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de Dijn, Annelien (2020): Freedom. An Unruly History: Cambridge/London: Harvard University Press. 426 Seiten. 31,50 €
No full textAnnelien de Dijns umfassenden Darstellung der Veränderung der westlichen Freiheitsvorstellung, die mehr als zwei Jahrtausende Ideengeschichte umfasst, und neben bekannten Theoretiker*innen auch politische Bewegungen und Parteiverständnisse referiert, verfolgt zwei Erzählstränge, die sich letztendlich auf die gängige Unterscheidung von positiver und negativer Freiheit beziehen, wie sie Benjamin Constant, Alexis de Tocqueville, Francis Lieber, Édouard René Lefebvre de Laboulaye, Johann Caspar Bluntschli und nicht zuletzt Isaiah Berlin als theoretische Differenzierung eingeführt haben. Laut Autorin wurde das ursprüngliche (westliche) Verständnis von Freiheit im alten Griechenland geboren und fiel dort zusammen mit der Rechtfertigung der Volksregierung oder Herrschaft des Volkes. Freiheit bedeutete die Abwesenheit von Fremdherrschaft und wurde mit Selbstregierung bzw. der Fähigkeit des Volkes, Kontrolle über die Art und Weise auszuüben, wie es regiert wurde, gleichgesetzt. Freiheit, in diesem positiven Sinne, bestimmte das Handeln der Athener Demokraten, römischen Plebejer, Florentiner Humanisten und amerikanischer Revolutionäre in ihrem Kampf gegen die bestehenden Machtstrukturen. Ihre Sprache der Freiheit war, wie die Autorin zeigt, überall dort anschlussfähig, wo soziale Gruppen und Bevölkerungen von der Politik weitgehend ausgeschlossen waren und für eine Öffnung von Staat und Verwaltung kämpften
Thermally activated dislocation mechanism in Mo studied by indentation, compression and impact testing
No full textBody-centered cubic metals like molybdenum and tungsten are interesting structural materials for high-temperature applications. These metals, are however, brittle at low homologous temperature, caused by the limited mobility of screw dislocations. In this study, the thermally activated deformation mechanisms in bcc Mo have been investigated using strain rate jump nanoindentation and compression tests as well as Charpy V-notch impact testing. The material shows a significant softening with increasing temperature and a maximum in strain rate sensitivity is found at the critical temperature, before decreasing again in the ductile regime. The activation volume, however, showed a distinct increase from about 5 b³ at the onset of the brittle to ductile transition temperature. Here we propose to use temperature-dependent nanoindentation strain rate jump testing and the activation volume as a complementary approach to provide some indication of the brittle to ductile transition temperature of bcc metals
Multiple phenotypic traits as triggers of host attacks towards ant symbionts: body size, morphological gestalt, and chemical mimicry accuracy
No full textBackground: Ant colonies are plagued by a diversity of arthropod guests, which adopt various strategies to avoid or to withstand host attacks. Chemical mimicry of host recognition cues is, for example, a common integration strategy of ant guests. The morphological gestalt and body size of ant guests have long been argued to also affect host hostility, but quantitative studies testing these predictions are largely missing. We here evaluated three guest traits as triggers of host aggression—body size, morphological gestalt, and accuracy in chemical mimicry—in a community of six Eciton army ant species and 29 guest species. We quantified ant aggression towards 314 guests in behavioral assays and, for the same individuals, determined their body size and their accuracy in mimicking ant cuticular hydrocarbon (CHC) profiles. We classified guests into the following gestalts: protective, myrmecoid, staphylinid-like, phorid-like, and larval-shaped. We expected that (1) guests with lower CHC mimicry accuracy are more frequently attacked; (2) larger guests are more frequently attacked; (3) guests of different morphological gestalt receive differing host aggression levels.
Results: Army ant species had distinct CHC profiles and accuracy of mimicking these profiles was variable among guests, with many species showing high mimicry accuracy. Unexpectedly, we did not find a clear relationship between chemical host similarity and host aggression, suggesting that other symbiont traits need to be considered. We detected a relationship between the guests’ body size and the received host aggression, in that diminutive forms were rarely attacked. Our data also indicated that morphological gestalt might be a valuable predictor of host aggression. While most ant-guest encounters remained peaceful, host behavior still differed towards guests in that ant aggression was primarily directed towards those guests possessing a protective or a staphylinid-like gestalt.
