Magnetism in ultracold quantum gases

Abstract

We study the static and dynamic magnetic properties of ultracold quantum gases, in particular the spinor physics of F = 1 and F = 2 Bose-Einstein condensates of ⁸⁷Rb atoms. Our data lead to the conclusion, that the F = 2 ground state of ⁸⁷Rb is polar, while we find the F = 1 ground state to be ferromagnetic. The dynamics of spinor systems is linked to an interplay between coherent mean-field interactions, losses and interactions with atoms in the thermal cloud. Within this rich parameter space we observe indications for coherent spinor dynamics and novel thermalization regimes.     

Coupling of a Liquid Organic Hydrogen Carrier System with Industrial Heat

Energy storage is needed for adjusting fluctuating renewable energies to the actual energy demand. A liquid organic hydrogen carrier (LOHC) system is examined for its suitability as a storage system for industrial applications. Integration of the LOHC system, e.g., into a cement plant allows for optimized utilization of waste heat. The exhaust heat from the cement plant can increase the efficiency of the storage system. The effectiveness of the LOHC system can be elevated by twelve percentage points. The working electricity costs of the cement plant can be significantly reduced by adding a LOHC storage system.     

Screening for the detection of angiotensin-converting enzyme inhibitors, their metabolites, and AT II receptor antagonists

A gas chromatography-mass spectrometry (GC-MS) screening procedure was developed for the detection of angiotensin-converting enzyme (ACE) inhibitors, their metabolites, and angiotensin (AT) II receptor antagonists in urine as part of a systematic toxicologic analysis procedure for acidic drugs and poisons after extractive methylation. The part of the phase-transfer catalyst remaining in the organic phase was removed by solid phase extraction on a diol phase. The compounds were separated by capillary GC and identified by computerized MS in the full scan mode. Using mass chromatography with the ions m/z 157, 160, 172, 192, 204, 220, 234, 248, 249, and 262, the possible presence of ACE inhibitors, their metabolites, and AT II antagonists could be indicated. The identity of positive signals in such mass chromatograms was confirmed by comparison of the peaks underlying full mass spectra with the reference spectra recorded during this study. This method allowed detection of therapeutic concentrations of ACE inhibitors (benazepril, enalapril, perindopril, quinapril, ramipril, trandolapril, their metabolites, or both) and therapeutic concentrations of the AT II antagonist, valsartan, in human urine samples. Human urine samples were not available for testing cilazapril, moexipril, and losartan; they were detected only in rat urine. The overall recoveries of ACE inhibitors ranged between 80% and 88%, with a coefficient of variation (CV) of less than 10% and the limit of detection of at least 10 ng/ml (signal to noise ratio 3) in the full-scan mode. The overall recovery of the valsartan was 68%, with a CV of less than 10%; the limit of detection was at least 10 ng/ml (S/N 3) in the full scan mode.     

Electron transfer dynamics of Rhodopseudomonas viridis reaction centers with a modified binding site for the accessory bacteriochlorophyll

Femtosecond spectroscopy in combination with site-directed mutagenesis was used to study the influence of histidine L153 in primary electron transfer in the reaction center of Rhodopseudomonas viridis. Histidine was replaced by cysteine, glutamate, or leucine. The exchange to cysteine did not lead to significant changes in the primary reaction dynamics. In the case of the glutamate mutation, the decay of the excited electronic level of the special pair P* is slowed by a factor of 3. The exchange to leucine caused the incorporation of a bacteriopheophytin b instead of a bacteriochlorophyll b molecule at the BA site. As a consequence of this chromophore exchange, the energy level of the electron transfer state P+BA- is lowered to such an extent that repopulation from the next electron transfer intermediate state P+HA- takes place, resulting in a long-lasting P+BA- population. The observed differences in time constants are discussed in the scope of nonadiabatic electron transfer theory considering the influence of the amino acids at position L153 and the chromophore exchange on the energy level of the intermediate state P+BA-. The results show that the high efficiency of primary electron transfer is reduced substantially, if the energy level of P+BA- is lowered or raised by several hundred wave numbers.     

Energetische Evaluierung von Kältespeichern und Abwärmenutzung für Kühl‐ und Gefrieranwendungen

A thermodynamic analysis of cold storage systems and waste heat usage for refrigeration and freezing applications is presented. The focus is set mainly on the energetic efficiency of the systems. The environment is considered as an infinite heat sink to which the heat from the refrigeration compartment can be transported directly. Five different concepts are presented and evaluated based on the annual electric energy and primary energy demand.     

In‐situ‐Stoffübergangsmessungen mit Computertomographie: Auswahl des Testsystems

For the in‐situ measurement of the mass transfer of a gas phase into a liquid film on a packing using X‐ray computed tomography, a substance combination is needed. The thickness of the liquid film was measured using computed tomography, to ensure that enough pixels in the film are available for the mass transfer experiments. In order to decide if the substance combination is distinguishable in the CT images, the X‐ray activity of gases and of dissolved gas in the liquid phase was investigated. For the determination of the maximum solubility the quantum chemical model COSMO‐RS was used to simulate the vapor‐liquid equilibria.     

Prediction of Equilibrium Partitioning of Nonpolar Organic Solutes in Water‐ Surfactant Systems by UNIFAC and COSMO‐RS Models

In the present study the potential of two thermodynamic‐based models (the group‐contribution UNIFAC model and the a priori predictive COSMO‐RS model) to predict solute partitioning in aqueous surfactant solutions is evaluated. In order to take into account the small size of micelles, the UNIFAC model was extended by the interfacial contribution based on the Gibbs‐Thompson equation. The applicability of the approach was successfully proved for the partitioning of nonpolar solutes (toluene, p‐xylene) in aqueous solutions of nonionic surfactants. The original COSMO‐RS model underestimates the concentration of the solute in the aqueous phase in the case of micellar systems since it does not account for the small size of micelles. At the same time, this model gives quantitative results for the octanol/water partition coefficients of both solutes under study leading to the conclusion that the affinity of both solutes to a certain solvent is well described. Thus, extending the COSMO‐RS by the interfacial term seems to be promising.     

Increasing the Equilibrium Yield of Oxidative Dehydrogenation with CO2 by Secondary Reactions

Oxidative dehydrogenation with carbon dioxide as an oxidant at low temperatures is strongly limited by its thermodynamic equilibrium. It is be shown that the equilibrium yield of the desired olefin can significantly be increased utilizing side reactions. This does not necessarily require the addition of another reactant, since this reactant can be formed in situ from the starting alkane. This effect allows for a decrease of the reaction temperature as well as the overall heat demand of the reaction. As a consequence, the exergy demand of the reaction system is reduced substantially.     

Innovative Verfahren mit komprimierten Gasen

By exploiting thermodynamic phenomena in systems with compressed gases, the properties of products such as their morphology and the size of particles and fibers can be tailored to industrial needs. Separation of complex mixtures can be accomplished. Processes that are conventionally operated in a number of costly steps can be reduced to a few operations. This article gives a phenomenological classification of such processes and explains the underlying principles. Operations developed on a laboratory scale as well as those already established in industry will be discussed.