Vehicular emissions and concentrations in school zones: A case study

Recent research has revealed that human exposure to air pollutants such as CO, NO_x, and particulates can lead to respiratory diseases, especially among school-age children. Towards understanding such health impacts, this work estimates local-scale vehicular emissions and concentrations near a highway traffic network, where a school zone is located in. In the case study, VISSIM traffic micro-simulation is used to estimate the source of vehicular emissions at each roadway segment. The local-scale emission sources are then used as inputs to the California line source dispersion model(CALINE4) to estimate concentrations across the study area. To justify the local-scale emissions modeling approach, the simulation experiment is conducted under various traffic conditions. Different meteorological conditions are considered for emission dispersion. The work reveals that emission concentrations are usually higher at locations closer to the congested segments, freeway ramps and major arterial intersections. Compared to the macroscopic estimation(i.e. using network-average emission factors), the results show significantly different emission patterns when the local-scale emission modeling approach is used. In particular, it is found that the macroscopic approach over-estimates emission concentrations at freeways and under-estimations are observed at arterials and local streets. The results of the study can be used to compare to the US environmental protection agency(EPA) standards or any other air quality standard to further identify health risk in a fine-grained manner.

Numerical Methods for Two-Fluid Dispersive Fast MHD Phenomena

The finite volume wave propagation method and the finite element RungeKutta discontinuous Galerkin(RKDG)method are studied for applications to balance laws describing plasma fluids.The plasma fluid equations explored are dispersive and not dissipative.The physical dispersion introduced through the source terms leads to the wide variety of plasma waves.The dispersive nature of the plasma fluid equations explored separates the work in this paper from previous publications.The linearized Euler equations with dispersive source terms are used as a model equation system to compare the wave propagation and RKDG methods.The numerical methods are then studied for applications of the full two-fluid plasma equations.The two-fluid equations describe the self-consistent evolution of electron and ion fluids in the presence of electromagnetic fields.It is found that the wave propagation method,when run at a CFL number of 1,is more accurate for equation systems that do not have disparate characteristic speeds.However,if the oscillation frequency is large compared to the frequency of information propagation,source splitting in the wave propagation method may cause phase errors.The Runge-Kutta discontinuous Galerkin method provides more accurate results for problems near steady-state as well as problems with disparate characteristic speeds when using higher spatial orders.

Fourier domain optical coherence tomography with ultralong depth range

The depth ranges of typical implementations of Fourier domain optical coherence tomography （FDOCT）, including spectral domain OCT （SDOCT） and swept source OCT （SSOCT）, are limited to several millimeters. To extend the depth range of current OCT systems, two novel systems with ultralong depth range were developed in this study. One is the orthogonal dispersive SDOCT （OD-SDOCT）, and the other is the recirculated swept source （R-SS） interferometer/OCT. No compromise between depth range and depth resolution is required in both systems. The developed OD-SDOCT system realized the longest depth range （over 100 mm） ever achieved by SDOCT, which is ready to be modified for depth-encoded parallel imaging on multiple sites. The developed R-SS interferometer achieved submicron precision within a depth range of 30mm, holding potential in real-time contact-free on-axis metrology of complex optical sys- tems.