Showing 411 - 420 of 2039 Items
The Impact of Ride-Hailing Services on Public Transportation Use: A Discontinuity Regression Analysis
Date: 2017-05-26
Creator: Nicole Sadowsky
Erik Nelson
Access: Open access
- Since 2011, the private ride-hailing companies Uber and Lyft have expanded into more and more US cities. We use regression discontinuity design to examine the impact of Uber and Lyft’s entry on public transportation use in the US’ largest urban areas. In most cases, entry into cities by the two ride-hailing companies was staggered: Uber entered first followed some months later by Lyft. We find that public transportation use increased in an urban area, all else equal, immediately following the first entry. However, we find that the spike in public transportation use after first entry disappeared following the entry of the second company. In fact there is some evidence that monthly public transportation ridership levels fell below their pre-first entry levels. In other words, the joint presence of the two major private ride-hailing services transformed ride-hailing services from a public transportation complement to a public transportation substitute, at least in the studied urban areas. We speculate that the first entrant complemented public transportation use for some in an urban area by solving the “last-mile” problem and by providing a potentially safer option at night when public transportation service has been reduced. However, we speculate the second entrant is likely to have spurred price competition in the urban area’s ride-hailing duopoly market and an increase in ride-hailing car supply. This competitive effect could have tipped the scales, making an entire trip with a ride-hailing service more cost-effective and convenient than splitting a trip between a ride-share company and public transportation.
The distributional impact of a green payment policy for organic fruit
Date: 2019-02-01
Creator: Erik Nelson
John Fitzgerald
Nathan Tefft
Access: Open access
- Consumer spending on organic food products has grown rapidly. Some claim that organics have ecological, equity, and health advantages over conventional food and therefore should be subsidized. Here we explore the distributive impacts of an organic fruit subsidy that reduces the retail price of organic fruit in the US by 10 percent. We estimate the impact of the subsidy on organic fruit demand in a representative poor, middle income, and rich US household using three analytical methods; including two econometric and one machine learning. We do not find strong evidence of regressive redistribution due to our simulated organic fruit subsidy; the poor household’s relative reaction to the subsidy is not much different than the reaction at the other two households. However, the infra-marginal savings from the subsidy tend to be larger in richer households.
Analysis of the yeast arginine methyltransferase Hmt1p/Rmt1p and its in vivo function. Cofactor binding and substrate interactions
Date: 2000-02-04
Creator: Anne E. McBride
Valerie H. Weiss
Heidi K. Kim
James M. Hogle
Pamela A., Silver
Access: Open access
- Many eukaryotic RNA-binding proteins are modified by methylation of arginine residues. The yeast Saccharomyces cerevisiae contains one major arginine methyltransferase, Hmt1p/Rmt1p, which is not essential for normal cell growth. However, cells missing HMT1 and also bearing mutations in the mRNA-binding proteins Np13p or Cbp80p can no longer survive, providing genetic backgrounds in which to study Hmt1p function. We now demonstrate that the catalytically active form of Hmt1p is required for its activity in vivo. Amino acid changes in the putative Hmt1p S-adenosyl-L-methionine-binding site were generated and shown to be unable to catalyze methylation of Np13p in vitro and in vivo or to restore growth to strains that require HMT1. In addition these mutations affect nucleocytoplasmic transport of Np13p. A cold- sensitive mutant of Hmt1p was generated and showed reduced methylation of Np13p, but not of other substrates, at 14 °C. These results define new aspects of Hmt1 and reveal the importance of its activity in vivo.
Optical proxy for phytoplankton biomass in the absence of photophysiology: Rethinking the absorption line height
Date: 2013-01-01
Creator: Collin S. Roesler
Andrew H. Barnard
Access: Open access
- The pigment absorption peak in the red waveband observed in phytoplankton and particulate absorption spectra is primarily associated with chlorophyll-a and exhibits much lower pigment packaging compared to the blue peak. The minor contributions to the signature by accessory pigments can be largely removed by computing the line height absorption at 676 nm above a linear background between approximately 650 nm and 715 nm. The line height determination is also effective in removing the contributions to total or particulate absorption by colored dissolved organic matter and non-algal particles, and is relatively independent of the effects of biofouling. The line height absorption is shown to be significantly related to the extracted chlorophyll concentration over a large range of natural optical regimes and diverse phytoplankton cultures. Unlike the in situ fluorometric method for estimating chlorophyll, the absorption line height is not sensitive to incident irradiance, in particular non-photochemical quenching. The combination of the two methods provides a combination of robust phytoplankton biomass estimates, pigment based taxonomic information and a means to estimate the photosynthetic parameter, , the irradiance at which photosynthesis transitions from light limitation to light saturation. © 2013 The Authors. E K
Statement by Anonymous (Paula) collected by Erika Bjorum on October 5, 2018 [part 1]
Date: 2018-10-05
Creator: Anonymous (Paula)
Access: Open access
- Transcription of statement includes parts 1 and 2, recorded on October 5 and October 9, 2018. This statement was given privately.
