Quantum Transport and Shot Noise in Graphene-Boron Nitride Heterostructures

This thesis presents experiments on the electronic transport properties of mesoscopic graphene samples at low temperature. Due to the residue free encapsulation in hexagonal boron nitride, the mean free path of charge carriers is in the order of the geometric sample dimensions. High frequency shot noise was measured in parallel to the conductance under various experimental conditions, including proximity induced superconductivity and high magnetic fields

Synaptotagmin-7 Is an Asynchronous Calcium Sensor for Synaptic Transmission in Neurons Expressing SNAP-23

Synchronization of neurotransmitter release with the presynaptic action potential is essential for maintaining fidelity of information transfer in the central nervous system. However, synchronous release is frequently accompanied by an asynchronous release component that builds up during repetitive stimulation, and can even play a dominant role in some synapses. Here, we show that substitution of SNAP-23 for SNAP-25 in mouse autaptic glutamatergic hippocampal neurons results in asynchronous release and a higher frequency of spontaneous release events (mEPSCs). Use of neurons from double-knock-out (SNAP-25, synaptotagmin-7) mice in combination with viral transduction showed that SNAP-23-driven release is triggered by endogenous synaptotagmin-7. In the absence of synaptotagmin-7 release became even more asynchronous, and the spontaneous release rate increased even more, indicating that synaptotagmin-7 acts to synchronize release and suppress spontaneous release. However, compared to synaptotagmin-1, synaptotagmin-7 is a both leaky and asynchronous calcium sensor. In the presence of SNAP-25, consequences of the elimination of synaptotagmin-7 were small or absent, indicating that the protein pairs SNAP-25/synaptotagmin-1 and SNAP-23/synaptotagmin-7 might act as mutually exclusive calcium sensors. Expression of fusion proteins between pHluorin (pH-sensitive GFP) and synaptotagmin-1 or -7 showed that vesicles that fuse using the SNAP-23/synaptotagmin-7 combination contained synaptotagmin-1, while synaptotagmin-7 barely displayed activity-dependent trafficking between vesicle and plasma membrane, implying that it acts as a plasma membrane calcium sensor. Overall, these findings support the idea of alternative syt∶SNARE combinations driving release with different kinetics and fidelity

Tailoring supercurrent confinement in graphene bilayer weak links

The Josephson effect is one of the most studied macroscopic quantum phenomena in condensed matter physics and has been an essential part of the quantum technologies development over the last decades. It is already used in many applications such as magnetometry, metrology, quantum computing, detectors or electronic refrigeration. However, developing devices in which the induced superconductivity can be monitored, both spatially and in its magnitude, remains a serious challenge. In this work, we have used local gates to control confinement, amplitude and density profile of the supercurrent induced in one-dimensional nanoscale constrictions, defined in bilayer graphene-hexagonal boron nitride van der Waals heterostructures. The combination of resistance gate maps, out-of-equilibrium transport, magnetic interferometry measurements, analytical and numerical modelling enables us to explore highly tunable superconducting weak links. Our study opens the path way to design more complex superconducting circuits based on this principle such as electronic interferometers or transition-edge sensors

Tuning Anti-Klein to Klein Tunneling in Bilayer Graphene

We show that in gapped bilayer graphene, quasiparticle tunneling and the corresponding Berry phase can be controlled such that they exhibit features of single-layer graphene such as Klein tunneling. The Berry phase is detected by a high-quality Fabry-Pérot interferometer based on bilayer graphene. By raising the Fermi energy of the charge carriers, we find that the Berry phase can be continuously tuned from 2π down to 0.68π in gapped bilayer graphene, in contrast to the constant Berry phase of 2π in pristine bilayer graphene. Particularly, we observe a Berry phase of π, the standard value for single-layer graphene. As the Berry phase decreases, the corresponding transmission probability of charge carriers at normal incidence clearly demonstrates a transition from anti-Klein tunneling to nearly perfect Klein tunneling

