MRC Laboratory of Molecular Biology
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Prediction of premature cracking in jointed plain concrete pavements
No full textThis paper presents a mechanistic analysis of the occurrence and extent of premature cracking in jointed plain concrete pavements (JPCPs) by modeling (1) vehicle-pavement interaction, (2) foundation voiding, and (3) environmental conditions affecting pavement cracking. A finite-element (FE) pavement response model was developed to calculate the responses (stress and curling profile) of JPCPs. To characterize the loss of foundation support due to voids below concrete slabs, the nonlinear foundation model was linearized by spatially mapping the nonuniform modulus of subgrade reaction under the slabs. The linearized foundation model was incorporated into the pavement response model to evaluate the total flexural stress history in the slabs. A so-called quarter-vehicle model was used to calculate the dynamic tire force variation in response to a periodic surface profile caused by slab curl. Influence functions were used to combine the static elastic response of concrete slabs with the dynamic tire forces to determine the dynamic variations of surface stress and to predict fatigue cracking at various positions along the road. The initiation and propagation of premature longitudinal, transverse, and corner cracks was predicted using linear elastic fracture mechanics (LEFM). The study showed that dynamic tire forces have a significant effect on the location and magnitude of fatigue cracking in jointed concrete slabs. Cracking rates and the locations of peak stresses are affected by the combination of temperature gradient, vehicle characteristics and speed, slab properties, and foundation support. In addition, the occurrence of voids along the outer edge of pavements can lead to premature top-down longitudinal cracking and bottom-up transverse cracking
MgO-GGBS Binder-Stabilized/Solidified PAE-Contaminated Soil: Strength and Leachability in Early Stage
No full textThe MgO granulated ground blast-furnace slag (GGBS) binder, as a novel binder, has gained increasing attention in recent decades in stabilization/solidification (S/S) to treat contaminated soils. In this study, the physical strength and leaching performance of an MgO-GGBS (MG) binder was examined and compared with (PC) portland cement and PC and fly ash (PF) regarding the S/S treatment of dimethyl phthalates (PAE) contaminated soil after 7-day curing. PC, GGBS, fly ash (FA) and MgO were used as binders and the effect of different MG dosages was discussed. The results show that the order of early-stage strength after 7-day curing was: PF<MG<PC, and PAE leachate concentrations was in the order of MG<PC≈PF. The increase in MG dosage can improve the strength of binders and immobilize PAEs, while the increase of initial PAE concentrations (3,000-10,000 mg/kg) can reduce the strength and increase the leaching of PAE. Therefore, the MG binder showed a better performance for the S/S of PAE-contaminated soil than PC and PF binders. The relation between leachability and strength was further explored and is expected to provide guidance for the early-stage strength estimation after the S/S of PAE-contaminated clay soil with the MG binder
Ruddlesden Popper 2D perovskites as Li-ion battery electrodes
No full textHybrid metal halide perovskites, typically known for their photovoltaic applications, have recently gained traction as a potential energy-storage material due to their promising gravimetric capacities as lithium-ion battery electrode materials. Here we investigate the effect of tuning the layering properties of the quasi two-dimensional Ruddlesden Popper (RP) layered perovskite series (BA)2(MA)n-1PbnX3n+1 (BA-butylammonium, MA-methylammonium, X-halide (I- and Br-)) from n = 1 to n = 4 and the equivalent bulk crystal structure MAPbX3. The interaction between the insertion of lithium ions and the layering arrangement of the perovskite structure are studied electrochemically and compared to a reported three-stage energy storage mechanism in bulk perovskites. The layering structure that optimises both capacity and stability is determined to be n = 4, providing a compromise between the number of active layers and the lithium ion access between them provided by the BA organic chain, thus demonstrating initial and stabilised gravimetric capacities of 575.5 mA h g-1 and 89.9 mA h g-1 respectively. The effect of changing the halide within the perovskite structure is investigated and demonstrates a greater gravimetric capacity for the lighter bromide species compared to the commonly used iodide. Finally, high molarity electrolytes and tailored cut-off potentials are used to improve the stability of the RP layered perovskite electrodes
Split Parallel Semibridge Switching Cells for Full-Power-Range Efficiency Improvement
