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Institute
Infrared spectroscopy in combination with a specially developed attenuated total reflection (ATR) flow cell and multivariate analysis was used for the quantitative analysis of beer and other beverages. IR spectra of samples were obtained in the range from below 1000 cm-1 to 4000 cm-1 and subjected to a multivariate analysis based on calibration sets with laboratory reference standards. In the case of beer, this calibration set included 240 beer samples spanning the entire range of ethanol content, extract and CO2. Based on this calibration, an infrared and UV/Vis spectroscopy-based sensor for the quick and quantitative quality control of beer was developed and subjected to extensive tests in breweries. This sensor meets and exceeds all requirements from brewers for the routine control in the production and bottling. Its use for other beverages, for example wine, juices or apple wine, requires only another set of calibration data for the specific beverage.
We investigate the ratios βη≡η/τπ and βζ≡ζ/τΠ, i.e., the ratios of shear, η, and bulk, ζ, viscosities to the relaxation times τπ, τΠ of the shear stress tensor and bulk viscous pressure, respectively, in the framework of causal relativistic dissipative fluid dynamics. These viscous transport coefficients are computed both in a field-theoretical and a kinetic approach based on the Boltzmann equation. Our results differ from those of the traditional Boltzmann calculation by Israel and Stewart. The new expressions for the viscous transport coefficients agree with the results obtained in the field-theoretical approach when the contributions from pair annihilation and creation (PAC) are neglected. The latter induce non-negligible corrections to the viscous transport coefficients.
Using a microscopic transport model we investigate the evolution of conical structures originating from the supersonic projectile moving through the hot matter of ultrarelativistic particles. Using different scenarios for the interaction between projectile and matter, and different transport properties of the matter, we study the formation and structure of Mach cones. Especially, a dependence of the Mach cone angle on the details and rate of the energy deposition from projectile to the matter is investigated. Furthermore, the two-particle correlations extracted from the numerical calculations are compared to an analytical approximation. We find that the propagation of a high energetic particle through the matter does not lead to the appearance of a double peak structure as observed in the ultrarelativistic heavy-ion collision experiments. The reason is the strongly forward-peaked energy and momentum deposition in the head shock region. In addition, by adjusting the cross section we investigate the influence of the viscosity to the structure of Mach cones. A clear and unavoidable smearing of the profile depending on a finite ratio of shear viscosity to entropy density is clearly visible.
Driven by the loss of energy, isolated rotating neutron stars (pulsars) are gradually slowing down to lower frequencies, which increases the tremendous compression of the matter inside of them. This increase in compression changes both the global properties of rotating neutron stars as well as their hadronic core compositions. Both effects may register themselves observationally in the thermal evolution of such stars, as demonstrated in this Letter. The rotation-driven particle process which we consider here is the direct Urca (DU) process, which is known to become operative in neutron stars if the number of protons in the stellar core exceeds a critical limit of around 11% to 15%. We find that neutron stars spinning down from moderately high rotation rates of a few hundred Hertz may be creating just the right conditions where the DU process becomes operative, leading to an observable effect (enhanced cooling) in the temperature evolution of such neutron stars. As it turns out, the rotation-driven DU process could explain the unusual temperature evolution observed for the neutron star in Cas A, provided the mass of this neutron star lies in the range of 1.5 to 1.9M⊙ and its rotational frequency at birth was between 40 (400 Hz) and 70% (800 Hz) of the Kepler (mass shedding) frequency, respectively.
The spatial configuration of initial partons in high multiplicity proton–proton scatterings at 14 TeV is assumed as three randomly positioned “hot spots”. The parton momentum distribution in the hot spots is calculated by HIJING2.0 with some modifications. This initial condition causes not only large eccentricity ϵ2 but also triangularity ϵ3 and the correlation of ϵ2−ϵ3 event-plane angles. The final elliptic flow v2, triangular flow v3, and the correlation of v2−v3 event-plane angles are calculated by using the parton cascade model BAMPS to simulate the space–time parton evolution. Our results show that the v2−v3 correlation is different from that of ϵ2−ϵ3. This finding indicates that translations of different Fourier components of the initial spatial asymmetry to the final flow components are not independent. A dynamical correlation between the elliptic and triangular flow appears during the collective expansion.
We show from first principles the emergence of classical Boltzmann equations from relativistic nonequilibrium quantum field theory as described by the Kadanoff–Baym equations. Our method applies to a generic quantum field, coupled to a collection of background fields and sources, in a homogeneous and isotropic spacetime. The analysis is based on analytical solutions to the full Kadanoff–Baym equations, using the WKB approximation. This is in contrast to previous derivations of kinetic equations that rely on similar physical assumptions, but obtain approximate equations of motion from a gradient expansion in momentum space. We show that the system follows a generalized Boltzmann equation whenever the WKB approximation holds. The generalized Boltzmann equation, which includes off-shell transport, is valid far from equilibrium and in a time dependent background, such as the expanding universe.
