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Open Access Publications from the University of California

Scholarly Works (5 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2019)

This dissertation develops a systematic model-based approach for the boundary control and estimation of freeway traffic congestion problem. Three topics of traffic congestion on a freeway segment are studied and include stop-and-go traffic oscillations, moving traffic shockwave, and downstream traffic bottleneck, which are governed by different partial differential equation (PDE) models and require the advancement and application of three PDE control techniques.

To supress stop-and-go oscillations, we introduce the macroscopic Aw-Rascle-Zhang traffic model, consisting of second-order nonlinear hyperbolic PDEs that govern dynamics of traffic density and velocity. The hetero-directional propagations of information in congested traffic generate the instabilities, motivating us to the stabilization problem for a coupled $2\times 2$ hyperbolic system. Using the backstepping method, a full-state feedback control is designed for ramp metering at outlet to actuate the outgoing traffic flow. We design boundary observer for state estimation and combine it with the full state feedback control to construct an output feedback controller. The observer design is validated with traffic field data. Under model parameter uncertainties, adaptive control design is proposed with on-line parameter estimation. Furthermore, we develop output feedback boundary control for two types of $4\times4$ nonlinear hyperbolic PDEs which arise from two-lane and two-class traffic congestion. Stabilization of two-lane traffic involves regulation of the lane-changing interactions with lane-specific varying speed limits while stabilization of two-class traffic tackles the heterogeneity of vehicles and drivers.

A moving traffic shockwave, caused by changes of local road situations, segregates light traffic upstream and heavy traffic downstream. This density discontinuity travels upstream. As a result, drivers caught in the shockwave experience transitions from free to congested traffic. The interface position is governed by an ordinary differential equation (ODE) dependent on the density of the PDE states, described with Lighthill-Whitham-Richards model. For the coupled PDE-ODE system, the predictor feedback design is applied to compensate the state-dependent input delays. We design bilateral boundary controllers to drive the moving shockwave front to a desirable setpoint position, hindering the upstream propagation of the traffic congestion.

Traffic on a freeway segment with capacity drop at outlet causes a downstream bottleneck. Traffic congestion forms because the traffic at the outlet overflows its capacity. Therefore the incoming flow of the segment needs to be regulated so that the outgoing traffic at the bottleneck area is discharged with its maximum flow rate. Since the traffic dynamics of the bottleneck is hard to model, we apply extremum seeking control, a model free approach for real-time optimization, to obtain the optimal input density at the inlet. The predictor feedback design is combined with the extremum seeking to compensate the delay effect of traffic state of the segment. The maximum flow rate is achieved at the bottleneck by regulating its upstream density at the inlet.

