Can the turbulent galactic dynamo generate large-scale magnetic fields?

Large-scale magnetic fields in galaxies are thought to be generated by a turbulent dynamo. However the same turbulence also leads to a small-scale dynamo which generates magnetic noise at a more rapid rate. The efficiency of the large-scale dynamo depends on how this noise saturates. We examine this issue taking into account ambipolar drift, which obtains in a galaxy with significant neutral gas. We argue that, (1) the small-scale dynamo generated field does not fill the volume, but is concentrated into intermittent rope like structures. The flux ropes are curved on the turbulent eddy scales. Their thickness is set by the diffusive scale determined by the effective ambipolar diffusion; (2) For a largely neutral galactic gas, the small-scale dynamo saturates, due to inefficient random stretching, when the peak field in a flux rope has grown to a few times the equipartition value; (3) The average energy density in the saturated small-scale field is sub equipartition, since it does not fill the volume; (4) Such fields neither drain significant energy from the turbulence nor convert eddy motion of the turbulence on the outer scale into wavelike motion. The diffusive effects needed for the large-scale dynamo operation are then preserved until the large-scale field itself grows to near equipartition levels.Comment: 11 pages LaTeX, 2 postscript figures, included. Submitted to MNRA

The Use of Poly(vinyl alcohol)-based Hydrogels in Biomedical Applications

Polymers have found increasing favor in biomedical applications due to the greater control that researchers can exert over their properties. Researchers have focused on the development of therapies using biologically compatible polymers due to their ability to limit potentially harmful interactions with the body. This research has led to advances in tissue engineering, controlled and targeted drug delivery, and other biomedical fields, with the goal of improving both the effectiveness and accessibility of health care. Poly(vinyl alcohol) (PVA) hydrogels possess several chemical properties that make them well suited for biomedical applications. These include inertness and stability, biocompatibility, and pH-responsiveness. As a result, PVA based materials have been studied for potential applications in areas of biomedicine such as targeted drug delivery, tissue engineering, and wound healing. This thesis examines the properties of PVA and seeks to understand how the chemical and physical structure affects their properties. It then examines how these properties enhance their utility in potential biomedical applications. Finally, it reviews the research into development of PVA based materials for three different biomedical applications.Chemical Engineerin

Renminbi Rules: The Conditional Imminence of the Reserve Currency Transition

Against the backdrop of the recent financial crisis and the ongoing rapid changes in the world economy, the fate of the dollar as the premier international reserve currency is under scrutiny. This paper attempts to answer whether the Chinese renminbi will eclipse the dollar, what will be the timing of, and the prerequisites for this transition, and which of the two countries controls the outcome. The key finding, based on analyzing the last 110 years, is that the size of an economy—measured not just in terms of GDP but also trade and the strength of the external financial position—is the key fundamental correlate of reserve currency status. Further, the conventional view that sterling persisted well beyond the strength of the UK economy is overstated. Although the United States overtook the United Kingdom in terms of GDP in the 1870s, it became dominant in a broader sense encompassing trade and finance only at the end of World War I. And since the dollar overtook sterling in the mid-1920s, the lag between currency dominance and economic dominance was about 10 years rather than the 60-plus years traditionally believed. Applying these findings to the current context suggests that the renminbi could become the premier reserve currency by the end of this decade, or early next decade. But China needs to fulfill a number of conditions—making the reniminbi convertible and opening up its financial system to create deep and liquid markets—to realize renminbi preeminence. China seems to be moving steadily in that direction, and renminbi convertibility will proceed apace not least because it offers China's policymakers a political exit out of its mercantilist growth strategy. The United States cannot in any serious way prevent China from moving in that direction.Reserve Currency, Dollar, Sterling, Renminbi, China

Tricks with the lorenz curve

This note develops, for the Gini coefficient of inequality, a very simple generalization that directly incorporates judgments on ‘relative inter-group inequality aversion' by making the inequality measure sensitive to the skewness of the Lorenz curve. The resulting family of inequality indices can be seen as complements to the Gini coefficient: some members of the family reflect ‘left-leaning', and others ‘right-leaning', distributional values relative to the ‘centrist' position assumed by Gini.Lorenz Curve, Gini coefficient, skewness

Poverty Measurement and Theories of Beneficence

quantity, quality, inequality, identification, aggregation