MRC Laboratory of Molecular Biology
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Quantum Emitter Localization in Layer-Engineered Hexagonal Boron Nitride.
No full textHexagonal boron nitride (hBN) is a promising host material for room-temperature, tunable solid-state quantum emitters. A key technological challenge is deterministic and scalable spatial emitter localization, both laterally and vertically, while maintaining the full advantages of the 2D nature of the material. Here, we demonstrate emitter localization in hBN in all three dimensions via a monolayer (ML) engineering approach. We establish pretreatment processes for hBN MLs to either fully suppress or activate emission, thereby enabling such differently treated MLs to be used as select building blocks to achieve vertical (z) emitter localization at the atomic layer level. We show that emitter bleaching of ML hBN can be suppressed by sandwiching between two protecting hBN MLs, and that such thin stacks retain opportunities for external control of emission. We exploit this to achieve lateral (x-y) emitter localization via the addition of a patterned graphene mask that quenches fluorescence. Such complete emitter site localization is highly versatile, compatible with planar, scalable processing, allowing tailored approaches to addressable emitter array designs for advanced characterization, monolithic device integration, and photonic circuits
COVID-19 crisis management in Luxembourg: Insights from an epidemionomic approach
No full textWe develop an epidemionomic model that jointly analyzes the health and economic responses to the COVID-19 crisis and to the related containment and public health policy measures implemented in Luxembourg. The model has been used to produce nowcasts and forecasts at various stages of the crisis. We focus here on two key moments in time, namely the deconfinement period following the first lockdown, and the onset of the second wave. In May 2020, we predicted a high risk of a second wave that was mainly explained by the resumption of social life, low participation in large-scale testing, and reduction in teleworking practices. Simulations conducted 5 months later reveal that managing the second wave with moderately coercive measures has been epidemiologically and economically effective. Assuming a massive third (or fourth) wave will not materialize in 2021, the real GDP loss due to the second wave will be smaller than 0.4 percentage points in 2020 and 2021
Numerical Study on Ring-shape Superconducting Trapped Field Magnet Based on Circuit Model
No full textThe so-called ring-shape superconducting trapped field magnet has been proved as a potential candidate to replace commercial permanent magnets in practical industrial applications on account of its jointless structure. In this paper, a circuit method based on Bean model, E-J power law and Faraday law has been built to investigate the magnetization mechanism of ring-shape magnet. The field dependent critical current of superconducting materials has been taken into consideration for further optimization. The numerical model was verified by both finite element method (FEM) and experiments. Compared with other methods, the circuit-based simulation method has the advantages of high efficiency, fast speed and wide applicability. On basis of this method, the paper also studied characteristics of ring-shape magnets under different working conditions to provide a guideline for the magnet design
Capabilities and Limitations of the Quadratic Constitutive Relation in Corner Flow Prediction
No full textThe capabilities and limitations of the quadratic constitutive relation in computing streamwise corner flows are investigated using publicly-available data from direct numerical simulations of a square duct flow. The increased accuracy of RANS computations which use the quadratic constitutive relation in corner flows is not due to significantly improved turbulent stress estimates in general. Instead, the reported success of the relation in this flow field, whose structure is governed by the presence of streamwise vortices, is a result of the particular turbulent stress combinations which appear in the mean streamwise vorticity equation being better predicted. Despite this improved prediction, the precise topology of the vorticity production terms deviates from the true distribution, particularly close to the walls, which explains why the strength and position of the corner vortices may not quite correspond to those in the physical flow. In addition, the imperfect estimate of the shear stress term is observed to be the source of additional, non-physical vortices when the QCR coefficient exceeds its recommended value
Supporting physical and mental health rehabilitation at home with virtual reality headsets and force feedback gloves
No full textThe outbreak of COVID-19 has led to worldwide quarantines and telehealth has become the lifeline for patients prone to infection. We propose using a Virtual Reality (VR) system as a playful coping strategy for rehabilitation at home. We hypothesize such a system can improve the physical and mental well-being of the user during play. In this demonstration, we transform the therapy into a playful virtual cat bathing simulation using a VR headset coupled with force feedback gloves. This results in an engaging and feedback-rich scenario where users practice fine motor skills by progressively completing three cat-care tasks
