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How artificial intelligence and machine learning can help healthcare systems respond to COVID-19
No full textAbstractThe COVID-19 global pandemic is a threat not only to the health of millions of individuals, but also to the stability of infrastructure and economies around the world. The disease will inevitably place an overwhelming burden on healthcare systems that cannot be effectively dealt with by existing facilities or responses based on conventional approaches. We believe that a rigorous clinical and societal response can only be mounted by using intelligence derived from a variety of data sources to better utilize scarce healthcare resources, provide personalized patient management plans, inform policy, and expedite clinical trials. In this paper, we introduce five of the most important challenges in responding to COVID-19 and show how each of them can be addressed by recent developments in machine learning (ML) and artificial intelligence (AI). We argue that the integration of these techniques into local, national, and international healthcare systems will save lives, and propose specific methods by which implementation can happen swiftly and efficiently. We offer to extend these resources and knowledge to assist policymakers seeking to implement these techniques.</jats:p
Circuit Optimization of the HTS Transformer-rectifier Flux Pump
No full textFlux pumps are a type of wireless energizing device for superconducting systems. The dynamic resistance voltage in the flux pump are the main source for powering the superconducting system. But it can induce undesirable DC current in the circuit of flux pump. This paper discusses how to remove the induced undesirable DC current and improve the performance of the transformer-rectifier flux pump through the optimization of its circuit
Investigating excitonic physics in two-dimensional semiconductors by coherent two-dimensional microscopy
No full text© 2020 OSA - The Optical Society. All rights reserved. Excitonic interactions determine the photoelectric properties of two-dimensional semiconductors. By using spatially resolved coherent two-dimensional micro-spectroscopy, we are able to determine the strength of exciton-phonon coupling in single-layer MoSe2 at room temperature
Computer-generated fresnel holograms using field programmable gate arrays
No full textWe present a hardware architecture for generating Fresnel holograms for 3D holography on a small scale field-programmable gate arrays. Our hardware implementation can achieve similar performance to a high-end CPU enabled software implementation
Empirical assessment of the impact of VDC and Lean on environment and waste in masonry operations
No full textLean principles aim to improve construction through focus on value and waste elimination, which benefits environmental performance by reducing life cycle greenhouse gas (GHG) emissions and improving other environmental metrics. Although prior research identified relationships between Lean, BIM and sustainability, most studies were qualitative assessments of the value of lean and VDC management. In this study we measured the impact of Lean and VDC on waste in operations, and on GHG emissions, of masonry partitions. Researchers observed workers and classified their activities as value-adding or non-value-adding. Data from three different projects that include combinations of Lean and VDC implementation were used to estimate the efficiency of operations in comparison to earlier construction projects from 2007 to 2014 that implemented the same methods. The results were eye-opening: implementing Lean principles and VDC raised the proportion of value–adding activities to 68.4%, compared to only 35.8% in traditional management. Moreover, Lean and VDC methods contributed to reduce wasted global warming potential (GWP) from 169 kg CO2e/m3 of partition built to 112 kg CO2e/m3, an environmental improvement of 34%. Lean and VDC are dominant management approaches in reducing waste and improving sustainability
A KPI Based Performance Measurement Framework for Sri Lankan Construction Projects
No full textPerformance issues such as schedule delays, cost overruns, reduced quality, which lead to economic losses are common in the Sri Lankan construction industry. This paper presents a performance measurement framework (PMF) for contractors in Sri Lanka. Considering the local context, Key Performance Indicator (KPI) based system was chosen. By analyzing over thirty PMFs developed in different countries and through a set of interviews, eight areas were identified to be the most critical. For these areas, a set of fifteen KPIs was developed. From the list of KPIs and areas, the most important ones were shortlisted using Analytic Hierarchy Process (AHP) method. The main contribution of the study lies in developing one of the first PMFs applicable to construction projects in Sri Lanka taking inputs from the industry using methods such as AHP. It is expected that this PMF will help improve the overall performance levels in the construction industry of Sri Lanka
Development of an ultrafast laser ultra-precision machining platform
No full textUltra-precision manufacturing is commonplace in today’s society. It is used in a huge number of applications from electronics, medical devices to energy devices. Most devices manufactured using ultra-precision methods are made in high quantities where the volume of the components is required to outweigh the cost of the production equipment. However, there are few technologies targeting the manufacture of prototypes or small batches and those that are costly in terms of time or resources. Thus, there is a demand for a high speed, flexible manufacturing platform that is capable of ultra-precise manufacture. Currently, manufacturing techniques using ultrafast lasers are limited with regards to accuracy and repeatability. This body of work investigates how to develop an ultra-precision ultrafast laser manufacturing platform. From literature it was found that there are a significant number of avenues that could be investigated to improve the precision of an ultrafast laser machining process. This included the integration of metrology to perform closed-loop processing, studies of laser stability, new machining strategies and the effect of processing on plume formation. A significant proportion of the research presented was focused on the development of the ultra-precision platform. This work was carried out to provide a basis for