String Gas Cosmology

We present a critical review and summary of String Gas Cosmology. We include a pedagogical derivation of the effective action starting from string theory, emphasizing the necessary approximations that must be invoked. Working in the effective theory, we demonstrate that at late-times it is not possible to stabilize the extra dimensions by a gas of massive string winding modes. We then consider additional string gases that contain so-called enhanced symmetry states. These string gases are very heavy initially, but drive the moduli to locations that minimize the energy and pressure of the gas. We consider both classical and quantum gas dynamics, where in the former the validity of the theory is questionable and some fine-tuning is required, but in the latter we find a consistent and promising stabilization mechanism that is valid at late-times. In addition, we find that string gases provide a framework to explore dark matter, presenting alternatives to $\Lambda$CDM as recently considered by Gubser and Peebles. We also discuss quantum trapping with string gases as a method for including dynamics on the string landscape.Comment: 55 pages, 1 figure, minor corrections, version to appear in Reviews of Modern Physic

A Terminal Velocity on the Landscape: Particle Production near Extra Species Loci in Higher Dimensions

We investigate particle production near extra species loci (ESL) in a higher dimensional field space and derive a speed limit in moduli space at weak coupling. This terminal velocity is set by the characteristic ESL-separation and the coupling of the extra degrees of freedom to the moduli, but it is independent of the moduli's potential if the dimensionality of the field space is considerably larger than the dimensionality of the loci, D >> d. Once the terminal velocity is approached, particles are produced at a plethora of nearby ESLs, preventing a further increase in speed via their backreaction. It is possible to drive inflation at the terminal velocity, providing a generalization of trapped inflation with attractive features: we find that more than sixty e-folds of inflation for sub-Planckian excursions in field space are possible if ESLs are ubiquitous, without fine tuning of initial conditions and less tuned potentials. We construct a simple, observationally viable model with a slightly red scalar power-spectrum and suppressed gravitational waves; we comment on the presence of additional observational signatures originating from IR-cascading and individual massive particles. We also show that moduli-trapping at an ESL is suppressed for D >> d, hindering dynamical selection of high-symmetry vacua on the landscape based on this mechanism.Comment: 46 pages, 6 figures. V3: typos corrected compared to JHEP version, conclusions unchange

Von Rotaxanen als potenziellen Enzym-Mimetika zu massenspektrometrischen Untersuchungen dendritischer Verbindungen in der hochverdünnten Gasphase