Concept Design of a Portable Superconducting Transformer Based on Conductors in Tube Cables
No full textPortable substations based on large capacity transformers have shown great advantages for practical demand from natural disaster area and remote area, as well as the short-term power grid maintenance. However, the capacity of traditional portable transformer is restricted by transportation weight limit in the application area. In this paper, concept design of a 110 kV/63 MVA superconducting transformer with compact size and light weight is presented. The superconducting materials used in this transformer are all in structure of a so-called conductors in tube (CIT) cable. Firstly, the electrical design of portable transformer is carried out by using traditional transformer design manual. Then, both simulations and experiments are carried out to verify the feasibility of CIT cables. Finally detail design of CIT cables for both high voltage winding and low voltage winding are presented based on finite element method
Ramping Loss Analysis of No-insulation HTS Coil under External Field Using an Improved Equivalent Circuit Model
No full textAbstractThis paper is to study the ramping loss of no-insulation (NI) high temperature superconducting (HTS) racetrack coil under different external magnetic fields during the charging process. An improved equivalent circuit electromagnetic coupling model for the HTS racetrack coil is introduced with good computational speed and accuracy. The simulation results show that the turn-to-turn loss and the change of the lowest critical current position are obviously influenced by the external field that have not been mentioned from our knowledge base. During the rising time of the power supply current, there is little difference in current distribution under different external fields. But after that, steady state of charging process is deeply influenced by the external field. A larger external field will lead to a lower charging current and the external bypass phenomenon. Another result is that the relationship between direction of external field and orientation of coils will influence the lowest critical current amount and position. The relationship between turn-to-turn resistivity of co-winding materials and ramping loss is also discussed in the paper. The distributed unevenness and value of the turn-to-turn loss change with the increase of turn-to-turn resistivity
Operation and performance of the 4H-SiC junctionless FinFET
No full textThis work presents a comprehensive study on the behaviour and operation of a vertical 1.2 kV 4H-SiC junctionless power FinFET. The increased bulk conduction in the channel of this topology may bring reductions in the channel resistance compared to trench MOSFETs, whose performance is limited by the high interface state density. For this purpose, finite element (FE) simulations are used to examine the operation of this device. It is hence demonstrated that the junctionless FinFET can attain a high average channel drift mobility well above 100 cm2/(Vs), leaving the resistance to be determined by the drift and substrate regions. This allows the FinFET to turn on and reach its steady state current using a much (> 3x) smaller gate overdrive than standard designs. On the other hand, however, the overly high field in the gate oxide, the lack of an efficient mechanism for hole extraction, and the low threshold voltage can cause significant reliability issues. Furthermore, it is shown that the high input capacitance of the FinFET can limit its switching speed to slower levels than in standard trench MOSFETs, which raises the need for further development of the original design proposed for vertical GaN devices. In this context, it is demonstrated that the addition of a p-shield below the trenches can alleviate the off-state reliability issues and increase the speed, while still maintaining a competitive Ron ∼ 2mΩ cm2 even without the use of n-JFET enhancement doping
Ion exchange in atomically thin clays and micas.
No full textThe physical properties of clays and micas can be controlled by exchanging ions in the crystal lattice. Atomically thin materials can have superior properties in a range of membrane applications, yet the ion-exchange process itself remains largely unexplored in few-layer crystals. Here we use atomic-resolution scanning transmission electron microscopy to study the dynamics of ion exchange and reveal individual ion binding sites in atomically thin and artificially restacked clays and micas. We find that the ion diffusion coefficient for the interlayer space of atomically thin samples is up to 104 times larger than in bulk crystals and approaches its value in free water. Samples where no bulk exchange is expected display fast exchange at restacked interfaces, where the exchanged ions arrange in islands with dimensions controlled by the moiré superlattice dimensions. We attribute the fast ion diffusion to enhanced interlayer expandability resulting from weaker interlayer binding forces in both atomically thin and restacked materials. This work provides atomic scale insights into ion diffusion in highly confined spaces and suggests strategies to design exfoliated clay membranes with enhanced performance