation yields has been carried out at the CSRe of IMP.
It is essential to determine the cross sections of (γ, p) or (p, γ) reactions for p-process network calculations. However, only very few of the required cross sections have been measured and thus most of them rely solely on Hauser-Feshbach model predictions. The predictions of the model have always very large uncertainties because of the not well-known input parameters. These parameters can be constrained by experiments. Compared to the traditional activation technique, a novel method using a storage ring has been developed to measure the cross sections of (p, γ) reactions in inverse kinematics.
This proton capture experiment has been performed at the ESR, where the circulating 96Ru44+ ions interacted with a hydrogen gas target at 9, 10 and 11 MeV/u. The nuclear reaction products of (p, p), (p, α), (p, n) and (p, γ) reactions were registered by position sensitive detectors. A Geant4 simulation code has been developed to distinguish the (p, γ) reaction products unambiguously from the background reactions. In this work, a relative normalization method has been utilized to accurately determine the cross sections of the (p, γ) reaction. The 96Ru(p, γ)97Rh cross section in the Gamow window of the p process is sensitive to two parameters, i.e., the γ-ray strength function and the optical model potential, while it is mainly sensitive to the γ-ray strength function in the energy region of our experiment. Therefore, our experimental (p, γ) cross sections near 10 MeV/u have been used to directly constrain the γ-ray strength function used in the model. Furthermore, the proton potential has also been constrained by combining our results with additional experimental data for this reaction in the lower energy region. The constrained model has been used to calculate the reaction rate over a wide temperature range, which is an extremely important input for astrophysical calculations.
The yields of fragments produced by 78Kr fragmentation reactions have been measured at the CSRe for the Tz = −1/2 and Tz = 1/2 nuclei along or close to the paths of αp- and rp-processes. The measured yields present a significant odd-even staggering effect for Tz = −1/2 nuclides but they are small for Tz = 1/2 nuclides.
The magnitude of this effect for four consecutive yields has been quantified using a third-order difference formula. It is found that the largest odd-even staggering is reached near the closed shells Z = 20 and Z = 28. Our experimental results could also compared with the data from other experiments with different projectile-target combinations. All these experimental data strongly support the closed shells Z = 20 and Z = 28 for the Tz = −1/2 nuclei.
The HADES collaboration has searched for the anti-kaonic nuclear cluster “ppK−” in p+p collisions by its decay into pΛ. In the course of this analysis several cross checks had to be performed. This report discusses two examples thereof. In one test it was checked whether the presence of background events could introduce a bias on the applied partial wave analysis. The second item discussed here is the extraction of the total pK+Λ production cross section necessary to derive the absolute upper limit on the “ppK−” production cross section.
The ALICE Zero Degree Calorimeter system (ZDC) is composed of two identical sets of calorimeters, placed at opposite sides with respect to the interaction point, 114 meters away from it, complemented by two small forward electromagnetic calorimeters (ZEM). Each set of detectors consists of a neutron (ZN) and a proton (ZP) ZDC. They are placed at zero degrees with respect to the LHC axis and allow to detect particles emitted close to beam direction, in particular neutrons and protons emerging from hadronic heavy-ion collisions (spectator nucleons) and those emitted from electromagnetic processes. For neutrons emitted by these two processes, the ZN calorimeters have nearly 100% acceptance.
During the √sNN = 2.76 TeV Pb-Pb data-taking, the ALICE Collaboration studied forward neutron emission with a dedicated trigger, requiring a minimum energy deposition in at least one of the two ZN. By exploiting also the information of the two ZEM calorimeters it has been possible to separate the contributions of electromagnetic and hadronic processes and to study single neutron vs. multiple neutron emission.
The measured cross sections of single and mutual electromagnetic dissociation of Pb nuclei at √sNN = 2.76 TeV, with neutron emission, are σsingle EMD = 187:4 ± 0.2 (stat.)−11.2+13.2 (syst.) b and σmutual EMD = 5.7 ± 0.1 (stat.) ±0.4 (syst.) b, respectively [1]. This is the first measurement of electromagnetic dissociation of 208Pb nuclei at the LHC energies, allowing a test of electromagnetic dissociation theory in a new energy regime. The experimental results are compared to the predictions from a relativistic electromagnetic dissociation model.
The study of neutron-induced reactions is of high relevance in a wide variety of fields, ranging from stellar nucleosynthesis and fundamental nuclear physics to applications of nuclear technology. In nuclear energy, high accuracy neutron data are needed for the development of Generation IV fast reactors and accelerator driven systems, these last aimed specifically at nuclear waste incineration, as well as for research on innovative fuel cycles. In this context, a high luminosity Neutron Time Of Flight facility, n_TOF, is operating at CERN since more than a decade, with the aim of providing new, high accuracy and high resolution neutron cross-sections. Thanks to the features of the neutron beam, a rich experimental program relevant to nuclear technology has been carried out so far. The program will be further expanded in the near future, thanks in particular to a new high-flux experimental area, now under construction.
Fast nuclei are ionizing radiation which can cause deleterious effects to irradiated cells. The modelling of the interactions of such ions with matter and the related effects are very important to physics, radiobiology, medicine and space science and technology. A powerful method to study the interactions of ionizing radiation with biological systems was developed in the field of microdosimetry. Microdosimetry spectra characterize the energy deposition to objects of cellular size, i.e., a few micrometers.
In the present thesis the interaction of ions with tissue-like media was investigated using the Monte Carlo model for Heavy-Ion Therapy (MCHIT) developed at the Frankfurt Institute for Advanced Studies. MCHIT is a Geant4-based application intended to benchmark the physical models of Geant4 and investigate the physical properties of therapeutic ion beams. We have implemented new features in MCHIT in order to calculate microdosimetric quantities characterizing the radiation fields of accelerated nucleons and nuclei. The results of our Monte Carlo simulations were compared with recent experimental microdosimetry data.
In addition to microdosimetry calculations with MCHIT, we also investigated the biological properties of ion beams, e.g. their relative biological effectiveness (RBE), by means of the modified Microdosimetric-Kinetic model (MKM). The MKM uses microdosimetry spectra in describing cell response to radiation. MCHIT+MKM allowed us to study the physical and biological properties of ion beams. The main results of the thesis are as follows:
MCHIT is able to describe the spatial distribution of the physical dose in tissue-like media and microdosimetry spectra for ions with energies relevant to space research and ion-beam cancer therapy; MCHIT+MKM predicts a reduction of the biological effectiveness of ions propagating in extended medium due to nuclear fragmentation reactions; We predicted favourable biological dose-depth profiles for monoenergetic helium and lithium beams similar to the one for carbon beam. Well-adjusted biological dose distributions for H-1, He-4, C-12 and O-16 with a very flat spread-out Bragg peak (SOBP) plateau were calculated with MCHIT+MKM; MCHIT+MKM predicts less damage to healthy tissues in the entrance channel for SOBP He-4 and C-12 beams compared to H-1 and O-16 ones. No definitive advantages for oxygen ions with respect to carbon were found.