MRC Laboratory of Molecular Biology
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On the potential for using bridge natural frequencies to detect scour: An experimental study
No full textMonitoring bridges for precursors of failure has the potential to improve their safety and resilience. However, the most prominent cause of bridge failure, scour, is difficult to monitor as it occurs underwater. The potential to identify scour by monitoring changes in the natural frequencies of a bridge is studied experimentally in this research. A field study was carried out on a bridge with preexisting scour confined to a section of a piled pier foundation, which was monitored throughout a repair process involving controlled backfilling of the scoured region, i.e. scour in reverse. The changes in natural frequency due to backfilling of the scour hole were unable to be captured experimentally as the estimated magnitudes (9% and 6 % for the first and second modes respectively) were of the same order as the variability of the natural frequency estimates. In order to study the relationship between natural frequency and scour in a more controlled environment, a geotechnical centrifuge experiment was conducted to simulate scour in a small-scale integral bridge model in dense sand. The model showed a significant (up to 40 %) change in natural frequency as a result of a scour depth equivalent to 30 % of the piled foundation depth. These experimental findings suggest that natural frequencies can potentially aid in detecting extensive bridge scour for piled foundations, but it may be challenging to detect localised scour limited to only a small portion of a foundation
Dual Voltage Flyback Topology Operation with Efficiency Enhancers at Dual Voltage Mains
No full textThis article introduces a Dual Voltage Flyback converter which overcomes the low efficiency of the conventional Flyback converter over universal mains voltages. The topology comprises of reconfigurable primary power loops enabled by additional state switches. This combination allows the converter to run in parallel or series modes, enhancing the performance at both 230Vac high line and 115Vac low line mains. It reduces the voltage rating of devices, supports two operating points that operate in boundary conduction mode under fixed frequency and improves the utilization of the devices. A 75W, 90Vac-265Vac to 24Vdc converter has been designed and tested. The converter is compatible with efficiency enhancement solutions such as synchronous rectifier and quasi-resonant control presented in this paper. The experimental results show that the proposed converter has a significant performance improvement at universal mains without any additional efficiency enhancer and considerable performance improvement when using synchronous rectifier compared to a conventional Flyback converter. However, solutions that reduce high voltage stress are less beneficial to the suggested topology
OASys: Envisioning an opto-electronic accelerator for deep learning applications
No full textWe propose OASys, an Opto-electronic Accelerator System, for efficient deep learning acceleration. The system takes on a full-stack architectural design approach and combines the power of Fourier optics and conventional FPGAs
Lanthanide-doped inorganic nanoparticles turn molecular triplet excitons bright
No full textThe generation, control and transfer of triplet excitons in molecular and hybrid systems is of great interest owing to their long lifetime and diffusion length in both solid-state and solution phase systems, and to their applications in light emission1, optoelectronics2,3, photon frequency conversion4,5 and photocatalysis6,7. Molecular triplet excitons (bound electron–hole pairs) are ‘dark states’ because of the forbidden nature of the direct optical transition between the spin-zero ground state and the spin-one triplet levels8. Hence, triplet dynamics are conventionally controlled through heavy-metal-based spin–orbit coupling9–11 or tuning of the singlet–triplet energy splitting12,13 via molecular design. Both these methods place constraints on the range of properties that can be modified and the molecular structures that can be used. Here we demonstrate that it is possible to control triplet dynamics by coupling organic molecules to lanthanide-doped inorganic insulating nanoparticles. This allows the classically forbidden transitions from the ground-state singlet to excited-state triplets to gain oscillator strength, enabling triplets to be directly generated on molecules via photon absorption. Photogenerated singlet excitons can be converted to triplet excitons on sub-10-picosecond timescales with unity efficiency by intersystem crossing. Triplet exciton states of the molecules can undergo energy transfer to the lanthanide ions with unity efficiency, which allows us to achieve luminescent harvesting of the dark triplet excitons. Furthermore, we demonstrate that the triplet excitons generated in the lanthanide nanoparticle–molecule hybrid systems by near-infrared photoexcitation can undergo efficient upconversion via a lanthanide–triplet excitation fusion process: this process enables endothermic upconversion and allows efficient upconversion from near-infrared to visible frequencies in the solid state. These results provide a new way to control triplet excitons, which is essential for many fields of optoelectronic and biomedical research
Identifying Critical Congestion Hotspots Using Network Approach: Smart Spatial Placement of Sensors