Conclusion: We demonstrate that CHC mimicry accuracy does not necessarily predict host aggression towards ant symbionts. Exploitation mechanisms are diverse, and we conclude that, besides chemical mimicry, other factors such as the guests’ morphological gestalt and especially their body size might be important, yet underrated traits shaping the level of host hostility against social insect symbionts
The Injectivity Radius of Souls of Alexandrov Spaces
No full textA sharp lower bound for the injectivity radius in noncompact nonnegatively curved Riemannian manifolds involving their soul goes back to Šarafutdinov. We generalize this bound to the setting of Alexandrov spaces. Our main theorem reads as follows. If the injectivity radius of an Alexandrov space of nonnegative curvature does not coincide with the one of its souls, then it is at least πK⁻¹/², where K is an upper curvature bound. We introduce the soul of Alexandrov spaces in some detail and compare two notions of injectivity radii
Piezoelectret metamaterials with a double-V structure exhibiting tunable piezoelectric effect in a broad range
No full textPiezoelectret metamaterials are a kind of piezoelectrets with distinctive properties such as negative Poisson's ratio and positive piezoelectric d₃₁ coefficient. These materials hold significant promise for applications in sensing and mechanical energy harvesting. In this article, flexible piezoelectret metamaterials with a simple double-V cell structure are designed, and their properties are theoretically analyzed, simulated, and experimentally tested. The results indicate that the effective piezoelectric d₃₃ and d₃₁ coefficients can be tuned over a wide range by adjusting the geometric parameters of the cell. The experimental results are consistent with the theoretical prediction and simulation calculation. Differing from the piezoelectric d₃₃ coefficient, which always has positive polarity, the sign of the piezoelectric d₃₁ coefficient depends on Poisson's ratio of the material. In particular, d₃₁ coefficients are negative for the materials with positive Poisson's ratio, while they have a positive sign when Poisson's ratio is negative. For a piezoelectret metamaterial sample prepared in this study, a large effective piezoelectric d₃₁ coefficient up to 1200 pC/N is achieved experimentally. The significant piezoelectric effects in the piezoelectret metamaterials as well as their excellent mechanical adaptivity to irregular surface structures, such as the curved surfaces of humanoid robots and aircraft wings, introduce a novel solution for diverse applications
A method for approximating high frequency sound radiation—The plane projection Rayleigh integral
No full textThe sound radiation of vibrating surfaces can be calculated using integral-based numerical methods. Due to the increasing discretization requirements, the computational effort increases significantly with increasing frequencies. Therefore, approximation methods with less computational effort are desirable. This paper introduces a method called the plane projection Rayleigh integral (PPRI), which combines low computational effort with high precision. The method approximates the sound radiation by applying the Rayleigh integral to a vibrating virtual plane representing the object in two dimensions. The method's performance is evaluated by comparing it to the visible element Rayleigh integral and the high frequency boundary element method (HFBEM), focusing on the accuracy and its dependence on radius of surface curvature, sound frequency, and distance from the surface. Analytical solutions for the breathing and oscillating sphere are used as benchmarks. The PPRI demonstrates the highest accuracy among the methods tested. Error values decrease significantly with larger radii and higher frequencies, falling below a 1% threshold at 4 times smaller Helmholtz numbers (radius-wavelength ratio) than the HFBEM. Additionally, the PPRI requires the least computational time in this consideration. Thus, the PPRI achieves both high precision and efficiency
Suppressing Bifurcation in Bolt-Clamped Langevin Ultrasonic Transducers Through AC Current-Driven Control
No full textBolt-clamped Langevin ultrasonic transducers are
widely used in industrial, medical, and research applications
attributed to their ability to generate high-power ultrasonic
waves. Due to their large quality factor, it is important to
hit the exact resonance frequency to achieve their maximum
performance. Voltage-controlled excitation of these transducers
often leads to bifurcation, a scenario where multiple valid phase
angles result in varied power outputs at the resonance frequency.
