Superradiant Emission from Coherent Excitons in van Der Waals Heterostructures

Recent advancements in isolation and stacking of layered van der Waals materials have created an unprecedented paradigm for demonstrating varieties of 2D quantum materials. Rationally designed van der Waals heterostructures composed of monolayer transition-metal dichalcogenides (TMDs) and few-layer hBN show several unique optoelectronic features driven by correlations. However, entangled superradiant excitonic species in such systems have not been observed before. In this report, it is demonstrated that strong suppression of phonon population at low temperature results in a formation of a coherent excitonic-dipoles ensemble in the heterostructure, and the collective oscillation of those dipoles stimulates a robust phase synchronized ultra-narrow band superradiant emission even at extremely low pumping intensity. Such emitters are in high demand for a multitude of applications, including fundamental research on many-body correlations and other state-of-the-art technologies. This timely demonstration paves the way for further exploration of ultralow-threshold quantum-emitting devices with unmatched design freedom and spectral tunability.     

Flexible,Mechanically Stable,Porous Self-Standing Microfiber Network Membranes of Covalent Organic Frameworks: Preparation Method and Characterization

Covalent organic frameworks (COFs) show advantageous characteristics, such as an ordered pore structure and a large surface area for gas storage and separation, energy storage, catalysis, and molecular separation. However, COFs usually exist as difficult-to-process powders, and preparing continuous, robust, flexible, foldable, and rollable COF membranes is still a challenge. Herein, such COF membranes with fiber morphology for the first time prepared via a newly introduced template-assisted framework process are reported. This method uses electrospun porous polymer membranes as a sacrificial large dimension template for making self-standing COF membranes. The porous COF fiber membranes, besides having high crystallinity, also show a large surface area (1153 m² g⁻¹), good mechanical stability, excellent thermal stability, and flexibility. This study opens up the possibility of preparation of large dimension COF membranes and their derivatives in a simple way and hence shows promise in technical applications in separation, catalysis, and energy in the future.     

Analyse von Lkw-Überholmanövern auf Autobahnen für die Entwicklung kooperativer Fahrerassistenzsysteme

Forschung im Ingenieurwesen - Lkw-Überholmanöver auf Autobahnen können Konfliktsituationen provozieren. Das lange Blockieren der Überholspur und plötzliche Ausscheren kann...     

High yield formation of carbon nanotubes using a rotating cathode in open air

Carbon nanotubes (CNTs) have been synthesized using the arc discharge method with a rotating graphite disc as the cathode. Arcing was carried out in open air and without the use of catalysts. The current density was maintained constant through out the experiment, while, the rate of rotation of the cathode and atmosphere under which arcing was carried out were changed during experimentation. Characterization of the samples produced indicates that rotation of the cathode has a significant impact on the quality and yield of the process. It is proposed that rotation of the cathode drags plasma formed between two electrodes away from high temperature region. This results in a sudden quenching of the reactive plasma. The time available for nucleation and growth phenomena is significantly reduced and thus leads to the formation of highly graphitic multi walled CNTs (yield 60%) and traces of double walled CNTs.     

Pretreatment of Highly Polluted Pharmaceutical Waste Broth by Wet Air Oxidation

The preoxidation of a highly polluted waste pharmaceutical fermentation broth using wet air oxidation (WAO) has been studied as a possible method for the effective removal of organics. The applied (pre)treatment method should enhance the biotreatability of the pharmaceutical fermentation broth in terms of reduced initial toxicity and higher biodegradability. Preliminary experiments in the pilot biological treatment plant were successful only at low organic loads, whereas the system collapses at higher ones. The characterization of the fermentation broth was started by common physicochemical analysis, whereas several bioassays were used to determine its impact on biological treatment plants and the environment. Toxicity prior to and after WAO was determined using the acute Vibrio fischeri test, measurement of inhibition of O2 consumption, and the Daphnia magna acute test. Ready biodegradability of the treated and untreated broth has also been assessed. WAO experiments were accomplished in the 2?L batch reactor at different temperatures (240/280°C) and operating pressures. WAO experiments confirmed reduction of the toxicity toward microorganisms, whereas oxidized wastewater was more toxic to daphnids. Biodegradability of the oxidized broth has also been enhanced. Further work has been focused on designing appropriate combination of WAO and biological processes.     

From particle-mass to multibody systems: graph-theoretic modeling

The distinction between geometry and dynamic interactions is fundamental for the consistent dynamic analysis of physical systems. A unified treatment of such systems is possible when we adopt a hierarchical mathematical model with a consistent set of embedded abstractions. This new view is adopted in the general formulation strategy for obtaining a simplified dynamics model of mechanical systems. We show that there exists a consistent general extension from the model of constrained particle-mass systems (PMS) to the model of multibody systems (MBS) based entirely on graph-theoretic concepts