MRC Laboratory of Molecular Biology
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Semiconducting few-layer PdSe<inf>2</inf> and Pd<inf>2</inf>Se<inf>3</inf>: Native point defects and contacts with native metallic Pd<inf>17</inf>Se<inf>15</inf>
No full textPdSe2 is a unique layered two-dimensional (2D) material with pentagonal structural motif and anisotropic properties. In addition, its strong interlayer interaction leads to new 2D form of the exfoliated monolayer, that is, Pd2Se3. Despite the increasing interest in these emerging 2D materials, the landscape of the native point defects, as a fundamental materials property, has not been revealed. In this work, we systematically investigate different types of defects in mono-and bi-layer PdSe2 and monolayer Pd2Se3. In contrast to the common expectation, Se vacancy is not the readily formed defect. Instead, Se-excess defects, such as SePd antisite and Se interstitial, are more likely to form over a majority of the allowed range of the atomic chemical potentials. Se-deficiency defect, Pd interstitial, is able to form under the Se-poor condition in bilayer PdSe2. The defect-mediated interlayer fusion model in the formation of monolayer Pd2Se3 from bilayer PdSe2 is reformulated. These dominant defects are found to stay in the neutral charge state, partly explaining the ambipolar behavior of the PdSe2 transistors. Finally, the stacked and lateral contacts between these few-layer semiconductors and the native Pd17Se15 metal are also studied. All these interfaces show p-Type contact properties. This work reveals the important materials properties of few-layer PdSe2 and Pd2Se3 for the better development of new functional devices
Detection of Railway Masts in Air-Borne LiDAR Data
No full textGenerating an object-oriented, geometric digital twin of an existing railway from its Point Cloud Data (PCD) is a laborious task, needing ten times more labour hours than scanning the physical asset. The resulting modelling cost counteracts the expected benefits of the twin. This cost and effort can be reduced by automating the process of creating such models. The first perceived challenge to achieving such automation is detecting masts from air-borne LiDAR data, as their position and function (separating substructure from superstructure) is critical to the subsequent detection of other elements. This paper presents a method that tackles the challenge above by leveraging the highly regulated and standardised nature of railways. In railway infrastructure, the geometric relations of a unit contain Overhead Line Equipment (OLE) between two mast pairs are consistent and repetitive throughout the track. Our method starts with tools for cleaning the PCD and roughly detecting its positioning and orientation. The resulting datasets are then processed by restricting the search region of the masts considering its positions compared to track centreline. Subsequently, the masts are detected using Random Sample Consensus (RANSAC) algorithm. The final deliverables of the method include the coordinates of the mast positions, detected point clusters and Three-Dimensional (3D) models of the masts in Industry Foundation Classes (IFC) format. We implemented the method in a prototype and tested it on three railway PCDs with a cumulative length of 18 km. The results indicated that the method achieves an overall detection rate of 94%. This is the first method in automatically detecting masts from air-borne LiDAR data
High-Power Femtosecond Pulse Generation from an All-Fiber Er-Doped Chirped Pulse Amplification System
No full textWe demonstrate a compact all-fiber Er-doped chirped pulse amplification (CPA) system that can produce ∼344 fs pulses with an average power of up to 1.02 W and a repetition rate of 40.6 MHz at 1.56 μm (corresponding to an energy of 25.1 nJ). The pulse compressor in the CPA system is based on a hollow core photonic crystal fiber which is directly butt-coupled to the silica fiber. A mismatched negative third-order dispersion is used to compensate the accumulated nonlinear phase shift in the amplification process for the first time, resulting in the generation of sub-400 fs pulses from an all-fiber Watt-level Er-doped CPA system. Our system architecture offers a possibility for ultrashort pulse generation from all-fiber Er-doped CPA lasers
A Novel Approach for Mixed Manual/Connected Automated Freeway Traffic Management.
No full textFreeway traffic management and control often rely on input from fixed-point sensors. A sufficiently high sensor density is required to ensure data reliability and accuracy, which results in high installation and maintenance costs. Moreover, fixed-point sensors encounter difficulties to provide spatiotemporally and wide-ranging information due to the limited observable area. This research exploits the utilization of connected automated vehicles (CAVs) as an alternative data source for freeway traffic management. To handle inherent uncertainty associated with CAV data, we develop an interval type 2 fuzzy logic-based variable speed limit (VSL) system for mixed traffic. The simulation results demonstrate that when more 10% CAVs are deployed, the performance of the proposed CAV-based system can approach that of the detector-based system. It is demonstrated in addition that the introduction of CAVs may make VSL obsolete at very high CAV-equipment rates
A Micro Resonant Electrometer with Single-Electron Charge Resolution at Room Temperature
No full textThe measurement of charge at single electron level at room temperature in analog and digital electronics is limited due to considerable thermal noise. In this work, we propose a method of charge detection with resolution of 0.17e/√Hz at room temperature by resonant electrometry based on tracking quasi-digital frequency shift of a force sensitive micromechanical oscillator stemming from the modal stiffness perturbation pertaining to charge input. We build a closed-loop system for the measurement and perform real-time monitoring of charge accumulation on the gate corresponding to 67 electrons per step. Analysis on thermomechanical noise suggests an ultimate threshold of charge resolution at the order of 10-4e/√Hz is possible benefitting from the high Q-factor of the resonator
The effect of real-time sensing of a window on energy efficiency, comfort, health and user behavior
No full textSensing technologies integration in buildings has grown rapidly. Most of them are connected to platforms for monitoring data and notifying anomalies, but few are integrated within building elements (either for data collection or response). These technologies help regulate HVAC, or detect building systems’ failures, but few enable passive sustainable strategies or space maintenance. It is possible to enhance building responsive operation by gathering granular data on passive systems’ operation and space occupation by setting a building component, that houses a sensor network. That is, if plugged into Building Information Models, it permits adaptation to unusual climate conditions or abrupt space use [Linked with the following correlated research projects: Research title: 2017, ELISIR. R&D+S&I Smart Living, R.L 26/2015 Widespread creative and technological manufacture 4.0 (ongoing)Research type: Funded by Regione LombardiaResponsible: Tiziana Poli (research unit, Politecnico di Milano).]
