Trends in Black-White Test-Score Differentials

Until the 1970s, there were few signs of change in the historic difference of one standard deviation between average ability or achievement test scores of blacks and whites in the United States. From about 1970 to the mid- to late 1980s, there was a substantial convergence of the average achievement test scores of black and white youth; however, from the mid- to late 1980s to 1992, test scores began to diverge again. Although we place the greatest weight on data from the National Assessment of Educational Progress (NAEP), the convergence also appeared in other test series. Herrnstein and Murray's highly visible work, The Bell Curve, stands almost alone in minimizing the importance of the convergent trend. We also find a longer-term trend of convergence between the verbal abilities of blacks and whites in data from the General Social Survey (GSS), which covers adult cohorts born since 1909.

Further Developments in Process Mapping and Modelling in Direct Metal Selective Laser Melting

This paper advances previous reported work on the mapping and modelling of single tracks and layers produced in powder beds of tool steel and stainless steel powders by a CO2 laser. For single tracks it reports on predicted and simulated track masses. It validates the simulations, including the use of absorption close to 1.0 when cylindrical tracks are formed. It also reports on melt pool temperature calculations and estimated melt pool dimensions which are used, in conjunction with bed physical properties, to explain why the single tracks form as either continuous with a crescent shape cross-section, continuous with an elliptical section, discontinuously irregularly broken, discontinuously balled or only partially melted as scan speeds and laser powers change. It then extends its scope, experimentally, to consider effects of scan spacing on single layer formation.Mechanical Engineerin

Maximal multihomogeneity of algebraic hypersurface singularities

From the degree zero part of logarithmic vector fields along an algebraic hypersurface singularity we indentify the maximal multihomogeneity of a defining equation in form of a maximal algebraic torus in the embedded automorphism group. We show that all such maximal tori are conjugate and in one-to-one correspondence to maxmimal tori in the degree zero jet of the embedded automorphism group. The result is motivated by Kyoji Saito's characterization of quasihomogeneity for isolated hypersurface singularities and extends its formal version and a result of Hauser and Mueller.Comment: 5 page

Encoding algebraic power series

Algebraic power series are formal power series which satisfy a univariate polynomial equation over the polynomial ring in n variables. This relation determines the series only up to conjugacy. Via the Artin-Mazur theorem and the implicit function theorem it is possible to describe algebraic series completely by a vector of polynomials in n+p variables. This vector will be the code of the series. In the paper, it is then shown how to manipulate algebraic series through their code. In particular, the Weierstrass division and the Grauert-Hironaka-Galligo division will be performed on the level of codes, thus providing a finite algorithm to compute the quotients and the remainder of the division.Comment: 35 page

The WTO Dispute Settlement System: A First Assessment from an Economic Perspective

We explore the incentives countries face in trade litigation within the new WTO Dispute Settlement System. Our analysis yields a number of interesting predictions. First, because sanctions are ruled out during the litigation process, the Dispute Settlement System does not preclude all new trade restrictions. However, the agendasetting capacity of the complainant, including its right to force a decision, make trade restrictions less attractive than under the WTO's predecessor GATT. Second, the system's appellate review provides the losing defendant with strong incentives to delay negative findings, and both parties with a possibility to signal their determinacy in fighting the case. Third, a relatively weak implementation procedure potentially reinforces incentives to violate WTO trade rules. Fourth, bilateral settlements are more likely at an early stage in the process and are biased towards the expected outcome of the formal dispute settlement procedure. Empirical evidence based on a first data set of cases at an advanced stage of the litigation process provides qualitative support for our claims.World trade organization;dispute settlement;trade restrictions

No New Symmetries of the Vacuum Einstein Equations

In this note we examine some recently proposed solutions of the linearized vacuum Einstein equations. We show that such solutions are {\it not} symmetries of the Einstein equations, because of a crucial integrability condition.Comment: 9 pages, Te

1.0 Mm Maps and Radial Density Distributions of Southern Hii/molecular Cloud Complexes

Several 1.0 continuum mapping observations were made of seven southern hemisphere h12/molecular cloud complexes with 65 arcsec resolution. The radial density distribution of the clouds with central luminosity sources was determined observationally. Strong similarities in morphology and general physical conditions were found to exist among all of the southern clouds in the sample

Telescopic actions

A group action H on X is called "telescopic" if for any finitely presented group G, there exists a subgroup H' in H such that G is isomorphic to the fundamental group of X/H'. We construct examples of telescopic actions on some CAT[-1] spaces, in particular on 3 and 4-dimensional hyperbolic spaces. As applications we give new proofs of the following statements: (1) Aitchison's theorem: Every finitely presented group G can appear as the fundamental group of M/J, where M is a compact 3-manifold and J is an involution which has only isolated fixed points; (2) Taubes' theorem: Every finitely presented group G can appear as the fundamental group of a compact complex 3-manifold.Comment: +higher dimension