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We study equilibrium as well as out-of-equilibrium properties of the strongly interacting QGP medium under extreme conditions of high temperature T and high baryon densities or baryon chemical potentials μB within a kinetic approach. We present the thermodynamic and transport properties of the QGP close to equilibrium in the framework of effective models with Nf=3 active quark flavours such as the Polyakov extended Nambu-Jona Lasinio (PNJL) and dynamical quasiparticle model with the CEP (DQPM-CP). Considering the transport coefficients and the EoS of the QGP phase, we compare our results with various results from the literature. Furthermore, out-of equilibrium properties of the QGP medium and in particular, the effect of a μB- dependence of thermodynamic and transport properties of the QGP are studied within the Parton-Hadron-String-Dynamics (PHSD) transport approach, which covers the full evolution of the system during HICs. We find that bulk observables and flow coefficients for strange hadrons as well as for antiprotons are more sensitive to the properties of the QGP, in particular to the μB - dependence of the QGP interactions.
Presolar grain isotopic ratios as constraints to nuclear physics inputs for s-process calculations
(2023)
The isotopic abundances in presolar SiC grains of AGB origin provide important and precise constraints to those star nucleosynthesis models. By comparing the values of the s-element abundances resulting from calculations with the ones measured in these dust grains, it turns out that new measurements of weak-interaction rates in ionized plasmas, as well as of neutron-capture cross sections, are needed, especially in the region near the neutron magic numbers 50 and 82.
Results on proton and Λ flow, calculated with the UrQMD model that incorporates different realistic density dependent equations of state, are presented. It is shown that the proton and hyperon flow shows sensitivity to the equation of state and especially to the appearance of a phase transition at densities below 4n0. Even though qualitatively hyperons and protons exhibit the same beam energy dependence of the flow, the quantitative results are different. In this context it is suggested that the hyperon measurements can be used to study the density dependence of the hyperon interaction in high density QCD matter.
We introduce a novel technique that utilizes a physics-driven deep learning method to reconstruct the dense matter equation of state from neutron star observables, particularly the masses and radii. The proposed framework involves two neural networks: one to optimize the EoS using Automatic Differentiation in the unsupervised learning scheme; and a pre-trained network to solve the Tolman–Oppenheimer–Volkoff (TOV) equations. The gradient-based optimization process incorporates a Bayesian picture into the proposed framework. The reconstructed EoS is proven to be consistent with the results from conventional methods. Furthermore, the resulting tidal deformation is in agreement with the limits obtained from the gravitational wave event, GW170817.
We consider a linear ill-posed equation in the Hilbert space setting. Multiple independent unbiased measurements of the right-hand side are available. A natural approach is to take the average of the measurements as an approximation of the right-hand side and to estimate the data error as the inverse of the square root of the number of measurements. We calculate the optimal convergence rate (as the number of measurements tends to infinity) under classical source conditions and introduce a modified discrepancy principle, which asymptotically attains this rate.
A single wavelength heterodyne interferometer has been set up to investigate the free electron density integrated axially along the line of sight (line density) in a theta-pinch plasma to determine its applicability as a plasma target for ion beam stripping. The maximal line density reached in this experiment was (3.57 ± 0.28) × 1018 cm−2 at 80 Pa and 20 kV. The findings demonstrate the pulsed character of the line density and its increase by raising the load voltage and the working gas pressure. Additionally, the results were compared with spectroscopic free electron density estimations, which were carried out by Hβ -line broadening and peak separation. The time behavior of the line density indicates that its peak value is delayed by about 10 μs compared to the spectroscopic results. This effect is due to the formation of an extended, magnetically compressed plasma column in the vicinity of the current maximum, although the highest volumetric free electron density is reached near the current zero crossing. Since the line density is an essential parameter in describing the stripping capabilities of the plasma target, the interferometric diagnostic is superior to a spectroscopic diagnostic, because it directly provides integrated values along the line of sight. Furthermore, the measurements of the line density in this experiment partially show nonphysical negative values, which is due to gaseous effects and residual shot vibrations.
This thesis aims to investigate the properties of hadronic matter by analyzing fluctuations of conserved charges. A transport model (SMASH) is used for these studies to achieve this. The first part of this thesis focuses on examining transport coefficients, specifically the diffusion coefficients of conserved charges and the shear viscosity. The second part investigates equal-time correlations of particle numbers in the form of cumulants. The last chapter studies different aspects of the isobar collision systems Ru and Zr.
