The Discovery of Sgr A*

The compact radio source Sgr A* is associated with a 3.6 million black hole at the center of the Milky Way. The radio source was discovered in February 1974 by Bruce Balick and Robert L.Brown. The National Radio Astronomy Observatory's Green Bank 35 km radio link interferometer was used. We discuss other observations in the years 1965-1985 as well as early VLBI observations. The name Sgr A* was used for the first time in 1982 by Robert L.Brown and has become the accepted name in the intervening years.Comment: 8 pages,2 figures. Conference proceedings: "The central 300 parsecs of the Milky Way", editors A.Cotera, H.Falcke, T.R.Geballe, S.Markof

Afterthoughts | Complexities of Potency

Afterthoughts to themed perspectives on Complexities of Potency

Moduli of PT-semistable objects II

We generalise the techniques of semistable reduction for flat families of sheaves to the setting of the derived category $D^b(X)$ of coherent sheaves on a smooth projective three-fold $X$. Then we construct the moduli of PT-semistable objects in $D^b(X)$ as an Artin stack of finite type that is universally closed. In the absence of strictly semistable objects, we construct the moduli as a proper algebraic space of finite type.Comment: 34 pages. Exposition improved based on referee's comments, especially the proofs of Prop 2.6 and 2.17 (of this version). References added; typos corrected. Openness and separatedness now in a separate section. Sections 4 and 5 of previous version removed. Accepted for publication by the Transactions of the American Mathematical Society. This is the sequel to http://arxiv.org/abs/1011.568

Assessing the Role of Foreign Direct Investment in China’s Economic Development: Macro Indicators and Insights from Sectoral-Regional Analyses

The objective of this paper is to assess the role of FDI in China’s economic development with reference to the broader literature on FDI and late development. Three main findings come out from the analyses in the paper. First, it is found that FDI tends to promote the improvement in allocative efficiency, while having a negative impact on productive efficiency. Second, insofar as FDI does promote overall productivity growth, this tends to be a matter of cumulative causation rather than one of single-direction causation. Third, in the context of a comparative analysis of two distinctive regional models, it is found that the economic impact of FDI tends to be more favourable in the inward-looking, capital-deepening pattern of development (the ‘Shanghai model’) than that in the export-oriented, labour-intensive pattern (the ‘Guangdong model’). Further analyses, however, suggest that the ‘Shanghai model’ has its intrinsic problems of sustainability. The scope for applying it to China as a whole is thus judged to be limited

A relation between higher-rank PT stable objects and quotients of coherent sheaves

On a smooth projective threefold, we construct an essentially surjective functor $\mathcal{F}$ from a category of two-term complexes to a category of quotients of coherent sheaves, and describe the fibers of this functor. Under a coprime assumption on rank and degree, the domain of $\mathcal{F}$ coincides with the category of higher-rank PT stable objects, which appear on one side of Toda's higher-rank DT/PT correspondence formula. The codomain of $\mathcal{F}$ is the category of objects that appear on one side of another correspondence formula by Gholampour-Kool, between the generating series of topological Euler characteristics of two types of quot schemes.Comment: 19 page