No full textThis paper proposes a positively-coupled-inductor (PCI) based paralleling scheme for semi-bridge switching cells which are formed by power MOSFETs and diodes. Both the semi-bridge switching cell and the inductor are split into two parallel parts, and thus, a small differential-mode inductance is formed between the midpoints of the parallel semi-bridge switching cells. A time-delay-based modulation strategy is applied to generate a controllable circulating current which enables all active switches to achieve the zero-current switching (ZCS) or zero-voltage switching (ZVS), and all diodes to achieve ZCS turn-off. Accordingly, the switching loss and the reverse-recovery loss can be significantly reduced. The operating principle of the proposed paralleling scheme is characterized by two complementary operation modes: desynchronized mode with soft-switching (lower switching loss) and synchronized mode with lower conduction loss. Compared with conventional soft-switching schemes, this solution features zero auxiliary switches, constant switching frequency, and improved full-power-range efficiency enabled by the dual operation modes. Furthermore, design guidelines of the PCIs are presented where a novel winding arrangement is proposed and verified to obtain a controllable differential mode (DM) inductance. The operation principles and advantages of the proposed paralleling structure are comprehensively validated on both Buck and Boost dc-dc converters with both Si and SiC power MOSFETs and diodes
Assimilation of Experimental Data to Create a Quantitatively Accurate Reduced-Order Thermoacoustic Model
No full textWe combine a thermoacoustic experiment with a thermoacoustic reduced order model using Bayesian inference to accurately learn the parameters of the model, rendering it predictive. The experiment is a vertical Rijke tube containing an electric heater. The heater drives a base flow via natural convection, and thermoacoustic oscillations via velocity-driven heat release fluctuations. The decay rates and frequencies of these oscillations are measured every few seconds by acoustically forcing the system via a loudspeaker placed at the bottom of the tube. More than 320,000 temperature measurements are used to compute state and parameters of the base flow model using the Ensemble Kalman Filter. A wave-based network model is then used to describe the acoustics inside the tube. We balance momentum and energy at the boundary between two adjacent elements, and model the viscous and thermal dissipation mechanisms in the boundary layer and at the heater and thermocouple locations. Finally, we tune the parameters of two different thermoacoustic models on an experimental dataset that comprises more than 40,000 experiments. This study shows that, with thorough Bayesian inference, a qualitative model can become quantitatively accurate, without overfitting, as long as it contains the most influential physical phenomena
Ignition probability and lean ignition behavior of a swirled premixed bluff body stabilized annular combustor
No full textAn experimental investigation was performed in a premixed annular combustor equipped with multiple swirl, bluff body burners to assess the ignition probability and to provide insights into the mechanisms of failure and of successful flame propagation. The experiments are done at conditions that are close to the lean blow-off (LBO) limit, and hence, the ignition is difficult and close to the limiting condition when ignition is not possible. Two configurations were employed, with 12 and 18 burners, the mixture velocity was varied between 10 and 30 m/s, and the equivalence ratio (/) between 0.58 and 0.68. Ignition was initiated by a sequence of sparks (2mm gap, 10 sparks of 10 ms each) and "ignition"is defined as successful ignition of the whole annular combustor. The mechanism of success and failure of the ignition process and the flame propagation patterns were investigated via high-speed imaging (10 kHz) of OH∗ chemiluminescence. The lean ignition limits were evaluated and compared to the LBO limits, finding the 12-burner configuration is more stable than the 18-burner. It was found that failure is linked to the trapping of the initial flame kernel inside the inner recirculation zone (IRZ) of a single burner adjacent to the spark, followed by localized quenching on the bluff body probably due to heat losses. In contrast, for a successful ignition, it was necessary for the flame kernel to propagate to the adjacent burner or for a flame pocket to be convected downstream in the chamber to grow and start propagating upward. Finally, the ignition probability (Pign) was obtained for different spark locations. It was found that sparking inside the recirculation zone resulted in Pign ~ 0 for most conditions, while Pign increased moving the spark away from the bluff body or placing it between two burners and peaked to Pign~ 1 when the spark was located downstream in the combustion chamber, where the velocities are lower and the turbulence less intense. The results provide information on the most favorable conditions for achieving ignition in a complex multiburner geometry and could help the design and optimization of realistic gas turbine combustors
