Actinoid pnictides--I : Heat capacities from 5 to 950 K and magnetic transitions of U3As4 and U3Sb4. Ferromagnetic transitions

The heat capacities of triuranium tetraarsenide (U3As4) and triuranium tetraantimonide (U3Sb4), measured by adiabatic calorimetry over the temperature range 5-950 K, show sharp [lambda]-shaped transitions at 196.1 and 147.5 K, respectively. The maxima are related to the appearance of permanent magnetic moments below 198 and 148 K. Excess cooperative entropies associated with ferromagnetic ordering are tentatively estimated as 6.7 for U3As4 and 6.8 cal K-1 mole-1 for U3Sb4. These are larger than the two literature values reported for U3P4 (1.5 and 3.1 cal K-1 mole-1). The fact that these entropy of transition values are much smaller than would be expected from [Delta]St = R In (2J + 1) for the 3H4 ground term (J = 4) and that the observed heat capacities at high temperatures are much larger than would be expected from lattice plus dilational contributions are evidence of crystal field effects. The total electronic entropies to 950 K are estimated as 11.05 and 12.95 cal K-1 mole-1 for U3As4 and U3Sb4, respectively. Thermal functions for both U3As4 and U3Sb4 are integrated from the experimental data up to 950 K. At 298.15 K, the values of Cpo [So(T)-So(0)] and -{[Go(T)-Ho(0)]/T} in cal K-1 mole-1, are 44.82, 73.87 and 38.97, U3As4 and 44.98, 83.60 and 46.89, for U3Sb4.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23080/1/0000655.pd

The great reversal in the demand for skill and cognitive tasks

What explains the current low rate of employment in the US? While there has been substantial debate over this question in recent years, we believe that considerable added insight can be derived by focusing on changes in the labor market at the turn of the century. In particular, we argue that in about the year 2000, the demand for skill (or, more specifically, for cognitive tasks often associated with high educational skill) underwent a reversal. Many researchers have documented a strong, ongoing increase in the demand for skills in the decades leading up to 2000. In this paper, we document a decline in that demand in the years since 2000, even as the supply of high education workers continues to grow. We go on to show that, in response to this demand reversal, high-skilled workers have moved down the occupational ladder and have begun to perform jobs traditionally performed by lower-skilled workers. This de- skilling process, in turn, results in high-skilled workers pushing low-skilled workers even further down the occupational ladder and, to some degree, out of the labor force all together. In order to understand these patterns, we offer a simple extension to the standard skill biased technical change model that views cognitive tasks as a stock rather than a flow. We show how such a model can explain the reversal in the data that we present, and offers a novel interpretation of the current employment situation in the US