Im Rahmen dieser Arbeit konnte ein mehrfach-funktionalisiertes [2]Rotaxan synthetisiert werden, das sich möglicherweise als künstliches Enzym für die Polymerisationsreaktion von Aminosäurederivaten einsetzen lässt. Neben dem vollständig funktionalisierten Derivat wurden auch verschiedene andere Rotaxane hergestellt, die nicht über alle für die Katalyse notwendigen Einheiten im Molekülgerüst verfügen. Diese Rotaxane werden für zukünftige Vergleichsexperimente verwendet, um die katalytische Aktivität des vollständig funktionalisierten Derivats zu überprüfen. In einem weiteren Projekt wurde untersucht, ob auch einzelne Untereinheiten von Rotaxanen zur Beschleunigung von Reaktionen eingesetzt werden können. Durch die Zugabe von 5 mol% eines Tetralactam-Makrozyklus’ konnte eine Diels-Alder-Reaktion um 30% beschleunigt werden. Dieses Konzept wurde ebenfalls zur Rotaxansynthese verwendet, indem zwei Stoppereinheiten jeweils mit einem Dien und einem Dienophil versehen wurden. Der Amid-Templateffekt wurde für die Synthese einer Vielzahl von Rotaxanen eingesetzt. In dieser Arbeit wurde ebenfalls der Einfluss von Substituenten auf diesen Templateffekt untersucht. Hierzu wurden verschieden substituierte Amid-Gastmoleküle synthetisiert und in einem Tetralactam-Reif eingelagert. Die Bestimmung der Bindungskonstanten und Bindungsenergien erfolgte durch 1H-NMR-Titrationsexperimente. Hierbei zeigte sich, dass kein Effekt des Substituenten auf die Wirt/Gast-Wechselwirkung zu beobachten ist. Verschiedene Makrozyklen konnten im Rahmen dieser Arbeit synthetisiert werden. Von diesen Zyklen wurde bereits ein Tetralactam-Makrozyklus auf einer Au(111)-Oberfläche abgeschieden und mit der Rastertunnelmikroskopie untersucht. Der Reif bildet durch Selbstorganisation zwei unterschiedlich stabile Domänen (alpha- und beta-Phase) aus. Während die kinetisch stabilisierte beta-Phase aus trimeren Einheiten aus Makrozyklen besteht, bilden in der thermodynamisch stabilen alpha-Phase dimere Einheiten das zugrundeliegende Strukturelement. Mit der Massenspektrometrie wurden verschiedene an der Peripherie persulfonierte Dendrimere vom TREN-, POPAM- und Oligosulfonimid-Typ untersucht. Während die MALDI- Massenspektrometrie zu einem falsch-negativen Ergebnis über die Reinheit der untersuchten Proben führt, wird mit der ESI-Massenspektrometrie ein realistischeres Bild über die strukturelle Perfektion der Dendrimere erhalten. Die massenspektrometrischen Untersuchungen zeigten, dass beim MALDI-Prozess die gleichen Fragmente gebildet werden, die ebenfalls in einer unvollständigen Substitutionsreaktion bei der Dendrimer-Synthese entstehen können. Tandem-MS-Experimente stellten sich außerdem als ein wertvolles Hilfsmittel bei der Untersuchung und Unterscheidung verschiedener Dendrimer-Defektvarianten heraus.From Rotaxanes as Potential Enzyme Mimic to Mass Spectrometric Investigations of Dendritic Compounds in the Highly Diluted Gas Phase This work describes the synthesis of a multi-functionalized [2]rotaxane which could potentially be used as an artificial enzyme for the polymerization of amino acid derivatives. In addition to the fully functionalized rotaxane which contains all the necessary functional groups for catalysis, a series of partially functionalized rotaxanes was synthesized. The latter rotaxanes will be used in control experiments to demonstrate the catalytic activity of the fully functionalized rotaxane. Furthermore, the acceleration of reactions by rotaxane subunits was investigated, e.g. by the tetralactam macrocycle. With the addition of 5 mol% of the macrocycle, a Diels-Alder reaction was accelerated by 30%. This concept was also used for the synthesis of a rotaxane. Therefore two stoppers were functionalized with a diene and a dienophile group respectively. The amide template has been used for the synthesis of various rotaxanes. In this work the influence of substituents on the template effect was investigated in detail. Different amide guest molecules were synthesized and bound in the cavity of the tetralactam macrocycle. The binding constants and the corresponding energies were determined by 1H-NMR titration experiments. Interestingly, the results show no effect of the substituent on the host/guest interaction. One of the various macrocycles synthesized in this work was deposited on a Au(111) surface and examined by STM (scanning tunneling microscope). The wheel forms two different stable domains (referred to as the alpha- and beta-phase) on the surface. While the kinetically stabilized beta-phase consists of trimers of the wheel, the underlying structural motif in the thermodynamically stable alpha-phase is a dimeric unit. A series of TREN, POPAM and oligo sulfonimide dendrimers persulfonated at their periphery was investigated by mass spectrometry. While MALDI of the dendrimers leads to a false-negative result concerning the purity of the examined samples, ESI mass spectrometry shows a more realistic view on the structural perfection of these molecules. The detailed mass spectrometric analysis shows that in the MALDI process the same fragments are generated, which can also be the result of an incomplete substitution reaction in the synthesis. In addition, tandem MS experiments proved to be a valuable tool for the analysis and discrimination of different dendrimer defects

Alternation and tunable composition in hydrogen bonded supramolecular copolymers

Sequence control in supramolecular copolymers is limited by the selectivity of the associating monomer end groups. Here we introduce the use of monomers with aminopyrimidinone and aminohydroxynaphthyridine quadruple hydrogen bonding end groups, which both homodimerize, but form even stronger heterodimers. These features allow the formation of supramolecular copolymers with a tunable composition and a preference for alternating sequences

Disilane cleavage with selected alkali and alkaline earth metal salts

The industry‐scale production of methylchloromonosilanes in the Müller–Rochow Direct Process is accompanied by the formation of a residue, the direct process residue (DPR), comprised of disilanes MenSi2Cl6‐n (n=1–6). Great research efforts have been devoted to the recycling of these disilanes into monosilanes to allow reintroduction into the siloxane production chain. In this work, disilane cleavage by using alkali and alkaline earth metal salts is reported. The reaction with metal hydrides, in particular lithium hydride (LiH), leads to efficient reduction of chlorine containing disilanes but also induces disproportionation into mono‐ and oligosilanes. Alkali and alkaline earth chlorides, formed in the course of the reduction, specifically induce disproportionation of highly chlorinated disilanes, whereas highly methylated disilanes (n>3) remain unreacted. Nearly quantitative DPR conversion into monosilanes was achieved by using concentrated HCl/ether solutions in the presence of lithium chloride

