Cavity optomagnonics with magnetic textures: coupling a magnetic vortex to light

Optomagnonic systems, where light couples coherently to collective excitations in magnetically ordered solids, are currently of high interest due to their potential for quantum information processing platforms at the nanoscale. Efforts so far, both at the experimental and theoretical level, have focused on systems with a homogeneous magnetic background. A unique feature in optomagnonics is however the possibility of coupling light to spin excitations on top of magnetic textures. We propose a cavity-optomagnonic system with a non homogeneous magnetic ground state, namely a vortex in a magnetic microdisk. In particular we study the coupling between optical whispering gallery modes to magnon modes localized at the vortex. We show that the optomagnonic coupling has a rich spatial structure and that it can be tuned by an externally applied magnetic field. Our results predict cooperativities at maximum photon density of the order of $\mathcal{C}\approx10^{-2}$ by proper engineering of these structures.Comment: 16 pages, 11 figures, published versio

Stochastic Yield Catastrophes and Robustness in Self-Assembly

A guiding principle in self-assembly is that, for high production yield, nucleation of structures must be significantly slower than their growth. However, details of the mechanism that impedes nucleation are broadly considered irrelevant. Here, we analyze self-assembly into finite-sized target structures employing mathematical modeling. We investigate two key scenarios to delay nucleation: (i) by introducing a slow activation step for the assembling constituents and, (ii) by decreasing the dimerization rate. These scenarios have widely different characteristics. While the dimerization scenario exhibits robust behavior, the activation scenario is highly sensitive to demographic fluctuations. These demographic fluctuations ultimately disfavor growth compared to nucleation and can suppress yield completely. The occurrence of this stochastic yield catastrophe does not depend on model details but is generic as soon as number fluctuations between constituents are taken into account. On a broader perspective, our results reveal that stochasticity is an important limiting factor for self-assembly and that the specific implementation of the nucleation process plays a significant role in determining the yield

Trial and Error

Als Edward III. im Jahre 1337 einen Krieg mit Frankreich begann, war er aus strategischen Gründen dazu gezwungen, eine Allianz mit dem Kaiser des Heiligen Römischen Reiches und mehreren deutschen Fürsten einzugehen. Deshalb war es nötig hohe Summen an Bestechungsgeld an diese Verbündeten zu bezahlen. Kampfhandlungen sowie Diplomatie an anderen Fronten kosteten ebenfalls sehr viel Geld. Um diese Summen aufzubringen, griff der englische König auf verschiedenste Finanzierungspläne zurück. Direkte Steuern waren die einfachste Methode, allerdings erforderten sie die Zustimmung des Parlaments. In dem untersuchten Zeitraum war Edward III deshalb sehr um ihr Wohlwollen bemüht und musste häufig politische Zugeständnisse an das Unterhaus machen. Er fand aber bald heraus, dass er diese Zugeständnisse später widerrufen konnte, ohne mit ernsten Konsequenzen rechnen zu müssen. Der etwas schwierigere Weg der Finanzierung waren Kredite. Diese konnte er nur bekommen, da England damals der wichtigste Wollexporteur Europas war und vor allem die Tuchindustrie Flanderns vollkommen abhängig von englischer Wolle war. Mehrere Arten der Manipulation des Wollhandels wurden versucht, wobei vor allem die englischen Wollhändler und allen voran William de la Pole eine wichtige Rolle spielten. Anfängliche Versuche scheiterten aber ab 1343 wurde ein Finanzierungssystem verwendet das funktionierte. Das Jahr 1340 sah einen Bankrott des englischen Königs, da dieser die Ressourcen Englands überschätzt und sich durch militärische Abenteuer in Frankreich finanziell übernommen hatte. Gleichzeitig standen Teile seines Königreiches durch die hohe Steuerbelastung kurz vor einer Revolte. Edward provozierte daraufhin eine konstitutionelle Krise, die er dazu nutzte, viele einflussreiche politische Posten mit ihm bedingungslos loyalen Untergebenen neu zu besetzen. Aus dieser Krise ging er, aufgrund eines hohen Maßes an Pragmatismus und Opportunismus, hervor ohne etwas von seine

The consolidation trend in the luxury watch retail industry : taking the Bucherer Group as an example

2018 saw several large acquisitions in the luxury watch retail industry. For example, the Swiss family-owned Bucherer group acquired the American watch retail chain Tourneau and the Richemont group acquired the UK-based player Watchfinder. The question thus arises as to what prompted these recent large acquisitions in the luxury watch retail industry and what the underlying factors and reasons for such big international expansions are. The main goal of this Master’s thesis was to provide an answer to the yet uninvestigated question of why luxury watch retailers have increasingly begun to consolidate and what the drivers for this recent trend are. A further objective of this study was to shed light on the dynamics of the luxury watch retail industry and to identify critical success factors for companies actively operating as retailers of luxury watches. The very recent case of Bucherer’s acquisition of Tourneau was taken as an example throughout this thesis

