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Open Access Publications from the University of California

Scholarly Works (11 results)

  • Article
Earlier Faculty Research (2002)

The deregulation experience in airline, banking, and telecommunication suggests that the heterogeneity in consumers’ preferences has important policy significance. However, the varied nature in motorists’ preferences has been hardly recognized in urban passenger transportation sector. In this public sector, the public authority generally offers a uniform class of services to all potential users. This dissertation employs the new advances in econometrics on survey data sets from road pricing experiment in Los Angeles area to study the diversity in motorists’ preferences for travel time and travel time reliability. The empirical findings are used to explore the efficiency and distributional effects of road pricing that accounts for users’ heterogeneity.

This dissertation found substantial heterogeneity in motorists’ preferences for both travel time and travel time reliability. Furthermore, based on a simulation model, this dissertation found that road pricing policies catering to varying preferences can substantially increase efficiency while maintaining the same political feasibility as the current experiments. This dissertation also explores how to apply the recent developments in Bayesian econometrics to estimate the multinomial probit models combining different sources of data, which can be used to estimate the diversity in peoples’ preferences with more flexibility in model specification.

    Cover page: Heterogeneity in Motorists' Preferences for Time Travel and Time Reliability: Empirical Findings from Multiple Survey Data Sets and Its Policy Implications
    • Article
    Earlier Faculty Research (2001)

    Some road-pricing demonstrations use “value pricing,” in which travelers can choose between a free but congested roadway and a priced roadway. Recent research has uncovered a potentially serious problem for such demonstrations, second-best tolls may be far lower than those typically charged, and from a welfare perspective, the latter may be worse than not pricing at all. That research, however, assumes that all travelers are identical and it therefore neglects the benefits of product differentiation. Using a model with two user groups, we find that accounting for heterogeneity in value of time as important in evaluating constrained policies, and improves the relative performance of policies that offer differential prices.

      Cover page: The Value of "Value Pricing" of Roads: Second-Best Pricing and Product Differentiation
      • Article
      Working Paper Series (1999)
      Some road-pricing demonstrations use an approach called "value pricing", in which travelers can choose between a free but congested roadway and a priced roadway. Recent research has uncovered a potentially serious problem for such demonstrations: in certain models, second-best tolls are far lower than those typically charged, and the welfare gains from profit maximization are small or even negative. That research, however, assumes that all travelers are identical and it therefore neglects the benefits of product differentiation, by which people with different values of time can choose a suitable cost/quality combination. Using a model with two user groups, we find that accounting for heterogeneity in value of time is important in evaluating constrained policies, and improves the relative performance of policies that offer differential prices. Nevertheless, for most of the reasonable range of heterogeneity, second-best pricing produces far fewer benefits than pricing both roadways optimally, and profit-maximizing tolls are so high that overall welfare is reduced from the no-toll baseline.
        Cover page: The Value of "Value Pricing" of Roads: Second-Best Pricing and Product Differentiation
        • Article
        Working Paper Series (2002)
        Recent econometric advances have made it possible to empirically identify the varied nature of consumers' preferences. We apply these advances to study commuters' preferences for speedy and reliable highway travel with the objective of exploring the efficiency and distributional effects of road pricing that accounts for users' heterogeneity. Our analysis combines revealed and stated commuter choices of whether to pay a toll for congestion-free express travel or to travel free on regular congested roads. We find that highway users exhibit substantial heterogeneity in their values of travel time and reliability. Moreover, we show that road pricing policies that cater to varying preferences can substantially increase efficiency while maintaining the political feasibility exhibited by current experiments. By recognizing heterogeneity, policymakers may break the current impasse in efforts to relieve highway congestion.
          Cover page: Uncovering the Distribution of Motorists' Preferences for Travel Time and Reliability: Implications for Road Pricing
          • Article
          Earlier Faculty Research (2002)

          Recent econometric advances have made it possible to empirically identify the varied nature of consumers' preferences. We apply these advances to study commuters' preferences for speedy and reliable highway travel with the objective of exploring efficiency and distributional effects of road pricing that accounts for users' heterogeneity. Our analysis combines revealed and stated commuter choices of whether to pay a toll for congestion-free express travel or to travel free on regular congested roads. We find that highway users exhibit substantial heterogeneity in their values of travel time and reliability. Moreover, we show that road pricing policies that cater to varying preferences can substantially increase efficiency while maintaining the political feasibility exhibited by current experiments. By recognizing heterogeneity, policymakers may break the current impasse in efforts to relieve highway congestion.

