Sparse seismic imaging using variable projection

We consider an important class of signal processing problems where the signal of interest is known to be sparse, and can be recovered from data given auxiliary information about how the data was generated. For example, a sparse Green's function may be recovered from seismic experimental data using sparsity optimization when the source signature is known. Unfortunately, in practice this information is often missing, and must be recovered from data along with the signal using deconvolution techniques. In this paper, we present a novel methodology to simultaneously solve for the sparse signal and auxiliary parameters using a recently proposed variable projection technique. Our main contribution is to combine variable projection with sparsity promoting optimization, obtaining an efficient algorithm for large-scale sparse deconvolution problems. We demonstrate the algorithm on a seismic imaging example.Comment: 5 pages, 4 figure

Ecological thresholds and large carnivores conservation: Implications for the Amur tiger and leopard in China

The ecological threshold concept describes how changes in one or more factors at thresholds can result in a large shift in the state of an ecosystem. This concept focuses attention on limiting factors that affect the tolerance of systems or organisms and changes in them. Accumulating empirical evidence for the existence of ecological thresholds has created favorable conditions for practical application to wildlife conservation. Applying the concept has the potential to enhance conservation of two large carnivores, Amur tiger and leopard, and the knowledge gained could guide the construction of a proposed national park. In this review, ecological thresholds that result from considering a paradigm of bottom-up control were evaluated for their potential to contribute to the conservation of Amur tiger and leopard. Our review highlights that large carnivores, as top predators, are potentially affected by ecological thresholds arising from changes in climate (or weather), habitat, vegetation, prey, competitors, and anthropogenic disturbances. What's more, interactions between factors and context dependence need to be considered in threshold research and conservation practice, because they may amplify the response of ecosystems or organisms to changes in specific drivers. Application of the threshold concept leads to a more thorough evaluation of conservation needs, and could be used to guide future Amur tiger and leopard research and conservation in China. Such application may inform the conservation of other large carnivores worldwide

r-Process Nucleosynthesis in Shocked Surface Layers of O-Ne-Mg Cores

We demonstrate that rapid expansion of the shocked surface layers of an O-Ne-Mg core following its collapse can result in r-process nucleosynthesis. As the supernova shock accelerates through these layers, it makes them expand so rapidly that free nucleons remain in disequilibrium with alpha-particles throughout most of the expansion. This allows heavy r-process isotopes including the actinides to form in spite of the very low initial neutron excess of the matter. We estimate that yields of heavy r-process nuclei from this site may be sufficient to explain the Galactic inventory of these isotopes.Comment: 11 pages, 1 figure, to appear in the Astrophysical Journal Letter

Power-Law Distributions in Circulating Money: Effect of Preferential Behavior

We introduce preferential behavior into the study on statistical mechanics of money circulation. The computer simulation results show that the preferential behavior can lead to power laws on distributions over both holding time and amount of money held by agents. However, some constraints are needed in generation mechanism to ensure the robustness of power-law distributions.Comment: 4 pages, 2 figure

Explanation of the RHIC HBT Puzzle by a Granular Source of Quark-Gluon Plasma Droplets

We present a review on the explanation of the RHIC HBT puzzle by a granular pion-emitting source of quark-gluon plasma droplets. The evolution of the droplet is described by relativistic hydrodynamics with an equation of state suggested by lattice gauge results. The granular source evolution is obtained by superposing all of the evolutions of individual droplets. Pions are assumed to be emitted thermally from the droplets at the freeze-out configuration characterized by a freeze-out temperature $T_f$. We find that the average particle emission time scales with the initial radius of the droplet. Pions will be emitted earlier if the droplet radius is smaller. An earlier emission time will lead to a smaller extracted HBT radius $R_{\rm out}$, while the extracted HBT radius $R_{\rm side}$ is determined by the scale of the distribution of the droplet centers. However, a collective expansion of the droplets can further decrease $R_{\rm out}$. As a result, the value of $R_{\rm out}/R_{\rm side}$ can be close to, or even less than 1 for theComment: 8 pages, 4 figures, invited talk presented at the XI International Workshop on Correlation and Fluctuation in Multiparticle Production, Nov. 21-24, 2006, Hangzhou, Chin

Reverse Osmosis Chemistry — Basics, Barriers and Breakthroughs

While reverse osmosis (RO) for desalination of brackish water, seawater and wastewater is a most economical and powerful method, its sensitivity to fouling points to the importance of understanding the water chemistry involved and methods of fouling control and system maintenance. As a chemical developer of antiscalants, antifoulants, and operation and maintenance chemicals needed for RO systems, we present here a basic understanding of RO chemistry, the challenges of scaling and colloidal fouling that limits % recovery of permeate and some breakthroughs we have attained