As a first step, the hadronic medium and interactions between its constituents are introduced, and simultaneously, their impact on transport coefficients is investigated. The methodology is verified by comparing the results of SMASH with Chapman-Enskog calculations, followed by examining 3-to-1 multi-particle reactions, revealing their influence on shear viscosity and electrical diffusion. The analysis of the full hadron gas considers angle-dependent cross-sections and additional elastic cross-sections via the AQM description, showing significant impacts on transport coefficients. The dependency on the number of degrees of freedom is explored, with noticeable effects on diffusion coefficients but a smaller influence on the shear viscosity. At non-zero baryon chemical potential, the diffusion coefficients are strongly influenced, while the shear viscosity remains unaffected. Overall, the study underscores the importance of individual cross-sections and the modeling of interactions on transport coefficients.
The following chapter explores fluctuations of conserved charges, crucial for understanding phase transitions in heavy-ion collision from the quark-gluon plasma to the hadronic phase. Using SMASH, the impact of global charge conservation on particle number cumulants in subvolumes of boxes simulating infinite matter is studied. Comparisons with simpler systems highlights the influence of hadronic interactions on cumulants, especially via charge annihilation processes and the results from SMASH shows agreement with analytical calculations. Calculations at finite baryon chemical potential reveals a transition from a Poisson to Skellam distribution within the net proton cumulants. It is shown that an unfolding procedure to obtain the net baryon fluctuations from the net proton ones deviates from the actual net baryon result, particularly in larger volumes. Finally, net proton correlations at vanishing baryon chemical potential align with ALICE measurements and the net proton cumulants are unaffected by deuteron formation.
In the next step, the goal is to investigate critical fluctuations in the hadronic medium. Therefore, the hadronic system is initialized with critical equilibrium fluctuations by coupling the hadron resonance gas with the 3D Ising model. The single-particle probability distributions are derived from the principle of maximum entropy. Evolving these distributions in SMASH, their development in an expanding sphere adjusted to experimental conditions can be analyzed. It reveals resonance decay and formations as the primary source that affects the particle cumulants. Because of isospin randomization processes, critical fluctuations are better preserved in net nucleon numbers. However, for the strongest coupling investigated in this work, correlations of the critical field are still present in the final state of the evolution in the net proton fluctuations. Examining cumulant dependence on rapidity windows shows a non-monotonic trend.
In the third part, collisions involving the isobars Ru and Zr are studied at a center-of-mass energy of 200 GeV. Initially, SMASH is used to study the initial conditions to hydrodynamical simulations, emphasizing the importance of the nuclear structure of isobars on the geometry of the collision area. It is found that the deformation parameters notably influence the initial state. Correlations between nucleon-nucleon pairs on eccentricity fluctuations yield no significant effect. Subsequently, the hydrodynamic model vHLLE evolves the previously explored initial conditions and for the transition between the hydrodynamic and kinetic descriptions, the Cooper-Frye formula is used. Usage of the canonical ensemble ensures the exact conservation of the conserved charges B, Q, and S. The neutron skin effect, which changes the charge distribution within Ru nuclei, is additionally considered. Fluctuations are assessed, revealing suppression in large rapidity windows due to global charge conservation. The hadronic phase modifies fluctuations of net pions, net kaons, and net protons via annihilation processes, yet fluctuations remain unaffected by the neutron skin effect.
Partial melting of crustal and mantle rocks under pressure from impedance spectroscopy measurements
(2004)
The purpose of this work is to achieve a better understanding of the physical properties of rocks during partial melting processes. The electrical conductivity of some crustal and upper mantle rocks was measured prior and above the melting under pressure. The variations of the electrical conductivity were compared with the distribution of melt in partially molten rock samples. The electrical conductivity was estimated from the impedance spectroscopy at temperatures between 800 and 1450˚C and at pressures between 0.3 and 2 GPa. These measurements were performed in a piston cylinder apparatus. At temperatures above the melting, samples were equilibrated during a long time and subsequently quenched. Thin sections were prepared and topology, volume fraction and chemical composition of melt was analyzed by using a microprobe. Above the solidus temperature, the electrical conductivity increases for about 1 to 2 orders of magnitude in comparison with non-melted rocks. The "melt effect" seems to reflect the formation of an interconnected network of melt. When a complete melt connectivity is established, the charge transport follows the network of the formed melt films at grain boundaries. Usually, it takes a long time in order to reach a steady state of the electrical resistance in partially molten rocks. Only when a steady state of the electrical resistance is achieved, the bulk conductivity of a sample can be measured properly. The time-independent electrical conductivity were found only after 200 h of annealing time at a desired temperature.