Push—pull microring-assisted space-and-wavelength selective switch
No full textWe introduce a novel design of a space-and-wavelength selective switch based on microring-assisted Mach–Zehnder interferometers. Multiple pairs of overcoupled microring resonators are incorporated as efficient and narrowband phase shifters and are driven in push–pull scheme. We design and demonstrate a 2 × 2 × 2λ elementary switch block with full spatial and spectral switching capabilities. The switching device’s cross talk suppression and extinction ratio both exceed 21 dB. We measure over 75 GHz optical bandwidth per channel and less than 1.5 dB power penalty at 10−9 BER when two 32 Gbps on–off keying signals are loaded simultaneously. This new class of switching elements can further enable compact and high-performance space-and-wavelength selective switch fabrics without the need for wavelength (de)multiplexers or parallel switching planes
Effect of Mesh Quality on Flux Reconstruction in Multi-dimensions
No full textTheoretical methods are developed to understand the effect of non-uniform grids on Flux Reconstruction (FR) in multi-dimensions. A better theoretical understanding of the effect of wave angle and grid deformation is established. FR is shown to have a smaller variation in properties than some finite difference counterparts. Subsequent numerical experiments on the Taylor–Green Vortex with jittered elements show the effect of localised regions of expansion and contraction. The effect this had on Nodal DG-like schemes was to increase the dissipation, whereas for more typical FR schemes the effect was to increase the dispersion. Some comparison is made between second-order FR and a second-order finite volume (FV) scheme. FR is found to be more resilient to mesh deformation, however, FV is found to be more resolved when operated at second order on the same mesh
Convolutional CRFs for semantic segmentation
No full textFor the challenging semantic image segmentation task the best performing models have traditionally combined the structured modelling capabilities of Conditional Random Fields (CRFs) with the feature extraction power of CNNs. In more recent works however, CRF post-processing has fallen out of favour. We argue that this is mainly due to the slow training and inference speeds of CRFs, as well as the difficulty of learning the internal CRF parameters. To overcome both issues we propose to add the assumption of conditional independence to the framework of fully-connected CRFs. This allows us to reformulate the inference in terms of convolutions, which can be implemented highly efficiently on GPUs. Doing so speeds up inference and training by two orders of magnitude. All parameters of the convolutional CRFs can easily be optimized using backpropagation. Towards the goal of facilitating further CRF research we have made our implementations publicly available
Mussel adhesive protein fused with VE-cadherin extracellular domain promotes endothelial-cell tight junctions and in vivo endothelization recovery of vascular stent
No full textImproving the surface properties of vascular stents to accelerate endothelialization in vivo could play an important role in minimizing the risk of late thrombosis. We previously showed that mussel adhesive protein fused with VE-cadherin extracellular domain (VE-M) specifically triggered endothelial cell adhesion in vitro. In this study, using stent implants coated with VE-M, we evaluated the clinical applicability of VE-M in endothelialization recovery in vivo. First, we explored the effect of VE-M on hemocompatibility and tight junctions between endothelial cells (ECs) in vitro. VE-M significantly inhibited platelet adhesion and promoted EC proliferation. Furthermore, VE-M drastically increased the centralization of F-actin in human umbilical vein endothelial cells (HUVECs) along the cell contacts, reduced fluorescein isothiocyanate (FITC)—dextran transport across the HUVECs, and elevated expression levels of tight junction proteins (TJPs) in ECs. We then evaluated the effect of VE-M on endothelialization recovery in vivo through implantation of vascular stents. At 1 day after implantation, stents coated with VE-M recruited more endothelial progenitor cells (EPCs) than bare stents. At 7 days after implantation, VE-M stents had a greater coverage of ECs than bare stents. At 1 month after implantation, ECs on VE-M stents were appropriately elliptical in morphology and closely resembled physiological morphology. Hematoxylin-eosin (HE) staining revealed little in-stent neointima formation on VE-M stents, and SEM images revealed that smooth endothelium had formed on VE-M stents without adherent platelets. Taken together, these findings indicate that VE-M accelerates in vivo endothelialization of vascular stents via recruitment of EPCs and promotes endothelium formation and could be explored as a potential bioactive coating for vascular implant. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:94–103, 2020