The Nature of Hypervelocity Stars and the Time between Their Formation and Ejection

We obtain Keck HIRES spectroscopy of HVS5, one of the fastest unbound stars in the Milky Way halo. We show that HVS5 is a 3.62 ± 0.11 M_☉ main-sequence B star at a distance of 50 ± 5 kpc. The difference between its age and its flight time from the Galactic center is 105 ± 18 (stat) ±30 (sys) Myr; flight times from locations elsewhere in the Galactic disk are similar. This 10^8 yr "arrival time" between formation and ejection is difficult to reconcile with any ejection scenario involving massive stars that live for only 10^7 yr. For comparison, we derive arrival times of 10^7 yr for two unbound runaway B stars, consistent with their disk origin where ejection results from a supernova in a binary system or dynamical interactions between massive stars in a dense star cluster. For HVS5, ejection during the first 10^7 yr of its lifetime is ruled out at the 3σ level. Together with the 10^8 yr arrival times inferred for three other well-studied hypervelocity stars (HVSs), these results are consistent with a Galactic center origin for the HVSs. If the HVSs were indeed ejected by the central black hole, then the Galactic center was forming stars ≃200 Myr ago, and the progenitors of the HVSs took ≃100 Myr to enter the black hole's loss cone

Conditioning an additive functional of a markov chain to stay non-negative. I, Survival for a long time

Let (X-t)(t >= 0) be a continuous-time irreducible Markov chain on a finite state space E, let v be a map v: E -> R \ {0}, and let (phi(t))(t >= 0) be an additive functional defined by phi(t) = integral(0)(t)(X-s) ds. We consider the case in which the process (phi(t))(t >= 0) is oscillating and that in which (phi(t))(t >= 0) has a negative drift. In each of these cases, we condition the process (X-t, phi(t))(t >= 0) on the event that (phi(t))(t >= 0) is nonnegative until time T and prove weak convergence of the conditioned process as T -> infinity

The United States and Japan in the Postwar World

A major phenomenon in the post-World War II world is the rise of Japan as a leading international economic and industrial power. This advance began with American aid in rebuilding the nation after the war, but it has now seen Japan rival and even outstrip the United States on several fronts. The relations between the two powers and the impact that they have on economic and political factors during the postwar years are the focus of this important book. The editors, Akira Iriye and Warren I. Cohen, themselves noted authorities on Asian affairs, have gathered here contributions from a distinguished group of American and Japanese scholars. The resulting collection represents a unique blend of viewpoints from each side of the American-Japanese relationship. Akira Iriye is Charles Warren Professor of American History at Harvard University. Warren I. Cohen is Distinguished University Professor at the University of Maryland, Baltimore County. A rich volume that will be of interest not only to specialists, but also especially to government officials and the business and financial community. —History A useful guide to an understanding of the strains and stresses between the United States and Japan as the two countries move toward the end of the twentieth century. —Journal of American Historyhttps://uknowledge.uky.edu/upk_political_science_international_relations/1022/thumbnail.jp

The Meaning of the Changes within the Framework of Subchapter C and the Impact on Proposals for Integration of the Corporate and Individual Tax

Professor Cohen warns against an easy acceptance of repeal of General Utilities and other aspects of the Staff Proposal. He believes that the problem can be more fruitfully discussed in the context of an integrated form of tax, where double tax burdens are ameliorated. Professors Warren and Andrews discuss two proposals for restructuring the tax consequences of corporate distributions and the integration of the individual and corporate income taxes, as a means of eliminating double tax burdens and other inequities, and the American Law Institute Reporter\u27s Study

Some Properties of the Speciation Model for Food-Web Structure - Mechanisms for Degree Distributions and Intervality

We present a mathematical analysis of the speciation model for food-web structure, which had in previous work been shown to yield a good description of empirical data of food-web topology. The degree distributions of the network are derived. Properties of the speciation model are compared to those of other models that successfully describe empirical data. It is argued that the speciation model unifies the underlying ideas of previous theories. In particular, it offers a mechanistic explanation for the success of the niche model of Williams and Martinez and the frequent observation of intervality in empirical food webs.Comment: 23 pages, 6 figures, minor rewrite

Geographical Embedding of Scale-Free Networks

A method for embedding graphs in Euclidean space is suggested. The method connects nodes to their geographically closest neighbors and economizes on the total physical length of links. The topological and geometrical properties of scale-free networks embedded by the suggested algorithm are studied both analytically and through simulations. Our findings indicate dramatic changes in the embedded networks, in comparison to their off-lattice counterparts, and call into question the applicability of off-lattice scale-free models to realistic, everyday-life networks