this research but also for those that will use the platform in the future. One of the key outputs from this development was a graphical user interface that integrated with the range of devices on the platform such as the laser, 5-axis stage and beam diagnostic tools. This interface provides methods for automatic tilt correction, autofocus for the laser, angular ablation machining methods and other diagnostic tools. The interface is setup to capture the required data to provide traceability and diagnostics on the laser machining process. This aided the research carried out into improving the accuracy and repeatability of the laser-based process. First, an investigation into the characteristics of the laser installed on the ultra-precision platform was undertaken to determine the long-term stability of the laser with regards to the pointing stability, power stability and beam diameter stability. These characteristics are significant because they all affect the fluence at the focal spot which is responsible for ablating material. Variance in any of those parameters can have an effect and therefore influence the accuracy and repeatability of the process. The effect of duty cycle on power repeatability and the implications of this on machining was examined. Finally, a simulation was created to demonstrate the effect of laser stability on quality of machining. The ability to machine on angled planes enabled an investigation of the effect of angle on plume formation and the ablation threshold of the material. The ablation threshold for silicon was found at angles between normal and 45 degrees. It was found that the threshold could not be correlated with change of incident angle on the area of the focal spot. A range of different powers and angles were captured using the holographic camera and the effect on plume development was assessed. Overall, a range of tasks was completed which enabled several developments of the ultra-precision platform. These included in-process monitoring, the establishment of a novel machining strategy, and the capture of the effect of angular ablation on plume formation using a holographic camera. The platform is now placed to continue further development and integrate with other metrology technologies to provide closed-loop machining capabilities which will lead into a laser-based process which will be used for MEMS and similar device manufacture
Analysis of Implementation Methodologies of Deadbeat Direct-Torque and Flux Control (DB-DTFC) for IPMSMs in Stationary and Rotatory Reference Frames
No full textDeadbeat-control is a well-established control technique that uses the inverse machine model to determine the voltage commands required to achieve the desired torque and flux commands. Its classic implementation requires solving a quadratic equation with an extensive number of terms. Moreover, it can be only solved in the dq-reference frame. In this paper, two novel implementations are presented. The first methodology, in the dq-reference frame, reduces the algorithm's complexity and computation time. Moreover, it is immune to estimation errors of the permanent magnet flux. A second methodology based on the flux vector orientation is also presented. As opposed to the classic implementation, the proposed method does not require solving a quadratic equation; this reduces its complexity and computation time. Furthermore, the proposed methodology can be solved both in the dq and aß frames since it relies only on the stator flux's magnitude and angle. Up to date and to the best of the author's knowledge, DB-DTFC in the stationary frame has not been presented before for salient machines. DB-DTFC in the stationary frame reduces the reliance on the position observer and facilitates the implementation of overmodulation techniques and six-step operation. The proposed methodology can operate in the MTPF line without any adjustments and it shows an adequate dynamic performance. Simulation and experimental results validate the methodologies. Caveats regarding their implementation are also discussed
On the use of experimental ensembles in a hybrid deterministic-statistical energy analysis method
No full textThere is a clear need in modern industries for models that can predict the vibro-acoustic response of their manufactured products at the design stage. Models based on the hybrid deterministic-statistical method are a suitable solution to overcome the challenge of predicting the response of complex built-up systems in the mid-frequency range. Despite its advantages, this approach may face limitations when some of the system's properties are extremely difficult to model. This can be the case for the direct field dynamic stiffness, a key parameter in the hybrid method formulation, which depends on the type of junction assumed between the structural components of the system. This work explores the possibility of using experimental measurements to determine this dynamic stiffness. The proposed approach, based on statistical properties of random frequency response functions, is applied to the case of point junctions on a large thin plate. The results obtained using the new approach are compared to those computed using numerical techniques. It is concluded that the use of experimental data can be a suitable alternative to numerical techniques when modelling the junctions between components of a complex structure
Excitation Dynamics in Layered Lead Halide Perovskite Crystal Slabs and Microcavities
No full textLead halide perovskites are promising materials for various optoelectronic device applications such as solar cells, light-emitting diodes, and lasers. Three-dimensional perovskites, for example, CH3NH3PbI3 and CsPbBr3, have been demonstrated to be high-gain active media for low-threshold lasing. In contrast, layered perovskites, for example, (CH3(CH2)3NH3)2PbI4, are known to be difficult to show lasing oscillation especially at room temperature, despite their robustness for the environment. Here we reveal the bottleneck for the lasing oscillation in layered perovskites through systematic experiments on time-resolved photoluminescence and transient absorption. It is found that the energy transfer to a long-lived exciton state with triplet nature is enhanced by increasing pumping fluence or by introducing a high-Q microcavity, hindering the formation of population inversion. These results are consistent with a coupled rate-equation model as well as previous works and paves the way for designing low threshold layered perovskite lasers