Recent Results from Infrared Observations of White Dwarfs, their Companions, and the Dust that Surrounds Them

Although "traditionally" observed at short wavelengths, white dwarfs have displayed many surprising features when probed in the infrared. We present an overview of recent results from ground- and space-based near- to mid-infrared observations of white dwarfs. These include the discovery of many new candidate binary stars containing low mass stellar or sub-stellar companions from a sample of objects previously thought to be single white dwarfs, and Spitzer Space Telescope observations that suggest that dust is common in the environs of white dwarfs in cataclysmic variables

Agent Causation: Before and After the Ontological Turn

Imagine Ludwig has a cup of tea for breakfast. He\ud pours it; he eats his egg until it seems to him that the tea\ud should have the right temperature; he moves his hand to\ud the cup, puts his fingers at the handle, and then, careful\ud not to spill anything, he does something with his arm;\ud namely, he raises it, and if all goes well he then drinks the\ud tea without burning his lips.\ud The rising of Ludwig"s arm surely has a cause. But\ud what is the cause? Defenders of agent causation, such as\ud Thomas Reid (1788), Richard Taylor (1966), Roderick\ud Chisholm (1976a), and many more recent authors (see\ud Swinburne 1997, ch. 5; Thorp 1980; Meixner 1999; Clarke\ud 1996; O'Connor 2000) have argued that the rising of\ud Ludwig"s arm is caused by Ludwig himself. Some events\ud are caused, not by other events, but by concrete things, by\ud substances, more specifically by intentional agents

Operator Representations on Quantum Spaces

In this article we present explicit formulae for q-differentiation on quantum spaces which could be of particular importance in physics, i.e., q-deformed Minkowski space and q-deformed Euclidean space in three or four dimensions. The calculations are based on the covariant differential calculus of these quantum spaces. Furthermore, our formulae can be regarded as a generalization of Jackson's q-derivative to three and four dimensions.Comment: 34 pages, Latex, major modifications to improve clarity, corrected typo

Green investment strategies: a positive force in cities

Deterioration of urban neighborhoods is known to induce out migration, but how well do public investments to reverse decline actually work? To evaluate Philadelphia’s greening investment, researchers measured property buyers’ willingness to pay more—and found that greening works.Community development