Penggambaran superhero pada tokoh Deadpool dalam film Deadpool

Deadpool merupakan film superhero yang diproduksi oleh Marvel Studio pada tahun 2016. Film ini menceritakan sosok superhero yang memiliki sisi lain dari superhero pada umumnya. Penelitian ini bertujuan untuk melihat bagaimana tanda-tanda penggambaran superhero pada tokoh Deadpool dalam film Deadpool. Superhero merupakan sosok yang memiliki kekuatan diluar nalar manusia dan mereka selalu menutupi identitasnya. Metode analisis semiotika Charles Sanders Pierce digunakan untuk meneliti tanda penggambaran pada tokoh Deadpool dalam film Deadpool. Melalui tanda-tanda yang muncul dalam film Deadpool, peneliti menemukan bahwa menjadi superhero tidak harus menjadi sosok yang sempurna baik fisik maupun sifatnya. Selain itu film ini mempertegas bahwa menjadi superhero hanya membutuhkan kemauan yang kuat, jiwa kepahlawanan yang besar dan usaha yang maksimal

Tailoring supercurrent confinement in graphene bilayer weak links

The Josephson effect is one of the most studied macroscopic quantum phenomena in condensed matter physics and has been an essential part of the quantum technologies development over the last decades. It is already used in many applications such as magnetometry, metrology, quantum computing, detectors or electronic refrigeration. However, developing devices in which the induced superconductivity can be monitored, both spatially and in its magnitude, remains a serious challenge. In this work, we have used local gates to control confinement, amplitude and density profile of the supercurrent induced in one-dimensional nanoscale constrictions, defined in bilayer graphene-hexagonal boron nitride van der Waals heterostructures. The combination of resistance gate maps, out-of-equilibrium transport, magnetic interferometry measurements, analytical and numerical modelling enables us to explore highly tunable superconducting weak links. Our study opens the path way to design more complex superconducting circuits based on this principle, such as electronic interferometers or transition-edge sensors

ELIE E-Learning in Engineering

In the Regins project ‘ELIE ’ classical design content is integrated in an elearning platform incorporating didactic principles in order to improve the education of future and present engineers. The prerequisites for the development and expansion of the e-learning platform with computer supported engineering tools and methods are also investigated. Topics in the field of traditional engineering design are still largely taught in the classic lessons form, i.e. lectures complemented by practical exercises (calculation tasks or small design tasks). However, the computer is an important means of work, particularly for the development and design of automotive products. Thus, the education of these engineers must be supplemented by computer supported tools and methods. Up to now, traditional design teaching and computer supported engineering methods are still largely taught separately. Increased efforts result from this-contents are covered twice because the connections between traditional teaching and the use of computers are not arranged optimally. Due to a lack of time, some applications cannot be taught at all, although they are already widely used in industry. The situation is further intensified by the tendency to reduce the weekly lecture time for students as a result of the Bologna declaration. Although the teaching design for engineers actually requires more time, less time is available

AUV navigation correction based on automated Multibeam Tile Matching

Ocean science and hydroacoustic seafloor mapping rely on accurate navigation underwater. By exploiting terrain information provided by a multibeam echosounder system, it is possible to significantly improve map quality. This article presents an algorithm capable of improving map quality and accuracy by aligning consecutive pings to tiles that are matched pairwise. A globally consistent solution is calculated from these matches. The proposed method has the potential to be used online in addition to other navigation solutions, but is mainly targeted for post processing. The algorithm was tested using different parameter settings on an AUV and a ship-based dataset. The ship-based dataset is publicly available as a benchmark. The original accurate navigation serving as a ground truth, alongside trajectories that include an artificial drift, are available. This allows quantitative comparisons between algorithms and parameter settings

Visualising geospatial time series datasets in realtime with the digital earth viewer

Highlights • The Digital Earth Viewer is an open-source (EUPL-licensed) hybrid application (desktop and server use) for the realtime visualisation and exploration of 4D geoscientific data. • Splitting the viewer into a natively compiled server-component optimized for maximum throughput and a web-technology-based client component geared towards maximum compatibility allows to harness the strengths of both platforms. • Desktop builds are release for Windows, Linux, and MacOS. • The Digital Earth Viewer has been used productively on expedition cruises to plan underwater exploration missions as all as a presentation and data validation tool by the GLODA-project. Abstract A comprehensive study of the Earth System and its different environments requires understanding of multi-dimensional data acquired with a multitude of different sensors or produced by various models. Here we present a component-wise scalable web-based framework for simultaneous visualisation of multiple data sources. It helps contextualise mixed observation and simulation data in time and space. This work is an extended version of the conference paper (Buck et al., 2021)