Observation of a Strong Atom-Dimer Attraction in a Mass-Imbalanced Fermi-Fermi Mixture

We investigate a mixture of ultracold fermionic $^{40}$K atoms and weakly bound $^{6}$Li$^{40}$K dimers on the repulsive side of a heteronuclear atomic Feshbach resonance. By radio-frequency spectroscopy we demonstrate that the normally repulsive atom-dimer interaction is turned into a strong attraction. The phenomenon can be understood as a three-body effect in which two heavy $^{40}$K fermions exchange the light $^{6}$Li atom, leading to attraction in odd partial-wave channels (mainly p-wave). Our observations show that mass imbalance in a fermionic system can profoundly change the character of interactions as compared to the well-established mass-balanced case

Probing Substituents in the 1- and 3-Position: Tetrahydropyrazino-Annelated Water-Soluble Xanthine Derivatives as Multi-Target Drugs With Potent Adenosine Receptor Antagonistic Activity

Tetrahydropyrazino-annelated theophylline (1,3-dimethylxanthine) derivatives have previously been shown to display increased water-solubility as compared to the parent xanthines due to their basic character. In the present study, we modified this promising scaffold by replacing the 1,3-dimethyl residues by a variety of alkyl groups including combinations of different substituents in both positions. Substituted benzyl or phenethyl residues were attached to the N8 of the resulting 1,3-dialkyl-tetrahydropyrazino[2,1-f ]purinediones with the aim to obtain multi-target drugs that block human A1 and A2A adenosine receptors (ARs) and monoaminoxidase B (MAO-B). 1,3-Diethyl-substituted derivatives showed high affinity for A1 ARs, e.g., 15d (PSB-18339, 8-m-bromobenzyl-substituted) displayed a Ki value of 13.6 nM combined with high selectivity. 1-Ethyl-3-propargyl-substituted derivatives exhibited increased A2A AR affinity. The 8-phenethyl derivative 20h was selective for the A2A AR (Ki 149 nM), while the corresponding 8-benzyl-substituted compound 20e (PSB-1869) blocked A1 and A2A ARs with equal potency (Ki A1, 180 nM; A2A, 282 nM). The 1-ethyl-3-methyl-substituted derivative 16a (PSB-18405) bearing a m,p-dichlorobenzyl residue at N8 blocked all three targets, A1 ARs (Ki 396 nM), A2A ARs (Ki 1,620 nM), and MAO-B (IC50 106 nM) with high selectivity vs. the other subtypes (A2B and A3 ARs, MAO-A), and can thus be considered as a multi-target drug. Our findings were rationalized by molecular docking studies based on previously published X-ray structures of the protein targets. The new drugs have potential for the treatment of neurodegenerative diseases, in particular Parkinson's disease

Judicial Review, Irrationality, and the Limits of Intervention by the Courts

When exercising judicial review, the courts, on occasions, have intervened in circumstances where administrative decisions were not irrational. However, these low standards of judicial intervention are arguably constitutional, especially since the enactment of the Human Rights Act 1998 (HRA). To this end, this article seeks to establish a zone of executive decision-making, for reasons of democracy, where the courts are clearly excluded. But it is unable to do so. Does this mean, therefore, that judicial intervention on the grounds of irrationality exists without limit? Assuming this to be the case, it is suggested that the courts should show greater respect to the administrative branch of the state where it has genuinely sought to engage with the legal process in arriving at its decisions

The GAAS Metagenomic Tool and Its Estimations of Viral and Microbial Average Genome Size in Four Major Biomes

