Experiments on transformation thermodynamics: Molding the flow of heat

It has recently been shown theoretically that the time-dependent heat conduction equation is form-invariant under curvilinear coordinate transformations. Thus, in analogy to transformation optics, fictitious transformed space can be mapped onto (meta-)materials with spatially inhomogeneous and anisotropic heat-conductivity tensors in the laboratory space. On this basis, we design, fabricate, and characterize a micro-structured thermal cloak that molds the flow of heat around an object in a metal plate. This allows for transient protection of the object from heating, while maintaining the same downstream heat flow as without object and cloak.Comment: 10 pages, 4 figure

Hall-effect sign-inversion in a realizable 3D metamaterial

In 2009, Briane and Milton proved mathematically the existence of three-dimensional isotropic metamaterials with a classical Hall coefficient which is negative with respect to that of all of the metamaterial constituents. Here, we significantly simplify their blueprint towards an architecture composed of only a single constituent material in vacuum/air, which can be seen as a special type of porosity. We show that the sign of the Hall voltage is determined by a separation parameter between adjacent tori. This qualitative behavior is robust even for only a small number of metamaterial unit cells. The combination of simplification and robustness brings experimental verifications of this striking sign-inversion into reach.Comment: 9 figures, 7 page

On three-dimensional dilational elastic metamaterials

Dilational materials are stable three-dimensional isotropic auxetics with an ultimate Poisson's ratio of -1. We design, evaluate, fabricate, and characterize crystalline metamaterials approaching this ideal. To reveal all modes, we calculate the phonon band structures. On this basis, using cubic symmetry, we can unambiguously retrieve all different non-zero elements of the rank-4 effective metamaterial elasticity tensor, from which all effective elastic metamaterial properties follow. While the elastic properties and the phase velocity remain anisotropic, the effective Poisson's ratio indeed becomes isotropic and approaches -1 in the limit of small internal connections. This finding is also supported by independent static continuum-mechanics calculations. In static experiments on macroscopic polymer structures fabricated by three-dimensional printing, we measure Poisson's ratios as low as -0.8 in good agreement with theory. Microscopic samples are also presented.Comment: 8 figure

Phonon band structures of three-dimensional pentamode metamaterials

Three-dimensional pentamode metamaterials are artificial solids that approximately behave like liquids, which have vanishing shear modulus. Pentamodes have recently become experimental reality. Here, we calculate their phonon band structures for various parameters. Consistent with static continuum mechanics, we find that compression and shear waves exhibit phase velocities that can realistically be different by more than one order of magnitude. Interestingly, we also find frequency intervals with more than two octaves bandwidth in which pure single-mode behavior is obtained. Herein, exclusively compression waves exist due to a complete three-dimensional band gap for shear waves and, hence, no coupling to shear modes is possible. Such single-mode behavior might, e.g., be interesting for transformation-elastodynamics architectures.Comment: 5 figure

Bedeutsame Momente im Coaching

Auf der Grundlage einer differenzierten Kritik an der aktuellen Coaching-Forschung wird in diesem Open-Access-Buch eine Landkarte für die künftige Ausrichtung der Coaching-Prozessforschung vorgestellt. Als weiteres Ergebnis seiner Arbeit stellt Robert Wegener ein methodisches Verfahren zur Untersuchung «bedeutsamer Momente» vor. Ziel des Verfahrens ist es, dem Gegenstand Coaching und insbesondere dessen dynamischem und komplexem Charakter in besonderer Weise Rechnung zu tragen. Ausgangspunkt dafür ist das theoretische Verständnis «bedeutsamer Momente» im Coaching, das Wegener mit einer eigenen Coaching-Definition und verschiedenen psychotherapiebezogenen Forschungsrichtungen herleitet und für die Entwicklung und Erprobung seines Forschungsdesigns konsequent verwendet. Dieses Buch bildet eine erste Grundlage für eine programmatisch angelegte Forschung über «bedeutsame Momente» im Coaching

Altus Galaxy: Readers' Preferences for Six Categories of News Stories

Questionable readership, the rise of military underground publications, and the end of the draft and dawn of the all-volunteer era prompted Air Force commanders, information officers and editors to question the values of their base newspapers in the early 1970s. During this period, I was editor of the Altus Galaxy, one of the Air Force's 150 base newspapers. As a "gatekeeper," I frequently was sweet-talked, cajoled, badgered, shoved and tugged by fellow Air Force members, and even their wives, "to get their story in the paper." Faced with deadlines, a limited staff and not enough editorial space, I often wondered what news was interesting and valuable to my audience, and what--barring directives from higher up--should receive top priority. This exploratory study was aimed at finding out readers' preferences for different types of news stories in the Altus Galaxy, Altus Air Force Base's newspaper.Mass Communicatio

Transfer of Reinforcement Learning-Based Controllers from Model- to Hardware-in-the-Loop

The process of developing control functions for embedded systems is resource-, time-, and data-intensive, often resulting in sub-optimal cost and solutions approaches. Reinforcement Learning (RL) has great potential for autonomously training agents to perform complex control tasks with minimal human intervention. Due to costly data generation and safety constraints, however, its application is mostly limited to purely simulated domains. To use RL effectively in embedded system function development, the generated agents must be able to handle real-world applications. In this context, this work focuses on accelerating the training process of RL agents by combining Transfer Learning (TL) and X-in-the-Loop (XiL) simulation. For the use case of transient exhaust gas re-circulation control for an internal combustion engine, use of a computationally cheap Model-in-the-Loop (MiL) simulation is made to select a suitable algorithm, fine-tune hyperparameters, and finally train candidate agents for the transfer. These pre-trained RL agents are then fine-tuned in a Hardware-in-the-Loop (HiL) system via TL. The transfer revealed the need for adjusting the reward parameters when advancing to real hardware. Further, the comparison between a purely HiL-trained and a transferred agent showed a reduction of training time by a factor of 5.9. The results emphasize the necessity to train RL agents with real hardware, and demonstrate that the maturity of the transferred policies affects both training time and performance, highlighting the strong synergies between TL and XiL simulation