A new factorization property of the selfdecomposable probability measures

We prove that the convolution of a selfdecomposable distribution with its background driving law is again selfdecomposable if and only if the background driving law is s-selfdecomposable. We will refer to this as the factorization property of a selfdecomposable distribution; let L^f denote the set of all these distributions. The algebraic structure and various characterizations of L^f are studied. Some examples are discussed, the most interesting one being given by the Levy stochastic area integral. A nested family of subclasses L^f_n, n\ge 0, (or a filtration) of the class L^f is given.Comment: Published at http://dx.doi.org/10.1214/009117904000000225 in the Annals of Probability (http://www.imstat.org/aop/) by the Institute of Mathematical Statistics (http://www.imstat.org

Engineering prediction of turbulent skin friction and heat transfer in high-speed flow

A large collection of experimental turbulent-skin-friction and heat-transfer data for flat plates and cones was used to determine the most accurate of six of the most popular engineering-prediction methods; the data represent a Mach number range from 4 to 13 and ratio of wall to total temperature ranging from 0.1 to 0.7. The Spalding and Chi method incorporating virtual-origin concepts was found to be the best prediction method for Mach numbers less than 10; the limited experimental data for Mach numbers greater than 10 were not well predicted by any of the engineering methods except the Coles method

Turbulent skin friction and heat-transfer charts adapted from the Spalding and Chi method

Local and average skin friction and heat transfer on flat plates in air - chart

Onset of Collective Oscillation in Chemical Turbulence under Global Feedback

Preceding the complete suppression of chemical turbulence by means of global feedback, a different universal type of transition, which is characterized by the emergence of small-amplitude collective oscillation with strong turbulent background, is shown to occur at much weaker feedback intensity. We illustrate this fact numerically in combination with a phenomenological argument based on the complex Ginzburg-Landau equation with global feedback.Comment: 6 pages, 8 figures; to appear in Phys. Rev.

Real, virtual, and other personas in an online collaborative environment

This presentation reports on a study of an unusual online course, which incorporates collaboration across campuses in teaching about evaluation of information technologies. Issues raised by new information technologies are major foci within the course, and also entry points for our study of its implementation.published or submitted for publicationis peer reviewe

A Water Accounting System for Strategic Water Management

This paper describes a water accounting system (WAS) that has been developed as an innovative new tool for strategic long-term water management. The WAS incorporates both disaggregated water use and availability, provides a comprehensive and consistent historical database, and can integrate climate and hydrological model outputs for the exploration of scenarios. It has been established and tested for the state of Victoria in Australia, and can be extended to cover other or all regions of Australia. The WAS is implemented using stock-and-flow dynamics, currently employing major river basins as the spatial units and a yearly time step. While this system shares features with system dynamics, learning is enhanced and strategic management of water resources is improved by application of a Design Approach and the structure of the WAS. We compare the WAS with other relevant accounting systems and outline its benefits, particularly the potential for resolving tensions between water supply and demand. Integrated management is facilitated by combination with other stocks and flows frameworks that provide data on key drivers such as demography, land-use and electricity production.water accounts, stocks and flows, water budgets, decision support systems, strategic management

Conjugation of injections by permutations

Let X be a countably infinite set, and let f, g, and h be any three injective self-maps of X, each having at least one infinite cycle. (For instance, this holds if f, g, and h are not bijections.) We show that there are permutations a and b of X such that h=afa^{-1}bgb^{-1} if and only if |X\Xf|+|X\Xg|=|X\Xh|. We also prove a version of this statement that holds for infinite sets X that are not necessarily countable. This generalizes results of Droste and Ore about permutations.Comment: 27 pages, 4 figure

Experiments with hypersonic turbulent boundary layers on flat plates and delta wings

Hypersonic turbulent boundary layers on flat plates and delta wing