In this work, we model the nonlinearities that occur within the
transducer via an extended Butterworth Van Dyke (BVD) model
and use it to explain why an AC current-driven control suppresses
the bifurcation. This involves modelling the damping behavior,
which is subsequently verified through surface velocity measurements
using a laser Doppler vibrometer. We propose a circuit
that facilitates current-controlled AC voltage output, detailing
its components and evaluating its impact on the transducer’s
dynamics. Our method prevents impedance curve jumps and
improves the transducer’s transient rise time from 12.7 ms to
0.9 ms and reduces the fall time from 6.9 ms to 1.2 ms, offering
a fast and robust solution. Despite the increased complexity
of the current-controlled circuitry, our findings demonstrate its
efficacy in maintaining consistent performance near the resonant
frequency, thus, opening new avenues for improving bolt-clamped
Langevin ultrasonic transducers in applications such as acoustic
levitation or ultrasonic cleaning
Aryl Radicals Generated from Aryl Pinacol Boronates Modify Peptides and Proteins
No full textWe report here a distinct reaction, which generates aryl radicals from aryl pinacol boronates under mild aqueous conditions and can be used for peptide and protein modifications. The strategy leverages the versatile reactivity of aryl pinacol boronates to form aryl radicals in presence of ammonium persulfate (APS). The formed aryl radicals insert readily into peptide disulfide bonds while tolerating other functionalities. On the protein level, the reactivity extends beyond the disulfide bonds. The methodology benefits from the accessibility of starting aryl pinacol boronates, as well as biocompatible conditions. In contrast to conventional methods used for aryl radical generation, the strategy is metal‐free, does not require photoinduction and can be readily performed under aqueous conditions. The mechanism of the reactions was investigated by radical‐trapping experiments, spectroscopic analysis and oxygen scavenging. The presented approach broadens the application of aryl pinacol boronate esters in radical reactions
The influence of ionic liquid modification on the restructuring of trimetallic PtNiMo/C catalysts during conditioning
No full textDuring preconditioning of PtNiMo/C catalyst metal dissolution and redeposition takes place. At slow scan rates this leads to increased steady activity for oxygen reduction reaction (ORR). Furthermore, ionic liquids (IL) influence the activity of Pt‐based catalysts and can alter the leaching of Pt‐alloy catalysts. This study investigates the influence of ILs on the preconditioning of PtNiMo/C catalysts. Therefore, preconditioning parameters as well as the IL employed were varied. ILs with long side chains like [C8fC1][BETI] resulted in a spreading of the activity development during preconditioning over a longer cycle time and with damped amplitude for the activity changes. For shorter side chains like [BMIM][BETI] the development is like the pristine catalyst. Ex‐situ and in‐situ characterization revealed that [BMIM][BETI] leached fast to the electrolyte, which was not observed for the other ILs. Nevertheless, for all ILs a strongly reduced platinum leaching was observed. Even for the leached [BMIM][BETI] a stable wetting layer influencing the leaching seems to remain. Nevertheless, only for the other ILs where an immobilized bulk phase is remaining a difference in catalyst restructuring during the preconditioning is observed and a higher number of small sized Pt clusters and a lower amount of bigger Pt clusters resulted
Effizienzsteigerung des Hybrid-Antriebsstrangs durch Integration einer prädiktiven online-optimierenden Betriebsstrategie
No full textHybridfahrzeuge werden künftig eine zunehmend wichtige Rolle spielen, da sie erhebliches Potenzial zur Reduktion von Kraftstoffverbrauch und Emissionen bieten. Dieses Potenzial ergibt sich aus der Möglichkeit, die Leistungsanforderungen auf mehrere Energiewandler zu verteilen, wobei die optimale Auswahl der Betriebszustände eine zentrale Herausforderung darstellt. Aufgrund der Notwendigkeit, die Nutzung von fossilen Energieträgern so gut es geht zu reduzieren, um dem Klimawandel vorzubeugen, ist die bestmögliche Nutzung dieses Potenzials daher von großem Wert.
In Rahmen der vorliegenden Arbeit wird eine Entwicklungsumgebung aufgebaut, um das Potenzial einer prädiktiven Betriebsstrategie zu untersuchen. Diese Strategie schätzt die zukünftigen Leistungsanforderungen anhand eines definierten Prädiktionshorizonts ab und optimiert die Drehmomentverteilung zwischen Verbrennungs- und Elektromotor. In einer Co-Simulationsumgebung wird ein Gesamtfahrzeugmodell aufgebaut und mit realen Messdaten validiert. Dies beinhaltet die Ableitung von Fahrzeugparametern und die Erstellung eines Fahrermodells, um unterschiedliche Fahrszenarien zu simulieren. Das Modell wird durch Simulationen getestet, bei denen das virtuelle Modell mit realer Hardware verglichen wird. Für die prädiktive Strategie wird ein Optimierer entwickelt, der die Effizienz von Elektro- und Verbrennungsmotor anhand einer Kostenfunktion bewertet. Hierbei wird der Äquivalenzfaktor dynamisch an die prädizierten Lastanforderungen angepasst, was eine prädiktive Entscheidungsfindung ermöglicht. Bei der Datenakquise für die Prädiktionsberechnung werden Fahrzeug- und Fahrerdaten aus Messungen sowie Routeninformationen aus Cloud-Services verwendet. Ein speziell entwickeltes Modul ruft Geodaten ab und integriert sie in die Co-Simulationsumgebung, um Prädiktionsvektoren für die prädiktive Strategie zu erstellen. Zur Implementierung und Validierung werden die Modelle in der Co-Simulationsumgebung zusammengeführt. Weitere Simulationen dienen der Kalibrierung der prädiktiven Strategie und der Bewertung ihres Einflusses auf Energieeinsparung und Fahrkomfort.
Die Simulationen zeigen eine mögliche Kraftstoffreduktion von etwa 14 % bei perfekter Geschwindigkeitsprädiktion und bis zu 12 % bei berechneten Prädiktionen. Insgesamt bestätigten die Ergebnisse die Robustheit der prädiktiven Strategie, auch bei leichten Abweichungen oder Messstörungen