Magnetoresistance Induced by Rare Strong Scatterers in a High Mobility 2DEG

We observe a strong negative magnetoresistance at non-quantizing magnetic fields in a high-mobility two-dimensional electron gas (2DEG). This strong negative magnetoresistance consists of a narrow peak around zero magnetic field and a huge magnetoresistance at larger fields. The peak shows parabolic magnetic field dependence and is attributed to the interplay of smooth disorder and rare strong scatterers. We identify the rare strong scatterers as macroscopic defects in the material and determine their density from the peak curvature.Comment: 5 pages, 4 figure

Interlayer configurations of self-assembled folded graphene

The relative orientation between atomic lattices in twisted bilayer graphene opens up a whole new field of rich physics. So, the study of self-assembled twisted bilayer graphene gives deep insight into its underlying growth process. Cuts in monolayer graphene via the atomic force microscopy technique are used to start self-assembly and to generate a folding process. The final configurations for this self-assembly process are investigated. Here, the focus is on structures that arise from one cut. During the self-assembly, these structures not only move forward but also rotate. As it turns out, the final positions for all studied structures can be assigned to commensurate interlayer configurations

Magnetoresistance in a High Mobility Two-Dimensional Electron System as a Function of Sample Geometry

In a high mobility two-dimensional electron gas (2DEG) realized in a GaAs/Al0.3Ga0.7As quantum well we observe changes in the Shubnikov-de Haas oscillations (SdHO) and in the Hall resistance for different sample geometries. We observe for each sample geometry a strong negative magnetoresistance around zero magnetic field which consists of a peak around zero magnetic field and of a huge magnetoresistance at larger fields. The peak around zero magnetic field is left unchanged for different geometries

The role of thermodiffusion and dimensionality in the formation of cellular instabilities in hydrogen flames

Hydrogen is quickly becoming one of the most important fuels for combustion applications. However, compared to conventional hydro-carbon flames, the high diffusivity of hydrogen makes lean hydrogen flames prone to form cellular instabilities. In this work, the formation of cellular structures on a lean hydrogen–air flame is studied numerically in a laminar flow with prescribed initial perturbation. The flame is fully resolved and a detailed reaction mechanism as well as detailed diffusion models are utilized. In the literature, most numerical works directly studying cell formation are limited to two-dimensional setups. However, the additional principal curvature direction in three dimensions can have a strong impact on the cell formation and flame propagation. Because of this, simulations are performed both in 2D and 3D to directly quantify the effect of dimensionality on flame propagation. In the 3D simulations, higher local curvatures yield local heat release rates that exceed the ones from 2D simulations by 80%. In addition, simulations with and without thermo or Soret diffusion are carried out. While Soret diffusion leads to a decrease in flame speed for freely propagating flames, it accelerates the formation of thermodiffusively unstable cells as well as increases local heat release rates. This can be explained by an increase of local equivalence ratios in the reaction and post-oxidation zone due to the altered focusing of diffusive fluxes, leading to locally increased heat release rates for positively curved flame segments. The efficiency factor is evaluated to model the effect of the cellular structures on the local burning rate. increases during the formation of primary cells and reaches a quasi-steady value once the secondary structures are formed, which can present an approach for modeling the effect of cellular structures on hydrogen flame dynamics

Improved Source/Absorber Preparation for Radionuclide Spectrometry Based on Low-Temperature Calorimetric Detectors

High-resolution beta spectrometry based on low-temperature calorimetric detectors requires high-quality source/absorber combinations in order to avoid spectrum artifacts and to achieve optimal detection efficiency. In this work, preparation techniques and quality control methods to fabricate reliable source/absorber assemblies with the radionuclide under investigation embedded into them are discussed. © 2019, The Author(s)