We present, in the framework of the interacting hadron resonance gas, an evaluation of thermodynamical quantities. The interaction is modelled via a correction for the finite size of the hadrons. We investigate the sensitivity of the model calculations on the radius of the hadrons, which is a parameter of the model. Our calculations for thermodynamical quantities as energy and entropy densities and pressure are confronted with predictions using the lattice Quantum Chromodynamics (QCD) formalism.
Detailed knowledge of reaction mechanisms is key to understanding chemical, biological, and biophysical processes. For many reasons, it is desirable to comprehend how a reaction proceeds and what influences the reaction rate and its products.
In biophysics, reaction mechanisms provide insight into enzyme and protein function, the reason why they are so efficient, and what determines their reaction rates. They also reveal the relationship between the function of a protein and its structure and dynamics.
In chemistry, reaction mechanisms are able to explain side products, solvent effects, and the stereochemistry of a product. They are also the basis for potentially optimizing reactions with respect to yield, enhancing the stereoselectivity, or for modifying reactions in order to obtain other related products.
A key step to investigate reaction mechanisms is the identification and characterization of intermediates, which may be reactive, short-lived, and therefore only weakly populated. Nowadays, the structures of those can in most cases only be hypothesized based on products, side products, and isolable intermediates, because intermediates with a life time of less than a few microseconds are not accessible with the commonly used techniques for structure determination such as X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy.
In this thesis, two-dimensional infrared (2D-IR) spectroscopy is shown to be a powerful complement to the existing techniques for structure determination in solution. 2D-IR spectroscopy uses a femtosecond laser setup to investigate interactions between vibrations - analogous to 2D-NMR, which investigates the interactions between spins. Its ultrafast time resolution makes 2D-IR spectroscopy particularly well suited for the two topics investigated in this thesis: Structure Determination of Reactive Intermediates and Conformational Dynamics of Proteins.
Structure Determination of Reactive Intermediates: The focus of this thesis is using polarization-dependent 2D-IR (P2D-IR) spectroscopy for structure determination of N-crotonyloxazolidinone (referred to as 1), a small organic compound with a chiral oxazolidinone, known as Evans auxiliary, and its reactive complexes with the Lewis acids SnCl4 and Mg(ClO4)2. Chiral oxazolidinones in combination with Lewis acids have frequently been used in stereoselective synthesis for over 30 years. Nevertheless, the detailed mechanisms are in many cases xvi ABSTRACT still mere hypotheses and have not yet been experimentally proven. By accurately measuring the angles between the transition dipole moments in the molecules using an optimized P2D-IR setup and comparing the results to DFT calculations, the conformation of 1 and the conformation and coordination of the main complexes with SnCl4 and Mg(ClO4)2 are unequivocally identified and analyzed in depth. Structural details, such as a slight twist in the solution structure of 1, are detected using P2D-IR spectroscopy; these cannot be inferred from NMR spectroscopy or DFT calculations. In addition to the main Lewis acid complexes, complexes in low concentration are detected and tentatively assigned to different conformations and complexation geometries. The knowledge of those structures is essential for rationalizing the observed stereoselectivities. Additionally, a method is introduced that enables structure determination of molecules in complex mixtures and even in the presence of molecules with similar spectral properties and in high concentration. This work sets the stage for future studies of other substrate-catalyst complexes and reaction intermediates for which the structure determination has not been possible to date.
Conformational Dynamics of Proteins: Exchange 2D-IR spectroscopy allows the investigation of fast dynamics without disturbing the equilibrium of the exchanging species. It is therefore well suited to investigate fast dynamics of proteins and to reveal the speed limit of those. The temperature dependence of the conformational dynamics between the myoglobin substates A1 and A3 in equilibrium is analyzed. The various substates of myoglobin can be detected with FTIR spectroscopy, if carbon monoxide is bound to the heme. From previous studies it is known that the exchange rates at room temperature are in the picosecond time range, well suited to be investigated by 2D-IR spectroscopy. In the temperature range between 0 °C and 40 °C only a weak temperature dependence of the exchange rate in the myoglobin mutant L29I is observed in the present study. The exchange rate approximately doubles from 15 ns-1 at 0 °C to 31 ns-1 at 40 °C. It turned out that the conformational dynamics correlates linearly with the solvent viscosity, which itself is temperature dependent. Comparing our results to measurements at cryogenic temperatures, the linear relation between exchange time constant for this process and the viscosity is shown for the temperature range between -100 °C and 40 °C (corresponding to a viscosity change of 14 orders of magnitude). Thus, it is proven that the dynamics of the conformational switching are mainly determined by solvent dynamics, i.e., the protein dynamics are slaved to the solvent dynamics. This is the first time slaving is observed for such fast processes (in the picosecond time range). The observation implies a long-range structural rearrangement between the myoglobin substates A1 and A3. In addition, the exchange for other mutants and wild type myoglobin is analyzed qualitatively and found to agree with the conclusions drawn from L29I myoglobin.
