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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Article
Earlier Faculty Research (2002)

The fundamental diagram is an important element in a variety of transportation studies. While various shapes of the fundamental diagram have been proposed and numerous debates on the best-fit fundamental diagram haven been made, why the fundamental diagram has many different shapes has not been well explained. This study introduces time gap as a key parameter to understand drivers’ behavioral differences at different locations and traffic conditions, then relate it to the shape of the fundamental diagram. From I-80 freeway event detector data, it is shown that time gap follows a certain probabilistic distribution and its mean value varies along locations. When downstream congestion is expected, drivers tend to take larger time gap than otherwise. It also turns out that divers take different time gaps for different travel speeds. Three different types of time gap-speed diagrams are identified and matched to Greenberg, reversed-lambda, and inverted-V types of fundamental diagrams, respectively.

    Cover page: An Empirical Study of the Time Gap and its Relation to the Fundamental Diagram
    • Article
    Earlier Faculty Research (2002)

    The fundamental diagram is an important element in a variety of transportation studies. While various shapes of the fundamental diagram have been proposed and numerous debates on the best-fit fundamental diagram have been made, why the fundamental diagram has many different shapes has not been well explained. This study introduces time gap as a key parameter to understand drivers' behavioral differences at different locations and traffic conditions, then relate it to the shape of the fundamental diagram. From I-80 freeway event detector data, it is shown that time gap follows a certain probabilistic distribution and its mean value varies along locations. When downstream congestion is expected, drivers tend to take larger time gap than otherwise. It also turns out that drivers take different time gaps for different travel speeds. Three different types of time gap-speed diagrams are identified and matched to Greenberg, reversed-lambda, and inverted-V types of fundamental diagrams, respectively.

      • Article
      Research Reports (2001)
      The control of a traffic corridor, which consists of two major component - freeway system control and arterial street system control, aims to improve flows on both freeway and arterial streets, and has been demonstrated as an effective means to increase the level of service of a corridor system during peak periods.  Ramp metering, or ramp control, has been considered to be a very important component of corridor traffic control.  Ramp metering is the application of control devices such as metering signals to limit the number of vehicles entering a freeway.  The fundamental philosophy of ramp metering is that the corridor can maintain its optimal operation by regulating the freeway demand to be under its capacity.  Maintaining the optimal operation of the corridor would provide congestion avoidance and accordingly travel time savings.
        Cover page: Evaluation of On-ramp Control Algorithms
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2015)
        Quaking (QKI) is a tumor-suppressor gene encoding a conserved RNA-binding protein, whose expression is downregulated in several solid tumors. Here we report that QKI plays an important role in the immune response and suppression of leukemogenesis. We show that the expression of Qki is reduced in lipopolysaccharide (LPS)-challenged macrophages, suggesting that Qki is a key regulator of LPS signaling pathway. Furthermore, LPS-induced downregulation of Qki expression is miR-155-dependent. Qki overexpression impairs LPS-induced phosphorylation of JNK and particularly p38 MAPKs, in addition to increasing the production of anti-inflammatory cytokine IL-10. In contrast, Qki ablation decreases Fas expression and the rate of Caspase3/7 activity, while increasing the levels of IL-1α, IL-1β and IL-6, and p38 phosphorylation. Similarly, the p38 pathway is also a target of QKI activity in chronic lymphocytic leukemia (CLL)-derived MEC2 cells. Finally, B-CLL patients show lower levels of QKI expression compared with B cells from healthy donor, and Qki is similarily downregulated with the progression of leukemia in Eµ-miR-155 transgenic mice. Altogether, these data implicate QKI in the pathophysiology of inflammation and oncogenesis where miR-155 is involved.
          Cover page: Quaking and miR-155 interactions in inflammation and leukemogenesis
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