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A two-layer model for studying 2D dissolved pollutant runoff over impermeable surfaces
No full textDissolved pollutants in stormwater are a main contributor to water pollution in urban environments. However, many existing transport models are semi-empirical and only consider one-dimensional flows, which limit their predictive capacity. Combining the shallow water and the advection–diffusion equations, a two-dimensional physically based model is developed for dissolved pollutant transport by adopting the concept of a ‘control layer’. A series of laboratory experiments has been conducted to validate the proposed model, taking into account the effects of buildings and intermittent rainfalls. The predictions are found to be in good agreement with experimental observations, which supports the assumption that the depth of the control layer is constant. Based on the validated model, a parametric study is conducted, focusing on the characteristics of the pollutant distribution and transport rate over the depth. The hyetograph, including the intensity, duration and intermittency, of rainfall event has a significant influence on the pollutant transport rates. The depth of the control layer, rainfall intensity, surface roughness and area length are dominant factors that affect the dissolved pollutant transport. Finally, several perspectives of the new pollutant transport model are discussed. This study contributes to an in-depth understanding of the dissolved pollutant transport processes on impermeable surfaces and urban stormwater management
Transceiver Noise Characterization based on Perturbations
No full textIn this paper, a new technique for measuring transceiver noise, skew, and for the detection of uncompensated transceiver impairments is introduced. A Frequency domain notch or notches are applied at the transmitter, allowing an estimate of the Signal-to-Noise and Distortion Ratio (SNDR) at different stages over the transmission chain. The proposed technique requires to detect the signal spectrum such as: a modem receiver, an Optical Spectrum Analyzer (OSA), an oscilloscope, or an Electrical Spectrum Analyzer (ESA), depending on interface measured and requiring little processing of the received signal. We evaluate SNDR of Ciena's WaveLogic 4 commercial transceiver and a 95 Gbaud DAC. We demostrate that symmetrically disposed frequency domain notches can be used to eliminate the influence of crosstalk on the SNDR estimates. Finally, we show how a single notch spectrum can be used to detect and compensate for impairments, timing misalignments, and we perform skew estimation as an example
Understanding the influences of copd patient’s capability on the uptake of pulmonary rehabilitation in the uk through an inclusive design approach
No full textBackground: Pulmonary rehabilitation (PR) is recommended for patients with COPD to improve their symptoms and quality of life. However, in the UK, only one in ten of those who need PR receive it and this might be inaccessible to people with disabilities. This study aims to inform improvements to PR service by identifying barriers to the uptake of PR in the COPD care journey in relation to patients’ capabilities that can affect their access to PR. Methods: An Inclusive Design approach with mixed methods was undertaken. Firstly, patients and healthcare professionals were interviewed to gather insight into their experiences of COPD care and map patients’ care journey. Secondly, an Exclusion Calculator was used to estimate service demand on patients’ capability and the proportion of population excluded from the service. Thirdly, a framework analysis was applied to guide data analysis to identify the challenges of accessing PR. Finally, proposed recommendations were refined with patients and healthcare professionals. Results: The overall capability-related exclusion number was very high (62.5%), and exclusion caused by limited mobility was the highest (50%) among the interviewees and even higher based on the population database. This suggests the importance of considering COPD patients’ capability-related needs to improve their access to care. Capability-related challenges for patients accessing PR such as poor mobility to transport and low vision impairing ability to read inhaler instructions were identified, as well as non-capability-related challenges such as patients’ perception about COPD and inability to access proper information. Recommendations were proposed to help patients to self-manage their COPD and access to PR. Conclusion: Lack of attention to COPD patients’ capability level in the delivery of PR may affect its uptake. Considering the capability-related needs of COPD patients and providing patients with reassurance, information, and support on their care journey could improve the uptake of PR
Large Eddy simulation of a supersonic lifted hydrogen flame with perfectly stirred reactor model
No full textLarge Eddy Simulation with a Perfectly Stirred Reactor model (LES−PSR) is developed to simulate supersonic combustion with high-enthalpy flow conditions. The PSR model considers the viscous heating and compressibility effects on the thermo-chemical state, through correcting the chemical source term for progress variable and incorporating absolute enthalpy as the control variable for the look-up table. It is firstly validated by using a priori analysis of the viscous heating and compressibility effects. Then an auto-igniting hydrogen flame stabilized in supersonic vitiated co-flowing jet is simulated with LES−PSR method. The results show that the shock wave structure, overall flame characteristics, flame−shock interaction and lift-off height are accurately captured. Good agreements of the velocity and mixture fraction statistics with the experimental data are observed. The results also show that the LES−PSR model can predict the mean temperature and mole fractions of major species quite well in both flame induction and stabilization zones. However, there are some under-predictions of temperature RMS by about 100−150 K, which may be due to the chemical non-equilibrium in the H2/O2-enriched combustion product of the co-flowing jet. The scatter plots of two probe locations respectively from induction and flame zones show that the respective flame structures in mixture fraction space are captured well. However, the flucturations of the temperature and species mole fractions are under-predicted in the flame zone. The shock-induced auto-igniting spots are captured by the PSR model. These spots are highly unsteady and play an important role in flame stabilization. It is also shown that the intense reactions are initiated at mixture fractions around the stoichiometry or fuel-lean values, corresponding to local elevated pressure (1.5−2.0 atm) due to shock compression. The results also demonstrate that the pressure elevation is shown to have significant effects on the most reactive mixture fraction and shortest ignition delay time