Disilane Cleavage with Selected Alkali and Alkaline Earth Metal Salts

The industry‐scale production of methylchloromonosilanes in the Müller–Rochow Direct Process is accompanied by the formation of a residue, the direct process residue (DPR), comprised of disilanes MenSi2Cl6‐n (n=1–6). Great research efforts have been devoted to the recycling of these disilanes into monosilanes to allow reintroduction into the siloxane production chain. In this work, disilane cleavage by using alkali and alkaline earth metal salts is reported. The reaction with metal hydrides, in particular lithium hydride (LiH), leads to efficient reduction of chlorine containing disilanes but also induces disproportionation into mono‐ and oligosilanes. Alkali and alkaline earth chlorides, formed in the course of the reduction, specifically induce disproportionation of highly chlorinated disilanes, whereas highly methylated disilanes (n>3) remain unreacted. Nearly quantitative DPR conversion into monosilanes was achieved by using concentrated HCl/ether solutions in the presence of lithium chloride

Flexible long-range surface plasmon polariton single-mode waveguide for optical interconnects

International audienceWe present the design, fabrication and characterization of long-range surface plasmon polariton waveguide arrays with materials, mainly silicones, carefully selected with the aim to be used as mechanically flexible single-mode optical interconnections, the so-called “plasmonic arc” working at 1.55µm. The fabricated plasmonic arcs show a TM/TE polarization ratio of ~25 dB. By using the cut-back method, the straight propagation loss at 1.55µm is estimated to 0.5-1 dB/mm and coupling loss to ~1-2 dB/facet after dicing. In the free-standing S-curved configuration, the bending loss of single cladding plasmonic arc is 2.2-2.8 dB/90° at bending radius 2.5 mm. For double cladding plasmonic arcs, it is decreased to 0.7-1.7 dB/90° for the same radius. The coupling loss with single-mode glass PCB waveguides is estimated to be 1.7 dB/interface in the best condition

Money Illusion and the Double Dividend in the Short Run

In their seminal paper, Bovenberg and De Mooij (1994) elucidate why an ecological tax reform will not yield a double dividend, i.e. fails to increase the efficiency of the tax system. The present paper slightly modifies the Bovenberg and De Mooij model by introducing money illusion. With this modification, an environmental tax reform that raises the price level may generate a double dividend, since the additional tax on the dirty good does not reduce labor supply. A prerequisite for the double dividend to occur is a sufficiently small elasticity of substitution between clean and dirty consumption. Moreover, accounting for money illusion always reduces the intertemporal gross cost of the tax reform

The Rise and Fall of Festivals - Reflections on the Salzburg Festival

The paper takes a closer look at cultural festivals such as musical or operatic festivals. From an economic viewpoint the paper shows that such festivals offer great artistic and economic opportunities, but that at the same time these opportunities are also easy to destroy. Empirical evidence from the Salzburg Festival show that government support can have negative effects on the innovative and economically success of festivals by introducing distorting incentives and imposing all sorts of restrictions. The paper draws policy suggestions on how the state can support art festivals

Choosing the Joneses: On the Endogeneity of Reference Groups

"A growing economic literature recognizes and deals with the fact that economic agents' utility and well-being is not solely determined by absolute achievements, but also by achievements relative to a reference standard or reference group. In this literature it is assumed that the reference standard is completely exogenous. Social psychologists have questioned the exogenous nature of the comparison process (""forced comparison conception"") and have emphasized that people play a more active role in the determination of their reference standards (""coping approach""). The present paper takes up this idea. In our model the reference standard is determined endogenously. Following the social comparison literature we assume that in choosing the optimal reference standard people pursue goals of self-improvement and self-enhancement. Our model predicts that the optimally chosen reference standard (or group) increases in people's abilities. We present new questionnaire data together with a review of various important findings from social perception studies (minimum income, happiness, subjective social class). It turns out that the empirical regularities conform well to the predictions of our model, but are difficult (if not impossible) to explain by both the standard economic approach (with its neglect of social comparison) and the forced comparison approach.