In this thesis, various aspects on the theoretical description of ultracold bosonic atoms in optical lattices are investigated. After giving a brief introduction to the fundamental concepts of BECs, atomic physics, interatomic interactions and experimental procedures in chapter (1), we derive the Bose-Hubbard model from first principles in chapter (2). In this chapter, we also introduce and discuss a technique to efficiently determine Wannier states, which, in contrast to current techniques, can also be extended to inhomogeneous systems. This technique is later extended to higher dimensional, non-separable lattices in chapter (5). The many-body physics and phases of the Bose-Hubbard is shortly presented in chapter (3) in conjunction with Gutzwiller mean-field theory, and the recently devised projection operator approach. We then return to the derivation of an improved microscopic many-body Hamiltonian, which contains higher band contributions in the presence of interactions in chapter (4). We then move on to many-particle theory. To demonstrate the conceptual relations required in the following chapter, we derive Bogoliubov theory in chapter (5.3.4) in three different ways and discuss the connections. Furthermore, this derivation goes beyond the usual version discussed in most textbooks and papers, as it accounts for the fact, that the quasi-particle Hamiltonian is not diagonalizable in the condensate and the eigenvectors have to be completed by additional vectors to form a basis. This leads to a qualitatively different quasi-particle Hamiltonian and more intricate transformation relations as a result. In the following two chapters (7, 8), we derive an extended quasi-particle theory, which goes beyond Bogoliubov theory and is not restricted to weak interactions or a large condensate fraction. This quasi-particle theory naturally contains additional modes, such as the amplitude mode in the strongly interacting condensate. Bragg spectroscopy, a momentum-resolved spectroscopic technique, is introduced and used for the first experimental detection of the amplitude mode at finite quasi-momentum in chapter (9). The closely related lattice modulation spectroscopy is discussed in chapter (10). The results of a time-dependent simulation agree with experimental data, suggesting that also the amplitude mode, and not the sound mode, was probed in these experiments. In chapter (11) the dynamics of strongly interacting bosons far from equilibrium in inhomogeneous potentials is explored. We introduce a procedure that, in conjunction with the collapse and revival of the condensate, can be used to create exotic condensates, while particularly focusing on the case of a quadratic trapping potential. Finally, in chapter (12), we turn towards the physics of disordered systems derive and discuss in detail the stochastic mean-field theory for the disordered Bose-Hubbard model.
The study of systems whose properties are governed by electronic correlations is a corner stone of modern solid-state physics. Often, such systems feature unique and distinct properties like Mott metal-insulator transitions, rich phase diagrams, and high sensitivity to subtle changes in the applied conditions. Whereas the standard approach to electronic structure calculations, density functional theory (DFT), is able to address the complexity of real-world materials but is known to have serious limitations in the description of correlations, the dynamical mean-field theory (DMFT) has become an established method for the treatment of correlated fermions, first on the level of minimal models and later in combination with DFT, termed LDA+DMFT.
This thesis presents theoretical calculations on different materials exhibiting correlated physics, where we aim at covering a range in terms of systems --from rather weakly correlated to strongy correlated-- as well as in terms of methods, from DFT calculations to combined LDA+DMFT calculations. We begin with a study on a selection of iron pnictides, a recently discovered family of high-temperature superconductors with varying degree of correlation strength, and show that their magnetic and optical properties can be assessed to some degree within DFT, despite the correlated nature of these systems. Next, extending our analysis to the inclusion of correlations in the framework of LDA+DMFT, we discuss the electronic structure of the iron pnictide LiFeAs which we find to be well described by Fermi liquid theory with regard to many of its properties, yet we see distinct changes in its Fermi surface upon inclusion of correlations. We continue the study of low-energy properties and specifically Fermi surfaces on two more iron pnictides, LaFePO and LiFeP, and predict a topology change of their Fermi surfaces due to the effect of correlations, with possible implications for their superconducting properties. In our last study, we close the circle by presenting LDA+DMFT calculations on an organic molecular crystal on the verge of a Mott metal-insulator transition; there, we find the spectral and optical properties to display signatures of strong electronic correlations beyond Fermi liquid theory.