    Cover page: Boundary Control of Freeway Traffic Congestion
    • Article
    • Peer Reviewed
    UC Irvine Previously Published Works (2014)
    Particle Investigations at a Northern Ozarks Tower: NOx, Oxidant, Isoprene Research (PINOT NOIR) were conducted in a Missouri forest dominated by isoprene emissions from May to October 2012. This study presents results of new particle formation (NPF) and the growth of new particles to cloud condensation nuclei (CCN)-active sizes (∼100 nm) observed during this field campaign. The measured sub-5 nm particles were up to ∼20,000 cm-3 during a typical NPF event. Nucleation rates J1 were relatively high (11.0 ± 10.6 cm-3 s-1), and one order of magnitude higher than formation rates of 5 nm particles (J5). Sub-5 nm particle formation events were observed during 64% of measurement days, with a high preference in biogenic volatile organic compounds (BVOCs)- and SO2-poor northwesterly (90%) air masses than in BVOCs-rich southerly air masses (13%). About 80% of sub-5 nm particle events led to the further growth. While high temperatures and high aerosol loadings in the southerly air masses were not favorable for nucleation, high BVOCs in the southerly air masses facilitated the growth of new particles to CCN-active sizes. In overall, 0.4-9.4% of the sub-5 nm particles grew to CCN-active sizes within each single NPF event. During a regional NPF event period that took place consecutively over several days, concentrations of CCN size particles increased by a factor of 4.7 in average. This enhanced production of CCN particles from new particles was commonly observed during all 13 regional NPF events during the campaign period.
      Cover page: New Particle Formation and Growth in an Isoprene-Dominated Ozark Forest: From Sub-5 nm to CCN-Active SizesCreative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      UC Merced Previously Published Works (2016)
      Iron availability affects swarming and biofilm formation in various bacterial species. However, how bacteria sense iron and coordinate swarming and biofilm formation remains unclear. Using Serratia marcescens as a model organism, we identify here a stage-specific iron-regulatory machinery comprising a two-component system (TCS) and the TCS-regulated iron chelator 2-isocyano-6,7-dihydroxycoumarin (ICDH-Coumarin) that directly senses and modulates environmental ferric iron (Fe3+) availability to determine swarming initiation and biofilm formation. We demonstrate that the two-component system RssA-RssB (RssAB) directly senses environmental ferric iron (Fe3+) and transcriptionally modulates biosynthesis of flagella and the iron chelator ICDH-Coumarin whose production requires the pvc cluster. Addition of Fe3+, or loss of ICDH-Coumarin due to pvc deletion results in prolonged RssAB signaling activation, leading to delayed swarming initiation and increased biofilm formation. We further show that ICDH-Coumarin is able to chelate Fe3+ to switch off RssAB signaling, triggering swarming initiation and biofilm reduction. Our findings reveal a novel cellular system that senses iron levels to regulate bacterial surface lifestyle.
        Cover page: An iron detection system determines bacterial swarming initiation and biofilm formation
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2021)
        The construction of libraries of stereoisomers of natural products serves as an important approach to investigating the correlation between the stereostructure and biological activity. However, the total synthesis and isomerzation of polycyclic scaffolds with multiple chrial centers are rare. Spirooliganin (1), a new skeleton natural product isolated from the plant Illicium oligandrum, was structurally characterized by comprehensive analysis of NMR spectroscopic data and ECD which revealed an unprecedented 5-6-6-6-7 polycyclic framework with six chiral centers. Here we report a 17-step total synthesis to prepare a library of stereochemically diverse isomers of spirooliganin, including 16 diastereoisomers and 16 regioisomers. In addition to a regioselective hetero-Diels-Alder cycloaddition, the synthetic strategy involves a photo-induced stereoselective Diels-Alder reaction, which gives only the abnormal trans-fused product as rationalized by density functional theory calculations. Preliminary biological evaluation showed that spirooliganin and regioisomers 39 exhibited potent inhibition of Coxsackievirus B3. It also revealed the pharmacophore effect of the D-ring (16R,18R,24R, and 26R) for their antiviral activities.
          Cover page: Library construction of stereochemically diverse isomers of spirooliganin: their total synthesis and antiviral activity
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2017)
          This study sought to develop an automated segmentation approach based on histogram analysis of raw axial images acquired by light-sheet fluorescent imaging (LSFI) to establish rapid reconstruction of the 3-D zebrafish cardiac architecture in response to doxorubicin-induced injury and repair. Input images underwent a 4-step automated image segmentation process consisting of stationary noise removal, histogram equalization, adaptive thresholding, and image fusion followed by 3-D reconstruction. We applied this method to 3-month old zebrafish injected intraperitoneally with doxorubicin followed by LSFI at 3, 30, and 60 days post-injection. We observed an initial decrease in myocardial and endocardial cavity volumes at day 3, followed by ventricular remodeling at day 30, and recovery at day 60 (P < 0.05, n = 7-19). Doxorubicin-injected fish developed ventricular diastolic dysfunction and worsening global cardiac function evidenced by elevated E/A ratios and myocardial performance indexes quantified by pulsed-wave Doppler ultrasound at day 30, followed by normalization at day 60 (P < 0.05, n = 9-20). Treatment with the γ-secretase inhibitor, DAPT, to inhibit cleavage and release of Notch Intracellular Domain (NICD) blocked cardiac architectural regeneration and restoration of ventricular function at day 60 (P < 0.05, n = 6-14). Our approach provides a high-throughput model with translational implications for drug discovery and genetic modifiers of chemotherapy-induced cardiomyopathy.
            Cover page: Automated Segmentation of Light-Sheet Fluorescent Imaging to Characterize Experimental Doxorubicin-Induced Cardiac Injury and Repair.
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