5,493 research outputs found
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
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