Distributed Dynamic Measures of Criticality for Telecommunication Networks
No full textTelecommunication networks are designed to route data along fixed pathways, and so have minimal reactivity to emergent loads. To service today’s increased data requirements, networks management must be revolutionised so as to proactively respond to anomalies quickly and efficiently. To equip the network with resilience, a distributed design calls for node agency, so that nodes can predict the emergence of critical data loads leading to disruptions. This is to inform prognostics models and proactive maintenance planning. Proactive maintenance needs KPIs, most importantly probability and impact of failure, estimated by criticality which is the negative impact on connectedness in a network resulting from removing some element. In this paper, we studied criticality in the sense of increased incidence of data congestion caused by a node being unable to process new data packets. We introduce three novel, distributed measures of criticality which can be used to predict the behaviour of dynamic processes occurring on a network. Their performance is compared and tested on a simulated diffusive data transfer network. The results show potential for the distributed dynamic criticality measures to predict the accumulation of data packet loads within a communications network. These measures are predicted to be useful in proactive maintenance and routing for telecommunications, as well as informing businesses of partner criticality in supply networks
Reply to: Clinical interpretation of an interpretable prognostic model for patients with COVID-19
No full textInvestigating the electrical properties of different cochlear implants
No full textAim: This study characterises and compares electrical properties and current spread across four different makes of cochlear implants with differing electrode designs using a 3D-printed artificial cochlear model. Background: Cochlear implants are currently limited by current spread within the cochlea, which causes low spectral resolution of auditory nerve stimulation. Different cochlear implant makes vary in electrode size, shape, number, and configuration. How these differences affect cochlear implant current spread and function is not well known. Method: Each cochlear implant was inserted into a linear cochlear model containing recording electrodes along its length. Biphasic monopolar stimulation of each implant electrode was carried out, and the resultant waveform and transimpedance matrix (TIM) data obtained from the recording electrodes. This was repeated with each implant rotated 180 degrees in the cochlea model to examine the effects of electrode orientation. Impedance spectroscopy was also carried out at the apex, middle, and base of the model. Results: The four cochlear implants displayed similar TIM profiles and waveforms. One hundred eighty degrees rotation of each cochlear implant made little difference to the TIM profiles. Impedance spectroscopy demonstrated broad similarities in amplitude and phase across the implants, but exhibited differences in certain electrical parameters. Conclusion: Implants with different designs demonstrate similar electrical performance, regardless of electrode size and spacing or electrode array dimension. In addition, rotatory maneuvers during cochlear implantation surgery are unlikely to change implant impedance properties
Measurement and modelling of wall friction in the ram extrusion of stiff microcrystalline cellulose-based pastes
No full textSimulation of paste extrusion requires knowledge of the material–wall interactions and bulk deformation behaviour. A systematic approach to decoupling these is presented for a stiff paste, comprising microcrystalline cellulose/calcium carbonate/water, employing three different experimental configurations to separate paste-wall friction from bulk rheology. The bulk yielding behaviour was identified from ram extrusion testing with orifice dies, while wall friction was characterised using the twin-die extrusion apparatus reported by Bryan et al. [1]. Further extrusion tests with square and conical entry dies featuring various die land lengths provided data for comparison with simulations. The wall friction exhibited non-linear Navier slip with negligible pressure dependency: this relationship was included within a solid mechanics-based simulation of ram extrusion with ABAQUS. The estimate of the plastic yield stress from orifice die testing was refined using simulations of flow through square-entry dies and predicted the extrusion pressure for conical-entry dies with reasonable accuracy