MRC Laboratory of Molecular Biology
CUED - Cambridge University Engineering DepartmentNot a member yet
45551 research outputs found
Sort by
Almost global convergence to practical synchronization in the generalized Kuramoto model on networks over the n-sphere
No full textFrom the flashing of fireflies to autonomous robot swarms, synchronization phenomena are ubiquitous in nature and technology. They are commonly described by the Kuramoto model that, in this paper, we generalise to networks over n-dimensional spheres. We show that, for almost all initial conditions, the sphere model converges to a set with small diameter if the model parameters satisfy a given bound. Moreover, for even n, a special case of the generalized model can achieve phase synchronization with nonidentical frequency parameters. These results contrast with the standard n = 1 Kuramoto model, which is multistable (i.e., has multiple equilibria), and converges to phase synchronization only if the frequency parameters are identical. Hence, this paper shows that the generalized network Kuramoto models for n ≥ 2 displays more coherent and predictable behavior than the standard n = 1 model, a desirable property both in flocks of animals and for robot control
Optimal control and energy storage for DC electric train systems using evolutionary algorithms
No full textElectrified railways are becoming a popular transport medium and these consume a large amount of electrical energy. Environmental concerns demand reduction in energy use and peak power demand of railway systems. Furthermore, high transmission losses in DC railway systems make local storage of energy an increasingly attractive option. An optimisation framework based on genetic algorithms is developed to optimise a DC electric rail network in terms of a comprehensive set of decision variables including storage size, charge/discharge power limits, timetable and train driving style/trajectory to maximise benefits of energy storage in reducing railway peak power and energy consumption. Experimental results for the considered real-world networks show a reduction of energy consumption in the range 15%–30% depending on the train driving style, and reduced power peaks
Design and model for ‘falling particle’ biosensors
No full textParticle-immobilized enzymes have proven benefits when integrated into biosensors, typically via packed-bed approaches in microfluidic channels. These benefits include dramatically improving sensitivity by increasing the effective surface area to volume ratio and enhancing shelf-life through their thermal stability. However, microfluidic approaches require complex fabrication steps to create weirs or pillars that hold the particles in place and an external pump to control sample flow. In a global trend for affordable diagnostics, there is a need to benefit from the improved performance of particle-based systems while also simplifying the fabrication and readout techniques. Here, we present a new biosensor format, where the bio-functionalized particles are moved through the fluid sample in which they are suspended. We deliver a first study into the main design considerations for this falling particle biosensor, detailing the interdependencies between the kinetics of the enzyme reaction, the mass transport of the substrate to the enzyme on the surface of the particle, and the falling behavior of the settling particles. We detail, through a mathematical model, validated by experimental results, how particle size and enzyme loading are able to influence the outcome measured and establish that this falling particle model does not deviate from the kinetic regime, but that particle size and enzyme loading can be used to tune the signal resolution and deliver simple but highly effective sensors
Accelerated measurements of aerosol size distributions by continuously scanning the aerodynamic aerosol classifier
No full textUsing an Aerodynamic Aerosol Classifier (AAC) upstream of a particle detector is a relatively new method for measuring the aerodynamic size distribution of an aerosol. This approach overcomes limitations of previous methodologies by leveraging the high transmission efficiency, independence from particle charging, and adjustable classification range and resolution of the AAC. However, the AAC setpoint must be stepped and stabilized before each measurement, which forces tradeoffs between measurement time and step resolution. This study is the first to develop and validate theory which allows the speed of the AAC classifier to be continuously varied (following an exponential function), rather than stepped. This approach reduces measurement time, while increasing the resolution of the measured distribution. Assuming uniform axial flow, the transfer function of the scanning AAC and its inversion are determined. Limited trajectory theory is used to derive the idealized transfer function of the scanning AAC, while parameterized, particle streamline theory is used to develop the non-idealized transfer function, which accounts for non-idealized particle and flow behaviors within the classifier. This theory and the practical implementation of the scanning AAC are validated by the high agreement of its measurements of polystyrene latex (PSL) particles (within 8.7% for six sizes between 100 nm to 2.02 μm), and of size distributions of three aerosol sources (Bis(2-Ethylhexyl) sebacate, NaCl and soot) to those measured by the stepping AAC (within 2% or better if the source stability is considered). The validity of assuming uniform axial flow in the classifier and downstream plumbing/detector are also discussed. Copyright © 2020 American Association for Aerosol Research
Dynamic soil-structure interaction of a shallow founded shear frame and a frame equipped with viscous dampers under seismic loading
No full textIt is not uncommon for buildings requiring good seismic performance, with objectives of immediate occupancy and continuous operation, to be equipped with supplemental damping devices. Oil dampers are a popular type of velocity-dependant devices that can be fitted into a structure without incurring considerable changes to the frame stiffness. Seminal experimental work into the seismic performance of structures with viscous dampers is based primarily on large-scale testing of prototype frames fixed to rigid shaking tables overlooking ground flexibility effects. Most literature examining the effects of soil-structure interaction (SSI) on the behaviour of structures with viscous dampers use highly idealised representations of the foundation-soil system stiffness and damping characteristics. This paper utilises high gravity dynamic centrifuge testing to investigate the effects of different base fixity conditions on the seismic behaviour of two model shear structures; one fitted with miniature oil dampers and one left bare for comparison. The base fixity conditions replicated are full base fixity and shallow embedment into dry, dense and loose sand. Experimental results indicate that the damped frame is less responsive to changes in ground compliance relative to its bare frame counterpart. Any apparent drop in damper control with reduced base fixity is driven by improvements in the seismic performance of the bare frame benchmark rather than an increase in the dynamic response of the damped structure. Despite the adverse effects of reduced base fixity on the energy dissipated by the dampers, SSI did not negatively affect the performance of the damped frame
