This paper uses information from the Dictionary of Occupational Titles (DOT) and Displaced Worker Surveys (DWS) to provide evidence on the source of human capital specificity. Measures of four basic skills are constructed from the detailed DOT information. These measures are used to characterize the skill portfolio of each job and to construct distance measures between jobs.The pattern of wage losses from the DWS shows that large losses are more closely associated with switching skill portfolios than switching industry or occupation code per se and that these switches represent large decreases in the underlying skill portfolio in the post-displacement job. The recent evidence for industry specific capital is re-examined. An analysis using the same methods as Neal (1995) that incorporates the skill portfolio measures provides further evidence in favor of broad skill based specificity.2

Separate identification of the price and quantity of human capital has important implications for understanding key issues in labor economics and macroeconomics. Price and quantity series are derived and subjected to robustness checks. The human capital price series associated with different education levels are highly correlated and exhibit a strong secular trend. Three resulting implications are explored: (1) using the derived quantities life-cycle profiles are re-examined; (2) the rising college premium is reinterpreted and found to be mainly driven by relative quantity changes, and (3) adjusting the labor input for quality increases dramatically reduces the contribution of MFP to growth. * The authors wish to thank Lance Lochner and Todd Stinebrickner for helpful comments and discussion.

Selective laser melting involves melting and solidification of metal powder particles in a track-by-track and layer-by-layer method to fabricate 3D parts. The present investigation focuses on understanding the effect of laser power and scan speed on the evolution of melt pool, porosity and multiple thermal cycling effects on the microstructure in parts fabricated using selective laser melting. In this study, Ti-6Al-4V pre-alloyed powder was used to produce single-track deposits and bulk parts. Using different combinations of laser power and scan speeds, single-track deposits and bulk parts were produced. The cross-sections of the single-track deposits and bulk samples were prepared for metallographic observations and the melt pool shape and size and porosity were evaluated. When a low energy density was applied the un-melted powder particles produced irregularly shaped porosity, and a high energy density resulted in rounded porosity, which was due to keyhole effects. The samples produced with a proper combination of power and speeds were fully dense. Further, microstructural development under the influence of process condition was highlighted. Overall, the study demonstrates a good correlation between the single-track melt pool geometries, porosity in bulk parts and also demonstrates the microstructural inhomogeneity during deposition.

Recent immigration appears to be characterized by frequent return and onward migration. This has important consequences for the contribution of immigrants to the economy of the host country. Lack of longitudinal data has prevented much analysis of whether recent international migration is more like internal migration and not a once-for-all move with a possible return should the move prove to have been a mistake. A newly available longitudinal data set covering all immigrants to Canada since 1980 provides the opportunity to address the issues raised by the new migration. The results show that a large fraction of male immigrants who are working age, especially among skilled workers and entrepreneurs, are highly internationally mobile.

This paper studies the effects of unions on the structure of wages, using an estimation technique that explicitly accounts for misclassification errors in reported union status, and potential correlations between union status and unobserved productivity. The econometric model is estimated separately for five skill groups using a large panel data set formed from the U.S. Current Population Survey. The results suggest that unions raise wages more for workers with lower levels of observed skills. In addition, the patterns of selection bias differ by skill group. Among workers with lower levels of observed skill, unionized workers are positively selected, whereas union workers are negatively selected from among those with higher levels of observed skill. KEYWORDS:Longitudinal data, unobserved heterogeneity, measurement error, trade unions. 'Originally prepared for the 1991 Conference of the Econometric Study Group in Bristol, England. I am grateful to Michael Quinn for outstanding research assistance, and to Gary Solon for pointing out an error in an earlier draft. Thanks to Orley Ashenfelter, Henry Farber, Alan Krueger, the editor and two referees for comments. 'See Robinson (1989) for a discussion of these approaches and a comparison of the underlying assumptions typically used in each.