Relativistic Accretion

A brief summary of the properties of astrophysical black holes is presented. Various modes of accretion are distinguished, corresponding to accretion at rates from well below to well above the Eddington rate. The importance of mass loss is emphasized when the accreting gas cannot radiate and it is asserted that a strong wind is likely to be necessary to carry off mass, angular momentum and energy from the accreting gas. The possible importance of the black hole spin in the formation of jets and in dictating the relative importance of non-thermal emission over thermal radiation is discussed.Comment: To appear in "Astrophysical Discs", ASP Conference Series, 13 pages, latex, 0 figure

Coping with unpleasant surprises in a complex world: Is rational choice possible in a world with positive information costs?

This paper provides a rational choice-based analysis of the causes and consequences of surprise events. The paper argues that ignorance may be rational, but nonetheless produce systematic mistakes, inconsistent behavior, and both pleasant and unpleasant surprises. If ignorance and unpleasant surprises are commonplace and relevant for individual and group decisionmaking, we should observe standing institutions for dealing with them - and we do. Insofar as surprises are consistent with rational choice models, but left outside most models, it can be argued that these methodological choices mistakenly limit the scope of rational choicebased research. --Ignorance,Rational Ignorance,Natural Ignorance,Bounded Rationality,Rational Choice,Biased Expectations,Crisis Management,Social Insurance,Bailouts,Economics of Information

First row transition metal catalysts for solar-driven water oxidation produced by electrodeposition

As our reliance on renewable energy resources increases, so will our need to store this energy in the form of chemical fuels to iron-out peaks and troughs in supply. Sunlight, the most plentiful source of renewable energy, is especially problematic in this regard as it is so diffuse. One way to convert solar irradiation to fuels effectively would be to develop large surface area photo-electrochemical devices that could use sunlight directly to split water into H2 and O2. However, in order to be feasible, such an approach requires that these devices (and their components) are extremely cheap. In this review, we will discuss catalysts for the water oxidation half-reaction of electrochemical water splitting that can be produced by electrodeposition (a technique well suited to large-scale, low-cost applications), and that are based on the comparatively plentiful and inexpensive first row transition metals. Special attention will be paid to the electrodeposition conditions used in the various examples given, and structure-function relationships for electrochemical water oxidation for the materials produced by these techniques will be elucidated

Run Time Approximation of Non-blocking Service Rates for Streaming Systems

Stream processing is a compute paradigm that promises safe and efficient parallelism. Modern big-data problems are often well suited for stream processing's throughput-oriented nature. Realization of efficient stream processing requires monitoring and optimization of multiple communications links. Most techniques to optimize these links use queueing network models or network flow models, which require some idea of the actual execution rate of each independent compute kernel within the system. What we want to know is how fast can each kernel process data independent of other communicating kernels. This is known as the "service rate" of the kernel within the queueing literature. Current approaches to divining service rates are static. Modern workloads, however, are often dynamic. Shared cloud systems also present applications with highly dynamic execution environments (multiple users, hardware migration, etc.). It is therefore desirable to continuously re-tune an application during run time (online) in response to changing conditions. Our approach enables online service rate monitoring under most conditions, obviating the need for reliance on steady state predictions for what are probably non-steady state phenomena. First, some of the difficulties associated with online service rate determination are examined. Second, the algorithm to approximate the online non-blocking service rate is described. Lastly, the algorithm is implemented within the open source RaftLib framework for validation using a simple microbenchmark as well as two full streaming applications.Comment: technical repor