Usually, the measurements of a dihedral angle on grain-liquid interfaces in rocks show that the wetting of grain faces start to develop at temperatures slightly above the solidus temperature. The development of these faces should lead to a continuous melt network even at small melt fractions of few wt.%. This result is not confirmed by our electrical conductivity measurements. The complete interconnection of the melt phase, which was mark by an increase of the electrical conductivity, corresponds to a temperature significantly above the solidus temperature, for at least 30-50˚C. The development of these faces stimulate a significant increase of the electrical conductivity, and corresponds to the occurence of at least 5 wt.% of a melt fraction. This result could be explained by deviations from the textural equilibrium of a melt phase topology in partially molten samples due to heterogeneous grain size distribution, misorientation of grains and anisotropy of the superficial energy of adjacent grain boundaries.
Some mixing models that allow to calculate the electrical conductivity of a composite as a function of a melt fraction were examined and the results of these calculations are discussed.
The experimental results were compared to the conductivity data obtained from magnetotelluric and electromagnetic measurements in the Northern part of mid-Atlantic ridge where a series of magma chambers are presumably located. There is a good agreement between our conductivity values for a melt fraction of 10-13 the conductivity estimated in the Reykjanes ridge zone.
Das westphälische Modell für Staatsinstitutionen, einschließlich nationaler Exekutive, Legislative und Judikative, hat sich aus den Ereignissen europäischer Geschichte heraus entwickelt. Seit dem Ende des Kalten Krieges dient es als grundlegendes Paradigma für Internationale Interventionen zum Wiederaufbau von gescheiterten - oder zum Aufbau von neuen - Staaten. Für die internationale Gemeinschaft fungiert das westphälische Modell als Maß zur Beurteilung ihrer Interventionen, wie zum Beispiel in Somalia, Kambodscha oder den Balkanstaaten. In den meisten Fällen gilt eine durch sie beaufsichtigte oder gar durchgeführte ‚freie und faire’ Wahl als hauptsächliche Massnahme zur Bildung eines ‚westphälischen’ und demokratischen Staates. Die Erfolgsrate solcher internationalen Friedenseinsätze und ‚state-building operations’ ist jedoch enttäuschend. Bei näherer Betrachtung der Misserfolge des letzten Jahrzehnts wird deutlich, daß sich die lokalen Gesellschaftssysteme der betroffenen Bevölkerungen oft beträchtlich von liberaler Demokratie unterscheiden. Dies ist insbesondere der Fall in Gesellschaften deren Ordnung nicht auf Staatsinstiutionen basiert. Ihnen liegen sozio-politische Systeme zugrunde die sich oft mit dem Paradigma des westlichen Staatssystems nur schwer vereinen lassen. Um im Rahmen internationaler Friedenseinsätze erfolgreich Staatstrukturen zu etablieren, ist es daher notwendig lokale Sozialstrukturen und lokale Konzepte politischer Legitimität und Autorität zu addressieren. Erst mit solchem Verständnis ist es möglich einen Staatsapparat in den Augen der Bevölkerung zu legitimieren. Ist Letzteres nicht der Fall, so kann sich eine Regierung zwar in Übereinstimmung mit internationalen Menschenrechten befinden, oder alle wichtigen demokratischen Einrichtungen vorweisen, jedoch dennoch dem Prinzip der Partizipation durch die Bevölkerung widersprechen. Ist dies das Endresultat eines internationalen Friedenseinsatzes, so hat die internationale Gemeinschaft ihre eigenen Werte bestaetigt. Jedoch herrscht kein Vertrauen zwischen der Bevölkerung und Regierung, da letztere nicht kompatibel mit dem Versaendnis der Bürger ist. Der ‚demokratische’ Staat ist nur schwerlich funktionsfähig.Der internationale Einsatz in Osttimor illustriert dieses Problem. Hier wurden die Vereinten Nationen (VN) mit dem Wiederaufbau und der Verwaltung eines Staates betraut (UNTAET ‚Übergangsregierung der Vereinten Nationen in Osttimor’). Zum ersten mal in der Geschichte übernahm die international Gemeinschaft damit die Souveränität über ein territoriales Gebiet...