No full textIn this paper, a novel approach for identifying critical congestion hotspots based on network analysis using the automatic number plate recognition (ANPR) data in Cambridge, UK has been explored. This paper addresses use of conceptualized travel networks to reveal congestion patterns and the smart placement of camera sensors. The results of the study show that the travel network model can effectively identify critical congestion points. Using only 44% of the total cameras, the major congestion hotspots, including the junctions around the urban fringe were accurately captured. The current layout of the camera sensors was found to be redundant in several local areas. It is therefore suggested that, spatial optimization should be considered for sensor placement in the future. This study sheds new light on revealing urban mobility patterns in relation to travel networks and provide a heuristic tool for decision-makers for advancing smart digitalization in their cities
Laser-Driven Phase Segregation and Tailoring of Compositionally Graded Microstructures in Si-Ge Nanoscale Thin Films
No full textThe ability to manipulate the composition of semiconductor alloys on demand and at nanometer-scale resolutions is a powerful tool that could be exploited to tune key properties such as the electronic band gap, mobility, and refractive index. However, existing methods to modify the composition involve altering the stoichiometry by temporal or spatial modulation of the process parameters during material growth, limiting the scalability and flexibility for device fabrication. Here, we report a laser processing method for localized tailoring of the composition in amorphous silicon-germanium (a-SiGe) nanoscale thin films on silicon substrates, postdeposition, by controlling phase segregation through the scan speed of the laser-induced molten zone. Laser-driven phase segregation at speeds adjustable from 0.1 to 100 mm s-1 allows access to previously unexplored solidification dynamics. The steady-state spatial distribution of the alloy constituents can be tuned directly by setting the laser scan speed constant to achieve indefinitely long Si1-xGex microstructures, exhibiting the full range of compositions (0 < x < 1). To illustrate the potential, we demonstrate a photodetection application by exploiting the laser-written polycrystalline SiGe microstripes, showing tunability of the optical absorption edge over a wavelength range of 200 nm. Our method can be applied to pseudobinary alloys of ternary semiconductors, metals, ceramics, and organic crystals, which have phase diagrams similar to those of SiGe alloys. This study opens a route for direct laser writing of novel devices made of alloy microstructures with tunable composition profiles, including graded-index waveguides and metasurfaces, multispectral photodetectors, full-spectrum solar cells, and lateral heterostructures
SciPy 1.0: fundamental algorithms for scientific computing in Python
No full textSciPy is an open-source scientific computing library for the Python programming language. Since its initial release in 2001, SciPy has become a de facto standard for leveraging scientific algorithms in Python, with over 600 unique code contributors, thousands of dependent packages, over 100,000 dependent repositories and millions of downloads per year. In this work, we provide an overview of the capabilities and development practices of SciPy 1.0 and highlight some recent technical developments
REQUIREMENTS for DIAGRAMING in the DESIGN of MENTAL HEALTH DELIVERY SERVICES
No full textDelivering good quality mental health services remains a top priority in the English National Health Service (NHS). An approach to designing better delivery systems that takes into account the complexities of mental health services is highly desirable. This paper follows previous work that have sought to identify the key components of mental health delivery systems and explored the nature of the relationships between them. The paper presents the results of a qualitative thematic analysis of the requirements for diagrams as tools for describing and representing delivery systems in mental health
DESIGN MEETINGS: Towards AN UNDERSTANDING of the STAGES and ACTIVITIES THAT INFLUENCE SUCCESS
No full textA central part of the design process is collaboration, harnessing specialist expertise often in meetings. We understand relatively little about how meetings serve teams of designers and their work and this study uses soft systems methodology to attempt to create structures that describe and explain meetings. The results suggest extension of the boundary of interest and suggest a conceptual framework which reveals some under-addressed stages and activities which may help designers improve their meetings
Current density and Gate Ringing in Superjunction MOSFETs
No full textIt is common knowledge that the gate ringing of a power MOSFET is proportional to the dV/dt during the dynamic switching. In this study we show a particular situation when the gate ringing can be reduced significantly with a faster dV/dt. The faster dV/dt occurs when the driving current in the superjunction MOSFET increases, leading to faster charging of the parasitic capacitance. Initially, the gate ringing increases with the higher dV/dt. However, beyond a certain level the gate ringing starts to decline with further increase in the dV/dt. This abnormal phenomenon originates from the temporary turn-off the MOS channel during the turn-off transition