Morphometric analysis of the postnatal development of the pig lung, with emphasis on alveoli and vessels, shows features of growth similar to man, but occurring at a much faster rate in the pig, which telescopes in the first 3 mo the changes seen in human childhood and adolescence. During the first weeks, arteries (birth to 2 wk) and alveoli (1--12 wk) increase in number, whereas increase in size continues until adulthood. Wall thickness decreases soon after birth in arteries 15--200 micrometer, and by 8 wk in those 200-1,000 micrometer. At this age the adult left ventricular predominance in weight is already present. Throughout growth the venous wall thickness does not change. Cardiopulmonary function studies in pigs, from 2 to 16 wk, show that, during the period of rapid postnatal lung growth, there is no change in tidal volume, dynamic compliance, and thoracic gas volume as related to body weight; right ventricular and pulmonary arterial pressures also remain unchanged, whereas pulmonary vascular resistance decreases during the 1st mo.
Although the U.S. economy 01 the early twenty-first century is vastly different from the US. economy prior to the 1970s: the nature of these economic changes and their impact on US. workers is unclear. This article claims that despite contemporary economic shifts. differential labor and employer power continues to segment the economy, and workers' position in the labor market continues to predict their rewards. beyond the effects of gender, race, and human capital. Drawing on segmented labor market and dual economy research, we propose a four-category model of the structural factors that influence variance in work-relatcd rewards. We examine the distribution of jobs in each of four categories betwecn 1974 and 2000 and observe that losses and gains across categories are unevenly distributcd by race and gender. While white men have experienced the greatest dcclincs in employment and earnings, they have maintained their absolute advantage over women and nonwhites. In multivariate analyses, we fmd that the structural position of employmcnt continues to be a significant determinant of wages. Although women and racial minorities have expcrienced sizable increases in employment in primary labor market jobs in the core of the economy. both groups remain overrepresented in low-paying jobs. Moreover women, but not nonwhite men. consistently receive significantly fewer rewards for their labor in both low-paying and high-paying jobs. Our findings suggest that structural factors continue to influence earnings inequality, cspecially across race and gender lines.It is virtually irrefutable that the U.S. economy has changed dramatically over the past thirty years, as the foundation of the country's economic infrastructure has shifted from a bureaucratic, industrial economy characterized by relative production and employment stability to a postbureaucratic, mixed economy characterized by flexibility Direct correspondence to
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