            Cover page: Uncovering the Distribution of Motorists' Preferences for Travel Time and Reliability: Implications for Road Pricing
            • Article
            • Peer Reviewed
            UC San Francisco Previously Published Works (2023)
            Microbial community function depends on both taxonomic composition and spatial organization. While composition of the human gut microbiome has been deeply characterized, less is known about the organization of microbes between regions such as lumen and mucosa and the microbial genes regulating this organization. Using a defined 117 strain community for which we generate high-quality genome assemblies, we model mucosa/lumen organization with in vitro cultures incorporating mucin hydrogel carriers as surfaces for bacterial attachment. Metagenomic tracking of carrier cultures reveals increased diversity and strain-specific spatial organization, with distinct strains enriched on carriers versus liquid supernatant, mirroring mucosa/lumen enrichment in vivo. A comprehensive search for microbial genes associated with this spatial organization identifies candidates with known adhesion-related functions, as well as novel links. These findings demonstrate that carrier cultures of defined communities effectively recapitulate fundamental aspects of gut spatial organization, enabling identification of key microbial strains and genes.
              Cover page: Culturing of a complex gut microbial community in mucin-hydrogel carriers reveals strain- and gene-associated spatial organization.
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2020)
              Work function-mediated charge transfer in graphene/$\alpha$-RuCl$_3$ heterostructures has been proposed as a strategy for generating highly-doped 2D interfaces. In this geometry, graphene should become sufficiently doped to host surface and edge plasmon-polaritons (SPPs and EPPs, respectively). Characterization of the SPP and EPP behavior as a function of frequency and temperature can be used to simultaneously probe the magnitude of interlayer charge transfer while extracting the optical response of the interfacial doped $\alpha$-RuCl$_3$. We accomplish this using scanning near-field optical microscopy (SNOM) in conjunction with first-principles DFT calculations. This reveals massive interlayer charge transfer (2.7 $\times$ 10$^{13}$ cm$^{-2}$) and enhanced optical conductivity in $\alpha$-RuCl$_3$ as a result of significant electron doping. Our results provide a general strategy for generating highly-doped plasmonic interfaces in the 2D limit in a scanning probe-accessible geometry without need of an electrostatic gate.
                Cover page: Charge-Transfer Plasmon Polaritons at Graphene/alpha-RuCl3 Interfaces
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2020)
                Nanoscale charge control is a key enabling technology in plasmonics, electronic band structure engineering, and the topology of two-dimensional materials. By exploiting the large electron affinity of α-RuCl3, we are able to visualize and quantify massive charge transfer at graphene/α-RuCl3 interfaces through generation of charge-transfer plasmon polaritons (CPPs). We performed nanoimaging experiments on graphene/α-RuCl3 at both ambient and cryogenic temperatures and discovered robust plasmonic features in otherwise ungated and undoped structures. The CPP wavelength evaluated through several distinct imaging modalities offers a high-fidelity measure of the Fermi energy of the graphene layer: EF = 0.6 eV (n = 2.7 × 1013 cm-2). Our first-principles calculations link the plasmonic response to the work function difference between graphene and α-RuCl3 giving rise to CPPs. Our results provide a novel general strategy for generating nanometer-scale plasmonic interfaces without resorting to external contacts or chemical doping.
                  Cover page: Charge-Transfer Plasmon Polaritons at Graphene/α-RuCl3 InterfacesCreative Commons 'BY' version 4.0 license
                  • Article
                  • Peer Reviewed
                  UC San Francisco Previously Published Works (2022)
                  Molecular characterization of cell types using single-cell transcriptome sequencing is revolutionizing cell biology and enabling new insights into the physiology of human organs. We created a human reference atlas comprising nearly 500,000 cells from 24 different tissues and organs, many from the same donor. This atlas enabled molecular characterization of more than 400 cell types, their distribution across tissues, and tissue-specific variation in gene expression. Using multiple tissues from a single donor enabled identification of the clonal distribution of T cells between tissues, identification of the tissue-specific mutation rate in B cells, and analysis of the cell cycle state and proliferative potential of shared cell types across tissues. Cell type-specific RNA splicing was discovered and analyzed across tissues within an individual.
                    Cover page: The Tabula Sapiens: A multiple-organ, single-cell transcriptomic atlas of humans
                    • Article
                    • Peer Reviewed
                    UCLA Previously Published Works (2022)
                    Cell-free RNA from liquid biopsies can be analyzed to determine disease tissue of origin. We extend this concept to identify cell types of origin using the Tabula Sapiens transcriptomic cell atlas as well as individual tissue transcriptomic cell atlases in combination with the Human Protein Atlas RNA consensus dataset. We define cell type signature scores, which allow the inference of cell types that contribute to cell-free RNA for a variety of diseases.
                      Cover page: Cell types of origin of the cell-free transcriptome
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