Metagenomic studies characterize both the composition and diversity of uncultured viral and microbial communities. BLAST-based comparisons have typically been used for such analyses; however, sampling biases, high percentages of unknown sequences, and the use of arbitrary thresholds to find significant similarities can decrease the accuracy and validity of estimates. Here, we present Genome relative Abundance and Average Size (GAAS), a complete software package that provides improved estimates of community composition and average genome length for metagenomes in both textual and graphical formats. GAAS implements a novel methodology to control for sampling bias via length normalization, to adjust for multiple BLAST similarities by similarity weighting, and to select significant similarities using relative alignment lengths. In benchmark tests, the GAAS method was robust to both high percentages of unknown sequences and to variations in metagenomic sequence read lengths. Re-analysis of the Sargasso Sea virome using GAAS indicated that standard methodologies for metagenomic analysis may dramatically underestimate the abundance and importance of organisms with small genomes in environmental systems. Using GAAS, we conducted a meta-analysis of microbial and viral average genome lengths in over 150 metagenomes from four biomes to determine whether genome lengths vary consistently between and within biomes, and between microbial and viral communities from the same environment. Significant differences between biomes and within aquatic sub-biomes (oceans, hypersaline systems, freshwater, and microbialites) suggested that average genome length is a fundamental property of environments driven by factors at the sub-biome level. The behavior of paired viral and microbial metagenomes from the same environment indicated that microbial and viral average genome sizes are independent of each other, but indicative of community responses to stressors and environmental conditions