Acoustics of the banjo: theoretical and numerical modelling
No full textA previous paper [J. Woodhouse et al. Acta Acustica 5, 15 (2021). https://doi.org/10.1051/aacus/ 2021009] showed acoustical measurements of an American 5-string banjo alongside similar measurements on a guitar, revealing a strong contrast in bridge admittance. Theoretical and numerical modelling is now presented to probe the physics behind this contrast. Without the bridge and strings, the banjo membrane has a rising trend of admittance associated with its modal density, and it has a distinctive pattern of sound radiation because an ideal membrane has no critical frequency. When the bridge and strings are added to the banjo, three formants shape the amplitude envelope of the admittance. One is associated with local effects of mass and stiffness near the bridge, and is sensitive to bridge mass and the break angle of the strings over the bridge. The other two formants are associated with dynamical behaviour of the bridge, analogous to the “bridge hill” in the violin
A unified Abaqus implementation of the phase field fracture method using only a user material subroutine
No full textWe present a simple and robust implementation of the phase field fracture method in Abaqus. Unlike previous works, only a user material (UMAT) subroutine is used. This is achieved by exploiting the analogy between the phase field balance equation and heat transfer, which avoids the need for a user element mesh and enables taking advantage of Abaqus' in-built features. A unified theoretical framework and its implementation are presented, suitable for any arbitrary choice of crack density function and fracture driving force. Specifically, the framework is exemplified with the so-called AT1, AT2 and phase field-cohesive zone models (PF-CZM). Both staggered and monolithic solution schemes are handled. We demonstrate the potential and robustness of this new implementation by addressing several paradigmatic 2D and 3D boundary value problems. The numerical examples show how the current implementation can be used to reproduce numerical and experimental results from the literature, and efficiently capture advanced features such as complex crack trajectories, crack nucleation from arbitrary sites and contact problems. The code developed can be downloaded from www.empaneda.com/codes
Failure Modes of a Laminated Composite with Complaint Interlayers
No full textComposites comprising a high-volume fraction of stiff reinforcements within a compliant matrix are commonly found in natural materials. The disparate properties of the constituent materials endow resilience to the composite, and here we report an investigation into some of the mechanisms at play. We report experiments and simulations of a prototype laminated composite system comprising silicon layers separated by polymer interlayers, where the only failure mechanism is the tensile fracture of the brittle silicon. Two failure modes are observed for such composites loaded in three-point bending: failure under the central roller in (i) the top ply (in contact with the roller) or (ii) the bottom ply (free surface). The former mode is benign with the beam retaining load carrying capacity, whereas the latter leads to catastrophic beam failure. Finite element (FE) simulations confirm this transition in failure mode and inform the development of a reduced order model. Good agreement is shown between measurements, FE simulations, and reduced order predictions, capturing the effects of material and geometric properties on the flexural rigidity, first ply failure mode, and failure load. A failure mechanism map for this system is reported that can be used to inform the design of such laminated composites
Inferring the effectiveness of government interventions against COVID-19
No full textGovernments are attempting to control the COVID-19 pandemic with nonpharmaceutical interventions (NPIs). However, the effectiveness of different NPIs at reducing transmission is poorly understood. We gathered chronological data on the implementation of NPIs for several European and non-European countries between January and the end of May 2020. We estimated the effectiveness of these NPIs, which range from limiting gathering sizes and closing businesses or educational institutions to stay-at-home orders. To do so, we used a Bayesian hierarchical model that links NPI implementation dates to national case and death counts and supported the results with extensive empirical validation. Closing all educational institutions, limiting gatherings to 10 people or less, and closing face-to-face businesses each reduced transmission considerably. The additional effect of stay-at-home orders was comparatively small
Quantum degeneracy and phase-space density in superradiant semiconductor heterostructures at room temperature
No full textWe investigate the fulfilment of the quantum degeneracy criterium in bulk GaAs/AlGaAs heterostructures operated under the superradiant emission generation at room temperature. The e-h density has been evaluated by analysing both spontaneous window emission from above the samples and amplified spontaneous emission radiated from their edges. The maximum experimental value of the phase-space density is 1.31 at T = 300 K. It is supposed that resonant photons with energies at the band gap establish coherence within the e-h ensemble and facilitate the build-up of a macroscopic wave packet from overlapped wave functions of collectively paired electrons and holes. As a result, the photon-mediated "stimulated"condensation of e-h pairs in phase space can take place at room temperature
Effect of Stack Geometry on the Dynamic Resistance Threshold Fields for Vertical Stacks of Coated Conductor Tapes
No full textThe expanding capabilities of HTS flux pumps and rectifiers to provide kA+ currents necessitates the exploration of high-current switching phenomenon. One such phenomenon, the dynamic resistance, occurs in type-II devices carrying dc transport currents while exposed to ac magnetic fields. In the following, finite element analysis of the threshold field for dynamic resistance in superconducting cables comprised of N tapes connected in parallel and stacked vertically is presented. Cables are modelled using the commercial software COMSOL and the H-formulation. The models employ Ic(B, θ) and n(B, θ) data obtained on short samples at 77 K as inputs to more accurately reflect the variation in local properties within the superconductor. The finite element results are then compared with calculations made using analytical models assuming a critical state. The finite element data closely resembles that predicted for a strip for a single tape, rapidly tending towards the slab result as N increases