Statement by Sarah Mary (Anne) McCarron collected by Rachel George on May 1, 2014
Date: 2014-05-01
Creator: Sarah Mary McCarron
Access: Open access
Statement by Sandra Pictou collected by Marcie Lister on October 16, 2014
Date: 2014-10-16
Creator: Sandra Pictou
Access: Open access
Homotypic and heterotypic continuity of fine-grained temperament during infancy, toddlerhood, and early childhood
Date: 2008-07-01
Creator: Samuel P. Putnam
Mary K. Rothbart
Maria A. Gartstein
Access: Open access
- Longitudinal continuity was investigated for fine-grained and factor-level aspects of temperament measured with the Infant Behaviour Questionnaire-Revised (IBQ-R), Early Childhood Behaviour Questionnaire (ECBQ), and Children's Behaviour Questionnaire (CBQ). Considerable homotypic continuity was found. Convergent and discriminant validity of the measures was supported, as all fine-grained dimensions exhibited stability across adjacent measurement periods, and all scales found on both the ECBQ and CBQ were most highly correlated with their equivalent scales. At the factor level, Surgency and Negative Affect factors were stable across all time points, and Effortful Control/Regulatory Capacity was stable across adjacent time periods. High-Intensity Pleasure, Activity Level, and Impulsivity contributed strongly to continuity of Surgency, and Sadness, Frustration, and Falling Reactivity played strong roles in the continuity of Negative Affect. Heterotypic continuity was also found. High levels of Infant Surgency predicted high toddler Effortful Control, whereas high toddler Surgency predicted low Effortful Control in preschoolers. Infant Surgency dimensions especially predicted Toddler Attention Shifting and Low-Intensity Pleasure, and toddler Activity Level was most closely associated with later deficits in Effortful Control. Inverse relations were also obtained between Negative Affect and Effortful Control, with substantial negative connections between toddler Negative Affect and preschool Attention Focusing and Inhibitory Control. Copyright © 2008 John Wiley & Sons, Ltd.
JUST A BIG MISUNDERSTANDING? BIAS AND BAYESIAN AFFECTIVE POLARIZATION
Date: 2020-02-01
Creator: Daniel F. Stone
Access: Open access
- I present a model of affective polarization—growth in hostility over time between two parties—via quasi-Bayesian inference. In the model, two agents repeatedly choose actions. Each choice is based on a balance of concerns for private interests and the social good. More weight is put on private interests when an agent's character is intrinsically more self-serving and when the other agent is believed to be more self-serving. Each agent Bayesian updates about the other's character, and dislikes the other more when she is perceived as more self-serving. I characterize the effects on growth in dislike of three biases: a prior bias against the other agent's character, the false consensus bias, and limited strategic thinking. Prior bias against the other's character remains constant or declines over time, and actions do not diverge. The other two biases cause actions to become more extreme over time and repeatedly be “worse” than expected, causing mutual growth in dislike, that is, affective polarization. The magnitude of dislike can become arbitrarily large—even when both players are arbitrarily “good” (unselfish). The results imply that seemingly irrelevant cognitive biases can be an important cause of the devolution of relationships, in politics and beyond, and that subtlety and unawareness of bias can be key factors driving the degree of polarization.
Wave transmission in time- and space-variant helicoidal phononic crystals
Date: 2014-11-04
Creator: F. Li
C. Chong
J. Yang
P. G. Kevrekidis
C., Daraio
Access: Open access
- We present a dynamically tunable mechanism of wave transmission in one-dimensional helicoidal phononic crystals in a shape similar to DNA structures. These helicoidal architectures allow slanted nonlinear contact among cylindrical constituents, and the relative torsional movements can dynamically tune the contact stiffness between neighboring cylinders. This results in cross-talking between in-plane torsional and out-of-plane longitudinal waves. We numerically demonstrate their versatile wave mixing and controllable dispersion behavior in both wavenumber and frequency domains. Based on this principle, a suggestion toward an acoustic configuration bearing parallels to a transistor is further proposed, in which longitudinal waves can be switched on and off through torsional waves.