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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
Impact of simplifications on numerical modelling of the shallow subsurface at city-scale and implications for shallow geothermal potential
No full textAnthropogenic infrastructures in the shallow subsurface, such as heated basements, tunnels or shallow geothermal systems, are known to increase ground temperatures, particularly in urban areas. Numerical modelling helps inform on the extent of thermal influence of such structures, and its potential uses. Realistic modelling of the subsurface is often computationally costly and requires large amounts of data which is often not readily available, necessitating the use of modelling simplifications. This work presents a case-study on the city centre of Cardiff, UK, for which high resolution data is available, and compares modelling results when three key modelling components (namely ground elevation, hydraulic gradient distribution and basement geometry) are implemented either ‘realistically’, i.e. with high resolution data, or ‘simplified’, utilising commonly accepted modelling assumptions. Results are presented at a point (local) scale and at a domain (aggregate) scale to investigate the impacts such simplifications have on model outputs for different purposes. Comparison to measured data at individual locations shows that the accuracy of temperature outputs from numerical models is largely insensitive to simplification of the hydraulic gradient distribution implemented, while changes in basement geometry affect accuracy of the mean temperature predicted at a point by as much as 3.5 °C. At the domain scale, ground temperatures within the first 20 m show a notable increase (approximately 1 °C volume-averaged and 0.5 °C surface-averaged), while the average heat flux over the domain is about 0.06 W/m2 at 20 m depth. These increased temperatures result in beneficial conditions for shallow geothermal utilisation, producing drilling cost savings of around £1700 per typical household system or about 9% increase in thermal energy potential. Simplifications of basement geometry and (to a lesser degree) the hydraulics can result in an overestimation of these temperatures and therefore over-predict geothermal potential, while the elevation simplification showed little impact
Chameleon graphene surfaces
No full textThe unique optical properties of graphene were combined with lithium-ion battery technology to produce multispectral optical devices, with colour-changing capabilities
Understanding, detecting and mitigating the efects of coactivations in ten-finger mid-air typing in virtual reality
No full textTyping with ten fngers on a virtual keyboard in virtual or augmented reality exposes a challenging input interpretation problem. There are many sources of noise in this interaction context and these exacerbate the challenge of accurately translating human actions into text. A particularly challenging input noise source arises from the physiology of the hand. Intentional fnger movements can produce unintentional coactivations in other fngers. On a physical keyboard, the resistance of the keys alleviates this issue. On a virtual keyboard, coactivations are likely to introduce spurious input events under a na ve solution to input detection. In this paper we examine the features that discriminate intentional activations from coactivations. Based on this analysis, we demonstrate three alternative coactivation detection strategies with high discrimination power. Finally, we integrate coactivation detection into a probabilistic decoder and demonstrate its ability to further reduce uncorrected character error rates by approximately 10% relative and 0.9% absolute
Enhanced Direct White Light Emission Efficiency in Quantum Dot Light-Emitting Diodes via Embedded Ferroelectric Islands Structure
No full textWhite light emission is of great importance in our daily life as it is the primary source of light indoor and outdoor as well as day and night. Among various materials and lighting technologies, intensive efforts have been made to quantum dots based-light-emitting diode (QD-LEDs, or QLEDs) because of outstanding optical properties, facile synthesis, and bandgap tunability of QDs. Despite the fact that QLEDs are able to present various colors in a visible range, realizing efficient direct white light emission is a challenge as white light emission can only be achievable through stacking and patterning of QD films or mixing of different sizes of QDs. This inevitably involves energy band mismatch at interfaces, leading to degradation of device performance. Here, a new effective method to improve white QLED performances through embedding a ferroelectric islands structure is introduced, which induces an electric field to effectively modulate the energy band at the junction interface. The formation of a favorable energy landscape leads to efficient charge transport, improved radiative recombination, and consequently high external quantum efficiency in the white QLEDs. In addition, it is demonstrated that this new approach is proved to be effective in different color temperatures ranging from 3000 to over 120 000 K