Dissecting Supervised Contrastive Learning

Minimizing cross-entropy over the softmax scores of a linear map composed with a high-capacity encoder is arguably the most popular choice for training neural networks on supervised learning tasks. However, recent works show that one can directly optimize the encoder instead, to obtain equally (or even more) discriminative representations via a supervised variant of a contrastive objective. In this work, we address the question whether there are fundamental differences in the sought-for representation geometry in the output space of the encoder at minimal loss. Specifically, we prove, under mild assumptions, that both losses attain their minimum once the representations of each class collapse to the vertices of a regular simplex, inscribed in a hypersphere. We provide empirical evidence that this configuration is attained in practice and that reaching a close-to-optimal state typically indicates good generalization performance. Yet, the two losses show remarkably different optimization behavior. The number of iterations required to perfectly fit to data scales superlinearly with the amount of randomly flipped labels for the supervised contrastive loss. This is in contrast to the approximately linear scaling previously reported for networks trained with cross-entropy.Comment: ICML 2021 camera ready versio

TALKING INSTITUTIONS IN THE SHARING ECONOMY: A CONTENT ANALYSIS OF ACTOR QUOTES IN THE PRINT MEDIA AND A TAXONOMY OF DISCURSIVE STRATEGIES

We study how actors engage in institutional work to manage legitimacy by influencing media discourse in the face of discontinuous innovation. We content-analyze actor quotes reproduced in newspaper articles about the ‘sharing economy’ in the taxi and lodging industries to survey this aspect of media discourse and offer a taxonomy of the discursive strategies used in the public debate on institutional change. We find that actor quotes are dominantly from offensive actors striving for institutional change, mostly due to a relatively low share of voice of incumbent firms as defensive actors aiming at institutional maintenance. Whereas offensive actors aimed for legitimacy in their discursive strategies by balancing attacks on existing institutions with assertions of new institutions, defensive actors aimed for legitimacy more by attacking new institutions than by reinforcing existing ones. Our findings suggest that, contrary to prior beliefs, preventing the emergence of new institutions plays a crucial role for defensive institutional work

Information Systems for Sustainable Use of Water in Smart Cities: A Review and Call for Future Research

Water is the basis of life—that being said, the rising scarcity triggered by climate change and urbanization is an increasingly important challenge in urban areas. The United Nations present “water” as one of 17 Sustainable Development Goals (SDGs), and experts make impassionate calls for sustainable water management solutions as a seminal part of smart cities. While there are numerous research efforts in the IS community regarding certain SDGs and smart cities, we demonstrate in a structured literature review that urban water scarcity is still a blind spot. In this paper, we present pathways for future research alleys on this topic. We sketch out a vision for a smart city water system that is based on a novel information system. We draw on the energy informatics framework as a theoretical basis for our work and provide a context-specific discussion on its transferability to the resource of water in smart cities. By introducing urban water scarcity to the IS research agenda and showing opportunities as well as boundaries for the transfer of the energy informatics framework, we hope to stimulate IS researchers to be more active in pursuing research efforts in this pressing topic

Hip sonography update. Quality-management, catastrophes -tips and tricks

Abstract Aim: Hip sonography is today considered to be the diagnostic standard tool for developmental dysplasia of the hip (DDH) diagnosis. In Germany special commissions control the quality of the sonograms according to checklists to keep the standard high and to avoid over-and under -treatment. This paper lists tips and tricks to avoid typical mistakes according to these results. Material and method: In 8 German countries the quality of sonograms used to diagnose DDH was checked according to special checklists. An additional 250 medical doctors (pediatricians, radiologists, orthopaedic surgeons) were asked to classify 4 sonograms by measuring and typing. From the same group the projection (standing left, standing right, horizontal-cranial left, horizontal-cranial right) was checked according to the correct diagnosis in the shortest time. Results: In 1.6 % -43.7% the licence for hip sonography was withdrawn by the German commission. The best projection with the lowest rate of wrong interpretation was the "standing right"-projection. Most of the mistakes were made because of a wrong anatomical identification and usability check. Conclusion: Hip sonography must be trained by authorized teachers. The quality of the sonograms must be controlled according to checklists. The bedside teaching without control leads to a systematic teaching of mistakes and finally catastrophes