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Li H.,University of Electronic Science and Technology of China | Shao Z.,University of Electronic Science and Technology of China | Yeo S.,National University of Singapore | Leong Y.,Nanyang Technological University | Lim M.,ST Dynamics
Microwave and Optical Technology Letters | Year: 2011

A generalized high-order finite-difference method [discrete singular convolution-symplectic integrator propagator (DSCSIP)] is proposed to analyze the electromagnetic scattering problem in which the time difference is discretized by the SIP and the spatial difference by the DSC. When compared with the standard finitedifference time-domain (FDTD) method, the DSC-SIP method not only has higher stability and accuracy but also can save the computing memory space and CPU time with suitable meshes. Numerical examples are provided to show the high stability and effectiveness of the proposed method. © 2011 Wiley Periodicals, Inc.

Li H.,University of Electronic Science and Technology of China | Shao Z.,University of Electronic Science and Technology of China | Yeo S.P.,National University of Singapore | Lim M.H.,Nanyang Technological University | Leong Y.K.,ST Dynamics
2010 International Conference on Microwave and Millimeter Wave Technology, ICMMT 2010 | Year: 2010

A generalized higher-order finite-difference method (in which the time difference utilizes the symplectic integrator propagator and the spatial difference utilizes the discrete singular convolution) is proposed to analyze electromagnetic scattering from multiple targets. Numerical test results have demonstrated the higher stability and enhanced effectiveness of the proposed method when compared with the standard FDTD procedure. In addition, there are significant reductions in CPU time and memory space requirements when used with suitable meshes. © 2010 IEEE.

Birgersson E.,National University of Singapore | Tang E.H.,ST Dynamics | Lee W.L.J.,ST Dynamics | Sak K.J.,ST Dynamics
PLoS ONE | Year: 2015

During expiration, the carbon dioxide (CO2) levels inside the dead space of a filtering facepiece respirator (FFR) increase significantly above the ambient concentration. To reduce the CO2 concentration inside the dead space, we attach an active lightweight venting system (AVS) comprising a one-way valve, a blower and a battery in a housing to a FFR. The achieved reduction is quantified with a computational-fluid-dynamics model that considers conservation of mass, momentum and the dilute species, CO2, inside the FFR with and without the AVS. The results suggest that the AVS can reduce the CO2 levels inside the dead space at the end of expiration to around 0.4% as compared to a standard FFR, for which the CO2 levels during expiration reach the same concentration as that of the expired alveolar air at around 5%. In particular, during inspiration, the average CO2 volume fraction drops to near-to ambient levels of around 0.08% with the AVS. Overall, the time-averaged CO2 volume fractions inside the dead space for the standard FFR and the one with AVS are around 3% and 0.3% respectively. Further, the ability of the AVS to vent the dead-space air in the form of a jet into the ambient - similar to the jets arising from natural expiration without a FFR - ensures that the expired air is removed and diluted more efficiently than a standard FFR. © 2015 Birgersson et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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