Radio-frequency spectroscopy on the mass-imbalanced 6Li-40K Fermi-Fermi mixture

Ultrakalte Quantengase sind ideale Systeme, um fundamentale Probleme sowohl der Vielteilchen- als auch der Mehrteilchen-Physik experimentell in Angriff zu nehmen. Die Parameter, die solche Systeme charakterisieren, können zu einem beispiellos hohen Grad an Präzision kontrolliert und ausgelesen werden. In dieser Arbeit werden Experimente mit Gemischen zweier Gase verschiedener fermionischer Atom-Spezies, 6Li und 40K, diskutiert. Unsere Untersuchungen können zwei größeren Forschungsthemen zugeordnet werden. Diese sind zum einen das grundlegende Vielteilchen-System, bestehend aus einem Fremdatom und einem Fermi-See, und zum anderen die Li-K Mehrteilchen-Physik. Um uns der Vielteilchen-Physik eines Fremdatoms im Fermi-See zu widmen, erzeugen wir ein Gemisch von wenigen K-Atomen und einer großen, dichten Wolke von Li-Atomen. Wir können die Wechselwirkung zwischen den Fremdatomen und den Atomen des Fermi-Sees mittels einer magnetischen Feshbach-Resonanz variieren. Wir führen dann Radiofrequenz-Spektroskopie an den Kalium-Atomen in mehreren Wechselwirkungsregimes, von stark repulsiv bis stark attraktiv, durch und legen so das Energiespektrum des Kalium-Atoms im Lithium-Fermi-See offen. Im stark wechselwirkenden Regime, wo die Streulänge größer ist als der Teilchenabstand, wird das Fremdatom, zusammen mit der Anregung des Fermi-Sees, Landaus Theorie der Fermi-Flüssigkeiten folgend, als Quasiteilchen beschrieben, das Polaron genannt wird. Wir bestimmen die Energie, das Residuum und die Lebensdauer der Polaronen in unserem System. Des Weiteren untersuchen wir die Dekohärenz der Fremdatome im Fermi-See als Funktion der Wechselwirkungsstärke, unter Verwendung einer Spin-Echo-Technik. Für mäßige Wechselwirkungsstärke stellen unsere Messungen eine Bestimmung der Quasiteilchen-Streurate dar. Bei nahresonanter Wechselwirkung bestimmen wir nahezu eine Größenordnung höhere Dekohärenzraten. In einer weiteren Messreihe untersuchen wir, auf Zeitskalen viel kürzer als die Fermi-Zeit, wie unser System auf ein rasch eingeführtes Fremdatom reagiert. Unter Verwendung einer Ramsey-Interferometrie-Technik verfolgen wir die Entstehung von repulsivem und attraktivem Polaron in Echtzeit. Bei resonanter Wechselwirkung beobachten wir die Quanteninterferenz, die durch gleichzeitiges Anregen des repulsiven und attraktiven Vielteilchen-Zweiges zustande kommt. Für die Untersuchungen der Physik in Li-K Mehrteilchen-Systemen erzeugen wir dichte Li-KDimerproben aus einem beinahe ausgewogenen Gemisch von Li- und K-Atomen. Wir führen dann Radiofrequenz-Spektroskopie durch, um die elastische Wechselwirkung zwischen K Atomen und Li-K-Dimeren zu untersuchen. Im Gegensatz zur Atom-Dimer-Wechselwirkung in einem Gemisch zweier Gase gleichschwerer fermionischer Atome, zeigen unsere Messungen eine starke K-LiK-Anziehung in einem Regime, wo sich Li- und K-Atome gegenseitig abstoßen. Die beobachtete Atom-Dimer-Anziehung in unserem Gemisch soll es vereinfachen, exotische Vielteilchenzustände und -phasen experimentell zu realisieren. Ob es möglich ist, solche Phasen experimentell zu realisieren, hängt stark von der Lebensdauer des Atom-Dimer-Gemischs ab, die typischer Weise durch die Dimer-Lebensdauer begrenzt ist. Daher untersuchen wir die Lebensdauer von Dimer-Wolken als Funktion der magnetischen Verstimmung von einer Feshbach-Resonanz. In unseren Messungen können wir zwischen verschiedenen Beiträgen zum Zerfall einer Dimerprobe unterscheiden und wir erhalten die Raten für den spontanen Zerfall sowie für den Zerfall durch Stöße zwischen zwei Dimeren oder zwischen einem Dimer und einem Atom.Ultracold quantum gases are ideal systems to experimentally tackle fundamental problems in both many- and few-body physics. The parameters characterizing such systems can be controlled and readout to an unprecedentedly high degree of precision. In this thesis, we discuss our experimental investigations of mixtures of two ultracold gases of different fermionic atom species, 6Li and 40K. The studies can be assigned to two main research themes. These are the fundamental many-body system consisting of an impurity in a Fermi sea on the one hand, and Li-K few-body physics on the other hand. To address the many-body physics of an impurity in a Fermi sea experimentally, we realize a mixture of a few K atoms and a large, dense cloud of fermionic Li atoms. The interaction between the impurity atoms and the atoms of the Fermi sea can be tuned by means of a magnetic Feshbach resonance. We then employ radio-frequency spectroscopy of the K atoms in various interaction regimes, ranging from strongly repulsive to strongly attractive, to reveal the energy landscape of the impurities in the Fermi sea. In the regime of strong interactions, where the scattering length exceeds the inter-particle separation, the impurity together with the excitation of the Fermi sea are described as a quasiparticle termed polaron, following Fermi liquid theory. We determine the energy, the residue, and the lifetime of such polarons in our system. Then, by applying a spin-echo technique, we investigate the decoherence of impurities in a Fermi sea as a function of the interaction strength. For moderate interaction strengths, our measurements provide a determination of the quasiparticle scattering rate. For near-resonant interactions, the decoherence rates are almost an order of magnitude larger. In another series of experiments, we probe the response of a Fermi sea to a rapidly introduced impurity on timescales much shorter than the Fermi time. Employing a Ramsey-type interferometry technique, we track the formation dynamics of repulsive and attractive polaron in real time. For resonant interactions, we observe the quantum interference arising from the simultaneous excitation of the corresponding repulsive and attractive many-body branches. To investigate the physics of Li-K few-body systems, we create dense samples of Li-K dimers from almost balanced mixtures of Li and K atoms. We then perform radio-frequency spectroscopy to investigate the elastic interactions of heavy K atoms with light-heavy Li-K dimers. Contrary to the atom-dimer interactions in a mass-balanced Fermi-Fermi mixture, our measurements reveal a strong K-LiK attraction in a regime of Li-K repulsion. This atom-dimer attraction is speculated to facilitate the access to the realization of exotic many-body states and phases. Whether it is possible to experimentally realize such phases, strongly depends on the lifetime of the atom-dimer mixture, which is typically limited by the lifetime of the dimer cloud. Therefore, we also investigate the lifetimes of dimer clouds as a function of the magnetic detuning from a Feshbach resonance. Our measurements allow us to discriminate between different contributions to the decay of our dimer sample and to determine accurate rates for the spontaneous decay as well as for the decay arising from collisions between two dimers or between one dimer and one atom.by Dipl.-Phys. Michael JagZusammenfassung in deutscher SpracheKumulative Dissertation aus fünf ArtikelnIm Titel ist 6 und 40 jeweils hochgestellt.Universität Innsbruck, Dissertation, 2016OeBB(VLID)138848