published journal article
published journal article
working paper
This research seeks to determine the extent to which the Federal Energy Regulatory Commission’s policy of “Open Access” to natural gas pipelines has created competition in natural gas markets. We argue that recently developed cointegration techniques are the natural way to evaluate competition between natural gas spot markets at dispersed points in the national transmission network. We test daily spot prices between 190 market-pairs located in 20 producing fields and pipeline interconnections and find that the price series are not stationary and that most field markets were not cointegrated during 1987. By 1991, more than 65% of the markets had become cointegrated. The increased cointegration of prices is evidence that open access has has made gas markets more competitive.
working paper |
Oct 1993
working paper |
Jan 1997
book/book chapter |
Oct 1998
working paper |
Sep 1995
working paper |
Sep 1994
published journal article
Single-occupancy vehicles (SOVs) are charged to use the high-occupancy-toll (HOT) lanes, while high-occupancy-vehicles (HOVs) can drive in them at no cost. The pricing scheme for HOT lanes has been extensively studied at local bottlenecks or at the network level through computationally expensive simulations. However, the HOT lane pricing study on a freeway corridor with multiple origins and destinations as well as multiple interacting bottlenecks is a challenging problem for which no analytical results are available. This paper attempts to fill the gap by proposing to study the traffic dynamics in the corridor based on the relative space paradigm. In this new paradigm, the interaction of multiple bottlenecks and trips can be captured with Vickrey’s bathtub model by a simple ordinary differential equation. The paper considers three types of lane choice behavior and analyze their properties. Then, it proposes a distance-based dynamic pricing scheme based on a linear combination of I-controllers. This closed-loop controller is independent of the model and feeds back the travel time difference between HOT lanes and general-purpose lanes. Given the mathematical tractability of the system model, this study analytically studies the performance of the proposed closed-loop control under constant demand and show the existence and stability of the optimal equilibrium. Finally, the results were verified with numerical simulations considering a typical peak period demand pattern.
published journal article
conference paper
Carbon Nanotubes to Improve Short Glass Fiber Composites
published journal article
working paper
Reducing vehicle emissions levels is particularly important in the South Coast Air Basin of California, which includes the Los Angeles Metropolitan Area and the adjacent and interdependent Orange County, Riverside, and San Bernardino Metropolitan Areas. The climate and topography create ideal conditions for the area’s infamous smog; and cars, trucks and buses contribute 88 percent of carbon monoxide emissions and about 50 percent of the ozone components: oxides of nitrogen and reactive organic gases. It is apparent that air quality can be greatly improved if gasoline-powered personal vehicles can be replaced in substantial numbers by vehicles powered by electricity or alternative fuels, such as methanol, ethanol, propane, or compressed natural gas (CNG) (see Sperling, 1988 and National Research Council, 1990, for discussions of the environmental factors associated with specific alternative fuels). While none of these alternative fuels has zero-level emissions (even electricity, if generation is taken into account), they all have lower overall emissions levels than currently available gasoline and diesel fuels; they are considered “clean” fuels for the purposes of this market research study. Personal vehicles are defined for the purposes of the study to be cars or light trucks owned or leased by private individuals. The objective of this study is to determine the effect on personal vehicle purchase and fuel use of a few important attributes that potentially differentiate clean-fuel vehicles from conventional gasoline or diesel vehicles. By concentrating on quantitative estimation, it is intended that this study complement others aimed at qualitative assessments of the roles of information and uncertainty in consumer acceptance of clean-fuel vehicles (e.g., Turrentine and Sperling, 1991).
published journal article
BACKGROUND AND AIM: There is minimal evidence of relationships between maternal air pollution exposure and spontaneous premature rupture of membranes (SPROM), a critical obstetrical problem that can significantly increase maternal and fetal mortality and morbidity. No prior study has explored the PROM risk related to specific components of particulate matter with aerodynamic diameters of ≤ 2.5 µm (PM₂.₅). We examined associations between maternal exposure to nitrogen dioxide (NO₂), ozone (O₃), PM₂.₅, PM10, and PM₂.₅ constituents and SPROM. METHOD: A large retrospective cohort study was conducted and included 427,870 singleton live births from Kaiser Permanente Southern California during 2008-2018. Monthly averages of NO₂, O₃ (8-h daily maximum), PM₂.₅, and PM10 were measured using empirical Bayesian kriging based on measurements from monitoring stations. Data on PM₂.₅ sulfate, nitrate, ammonium, organic matter, and black carbon were obtained from a fine-resolution model. A discrete time approach with pooled logistic regressions was used to estimate associations throughout the pregnancy and based on trimesters and gestational months. The quantile-based g-computation models were fitted to examine the effects of 1) the air pollution mixture of four pollutants of interest and 2) the mixture of PM₂.₅ components. RESULTS: There were 37,857 SPROM cases (8.8%) in our study population. We observed relationships between maternal exposure to all four pollutants and SPROM. PM₂.₅ sulfate, nitrate, ammonium, and organic matter were associated with higher SPROM risks in the single-pollutant model. Mixture analyses demonstrated that the overall effects of the air pollution mixture and PM₂.₅ mixture in this study were mainly driven by O₃ and PM₂.₅ nitrate, respectively. Underweight mothers had a significantly higher risk of SPROM associated with NO₂. CONCLUSIONS: Our findings add to the literature on associations between air pollution exposure and SPROM. This is the first study reporting the impact of PM₂.₅ constituents on SPROM.
book/book chapter
