Arena

Newsletter of the Boston University School of Medicine, Student American Medical Association (SAMA

Arena

Newsletter of the Boston University School of Medicine, Student American Medical Association (SAMA

Spacetime: Arena or Reality?

For small values of the mass (in relation to the angular momentum and electric charge), the Kerr-Newman (KN) solution of Einstein equation reduces to a naked singularity of circular shape. By considering the Hawking and Ellis extended interpretation of the KN spacetime, as well as Wheeler's idea of "charge without charge", the non-trivial topological structure of the extended KN spatial section is found to represent gravitational states with half-integral angular momentum. As a consequence, it can be consistently interpreted as a model for the electron-positron system, in which the concepts of mass, charge and spin emerge from the spacetime geometry. According to this model, therefore, instead of a simple arena, spacetime must have a concrete existence, being responsible -- through its highly non-trivial topological structures -- for the building blocks of (at least some of) the existing matter in the universe.Comment: Chapter in the book "Relativity and the Dimensionality of the World", Springer series "Fundamental Theories of Physics", Vol. 153 (2007). Volume Editor: Vesselin Petko

Libertas и политические отношения в поздней Римской республике

Данная монография предлагает сравнительный анализ идеи о libertas и ее практического воплощения в политической борьбе периода поздней Римской республики. Реконструируя представление римлян о libertas на фоне аналогичных концептов в классическую и эллинистическую эпохи, автор старается переосмыслить сущность политической борьбы в поздней Римской республике и ту роль, которую играло представление римлян о libertas в тогдашних политических отношениях.Монография включает указатель источников (c. 312-318) и общий указатель (c. 319-324)

The Non-Monetary Value of Reparations Rhetoric

I have several comments to offer on the subject of reparations. Reparations is not a single idea. The forty acres and a mule that General Sherman promised to the slaves was the beginning of the idea of reparations in America, but not the end. Reparations is a multi-part idea; until we get that straight, we are vulnerable to the feeling that we are lost again. There are at least three arenas in which the reparations issue may be contested. One is the political arena. In the arena of legislation and political maneuvering, bills must be submitted for majoritarian acceptance. It is no surprise that the current reparations bill has not gained the majority acceptance necessary for success. Thus, success in the political arena requires personal and collective political activism. The second arena is legal. In this arena those wronged can bring lawsuits. There is a coalition currently working on these lawsuits. As a lawyer, I must confess that the legal arena is probably less promising than the political arena. Although several legal precedents serve as barriers standing in the way of success in the courts, lawsuits are not, however, without value. One must simply understand their limited value. Lawsuits create the platform for the third, most important and powerful arena: the intellectual challenge to the history of racism. This arena allows us to challenge, to document, to read alternative stories, and to give those stories to our children-stories that help reposition Blacks from economic parasites to economic contributors unfairly deprived of their wealth. The intellectual arena provides an important strategic difference. When we address tired debates such as whether affirmative action is reverse discrimination, a different perspective emerges; reparations offers that positioning. Reparations as an intellectual project is most promising because it engages us all and gives us an opportunity to challenge the idea of racism - to challenge it as an idea that governs the way goods are distributed in society

Characterisation of global flow and local fluctuations in 3D SPH simulations of protoplanetary discs

A complete and detailed knowledge of the structure of the gaseous component in protoplanetary discs is essential to the study of dust evolution during the early phases of pre-planetesimal formation. The aim of this paper is to determine if three-dimensional accretion discs simulated by the Smoothed Particle Hydrodynamics (SPH) method can reproduce the observational data now available and the expected turbulent nature of protoplanetary discs. The investigation is carried out by setting up a suite of diagnostic tools specifically designed to characterise both the global flow and the fluctuations of the gaseous disc. The main result concerns the role of the artificial viscosity implementation in the SPH method: in addition to the already known ability of SPH artificial viscosity to mimic a physical-like viscosity under specific conditions, we show how the same artificial viscosity prescription behaves like an implicit turbulence model. In fact, we identify a threshold for the parameters in the standard artificial viscosity above which SPH disc models present a cascade in the power spectrum of velocity fluctuations, turbulent diffusion and a mass accretion rate of the same order of magnitude as measured in observations. Furthermore, the turbulence properties observed locally in SPH disc models are accompanied by meridional circulation in the global flow of the gas, proving that the two mechanisms can coexist.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society. 21 pages, 25 figure