The Influence of Strut Waviness on the Tensile Response of Lattice Materials
No full textRecent advances in additive manufacturing methods make it possible, for the first time, to manufacture complex micro-architectured solids that achieve desired stress versus strain responses. Here, we report experimental measurements and associated finite element (FE) calculations on the effect of strut shape upon the tensile response of two-dimensional (2D) lattices made from low-carbon steel sheets. Two lattice topologies are considered: (i) a stretching-dominated triangular lattice and (ii) a bending-dominated hexagonal lattice. It is found that strut waviness can enhance the ductility of each lattice, particularly for bending-dominated hexagonal lattices. Manufacturing imperfections such as undercuts have a small effect on the ductility of the lattices but can significantly reduce the ultimate tensile strength. FE simulations provide additional insight into these observations and are used to construct design maps to aid the design of lattices with specified strength and ductility
Neutronic and thermal-hydraulic fuel design for a dual-salt breed-and-burn molten salt reactor
No full textA breed-and-burn molten salt reactor (BBMSR) concept is proposed to achieve high uranium utilisation in a once-through fuel cycle. By using separate fuel and coolant molten salts, the BBMSR may overcome key materials limitations of traditional breed-and-burn (B&B) and molten salt reactor designs. A central challenge in design of the BBMSR fuel is balancing the neutronic requirements for B&B operation with thermal-hydraulic requirements for safe and economically competitive reactor operation. Fuel configurations that satisfy both neutronic and thermal-hydraulic objectives were identified for 5% enriched and 20% enriched uranium feed fuel. A neutron balance method and thermal-hydraulic design algorithm were used to evaluate uranium utilisation and maximum allowable power density, respectively, for a range of configurations. B&B operation is achievable in the 5% enriched version with orders of magnitude greater uranium utilisation compared to light water reactors, but with moderately lower power density. Using 20% enriched feed fuel relaxes neutronic constraints so a wider range of fuel configurations can be considered, but there is a strong inverse correlation between power density and uranium utilisation. The fuel design study indicates the flexibility of the BBMSR concept to operate along a spectrum of modes ranging from high fuel utilisation at moderate power density using 5% enriched uranium feed fuel, to high power density and moderate utilisation using 20% uranium enrichment
First UK Commercial Deployment of Microcapsule-Based Self-Healing Reinforced Concrete
No full textConsolidating previous research on the development of novel microcapsules for self-healing in cementitious systems, this work forms a base for developing an implementation strategy and guidance for microcapsule-based self-healing technology. The study presents details of the first commercial deployment of this technology, as a ready-mix self-healing additive for commercial application. This involved the on-site construction of two slabs in a new development at the University of Cambridge. This paper describes the optimization of the mix, the structural concept and design, and processing and casting procedures. Prior to application, the compliance and compatibility of the healing additive with the concrete according to specifications and requirements of the design were investigated, validating the use of the developed system. These were complemented by large-scale laboratory testing of the healing efficiency under damage scenarios identified as critical for the on-site application. The performance of the site installation was monitored over 12 months through a combination of nondestructive testing methods. Results are presented with durability indicators confirming the in situ enhanced performance of the proposed self-healing system
Plasmon-Induced Trap State Emission from Single Quantum Dots
No full textCharge carriers trapped at localized surface defects play a crucial role in quantum dot (QD) photophysics. Surface traps offer longer lifetimes than band-edge emission, expanding the potential of QDs as nanoscale light-emitting excitons and qubits. Here, we demonstrate that a nonradiative plasmon mode drives the transfer from two-photon-excited excitons to trap states. In plasmonic cavities, trap emission dominates while the band-edge recombination is completely suppressed. The induced pathways for excitonic recombination not only shed light on the fundamental interactions of excitonic spins, but also open new avenues in manipulating QD emission, for optoelectronics and nanophotonics applications
MorphFace: A Hybrid Morphable Face for a Robopatient
No full textPhysicians use pain expressions shown in a patient's face to regulate their palpation methods during physical examination. Training to interpret patients' facial expressions with different genders and ethnicities still remains a challenge, taking novices a long time to learn through experience. This letter presents MorphFace: a controllable 3D physical-virtual hybrid face to represent pain expressions of patients from different ethnicity-gender backgrounds. It is also an intermediate step to expose trainee physicians to the gender and ethnic diversity of patients. We extracted four principal components from the Chicago Face Database to design a four degrees of freedom (DoF) physical face controlled via tendons to span ∼85% of facial variations among gender and ethnicity. Details such as skin colour, skin texture, and facial expressions are synthesized by a virtual model and projected onto the 3D physical face via a front-mounted LED projector to obtain a hybrid controllable patient face simulator. A user study revealed that certain differences in ethnicity between the observer and the MorphFace lead to different perceived pain intensity for the same pain level rendered by the MorphFace. This highlights the value of having MorphFace as a controllable hybrid simulator to quantify perceptual differences during physician training