Engines of Growth: Farm Tractors and Twentieth-Century U.S. Economic Welfare

The role of twentieth-century agricultural mechanization in changing the productivity, employment opportunities, and appearance of rural America has long been appreciated. Less attention has been paid to the impact made by farm tractors, combines, and associated equipment on the standard of living of the U.S. population as a whole. This paper demonstrates, through use of a detailed counterfactual analysis, that mechanization in the production of farm products increased GDP by more than 8.0 percent, using 1954 as a base year. This result suggests that studying individual innovations can significantly increase our understanding of the nature of economic growth.

Hubble Advanced Camera for Surveys Observations of the z=6.42 Quasar SDSS 1148+5251: A Leak in the Gunn-Peterson Trough

The Hubble Advanced Camera for Surveys has been used to obtain a narrow-band image of the weak emission peak seen at lambda=7205 A in the Gunn-Peterson Ly beta absorption trough of the highest redshift quasar, SDSS J1148+5251. The emission looks perfectly point-like; there is no evidence for the intervening galaxy that we previously suggested might be contaminating the quasar spectrum. We derive a more accurate astrometric position for the quasar in the two filters and see no indication of gravitational lensing. We conclude that the light in the Ly beta trough is leaking through two unusually transparent, overlapping windows in the IGM absorption, one in the Ly beta forest at z ~ 6 and one in the Ly alpha forest at z ~ 5. If there are significant optical depth variations on velocity scales small compared with our spectral resolution (~150 km/s), the Ly alpha trough becomes more transparent for a given Ly beta optical depth. Such variations can only strengthen our conclusion that the fraction of neutral hydrogen in the IGM increases dramatically at z>6. We argue that the transmission in the Ly beta trough is not only a more sensitive measure of the neutral fraction than is Ly alpha, it also provides a less biased estimator of the neutral hydrogen fraction than does the Ly alpha transmission.Comment: Submitted to the Astronomical Journa

Flexible correction processes in social judgment: implications for persuasion

Journal ArticleTwo experiments were conducted to examine correction for perceived bias in persuasion situations. Study 1 showed that, although a manipulation of source likability had an impact on attitudes when no instruction to remove bias was present, when people were asked to remove any bias from their judgments, the effect of the source likability manipulation disappeared. The fact that the correction instruction did not increase the impact of an argument quality manipulation on attitudes suggested that effort aimed at correction is conceptually distinct from effort aimed at processing a message in general. Study 2 showed that a correction for source likability took place under low elaboration conditions--where a manipulation of source likability had an impact when no correction instructions were provided, and under high elaboration conditions--where a manipulation of source likability had no impact when no correction instructions were provided. In the high elaboration conditions, correcting for an impact that was not actually present led a dislikable source to be more influential than a likable source

An FeLoBAL Binary Quasar

In an ongoing infrared imaging survey of quasars at Keck Observatory, we have discovered that the z=1.285 quasar SDSS J233646.2-010732.6 comprises two point sources with a separation of 1.67". Resolved spectra show that one component is a standard quasar with a blue continuum and broad emission lines; the other is a broad absorption line (BAL) quasar, specifically, a BAL QSO with prominent absorption from MgII and metastable FeII, making it a member of the ``FeLoBAL'' class. The number of known FeLoBALs has recently grown dramatically from a single example to more than a dozen, including a gravitationally lensed example and the binary member presented here, suggesting that this formerly rare object may be fairly common. Additionally, the presence of this BAL quasar in a relatively small separation binary adds to the growing evidence that the BAL phenomenon is not due to viewing a normal quasar at a specific orientation, but rather that it is an evolutionary phase in the life of many, if not all, quasars, and is particularly associated with conditions found in interacting systems.Comment: AASTEX 13 pp., 4 figs; accepted by ApJ Letter