Sparsity and persistence: mixed norms provide simple signal models with dependent coefficients

Sparse regression often uses ℓ _p norm priors (with p < 2). This paper demonstrates that the introduction of mixed-norms in such contexts allows one to go one step beyond in signal models, and promote some different, structured, forms of sparsity. It is shown that the particular case of the ℓ_1,2 and ℓ_2,1 norms leads to new group shrinkage operators. Mixed norm priors are shown to be particularly efficient in a generalized basis pursuit denoising approach, and are also used in a context of morphological component analysis. A suitable version of the Block Coordinate Relaxation algorithm is derived for the latter. The group-shrinkage operators are then modified to overcome some limitations of the mixed-norms. The proposed group shrinkage operators are tested on simulated signals in specific situations, to illustrate and compare their different behaviors. Results on real data are also used to illustrate the relevance of the approach.     

Systematics and Optimisation of Hole Doping in Bi-2223

We report systematic changes in thermopower, T _c , Raman modes and magnetic irreversibility H _irr as a function of carrier hole concentration p in Bi-2223. We have established that Raman spectroscopy can provide an indicator of doping level: the 630cm ^–1 mode is found to soften with increasing p. A departure of the thermopower from the universal thermopower-doping relationship displayed by other HTS compounds is explained by a non-uniform charge distribution over the three CuO ₂ planes. Scaling of H _irr shows the optimal hole concentration for maximum J _c lies beyond currently achieved levels.     

Development of a universal modeling tool for rechargeable lithium batteries

An interesting universal modeling tool for rechargeable lithium batteries is presented in this paper. The generic model is based on an equivalent circuit technique commonly used in electrochemical impedance characterization. Therefore, the parameters used in the model can be easily parameterized from the electrochemical impedance derivations, which provide a convenient integration with experimental cell characterizations. Such integration offers the universality in this modeling approach.     

Measurement and scaling of air-surface mercury exchange from substrates in the vicinity of two Nevada gold mines

The state of Nevada has extensive mineral resources, and is the largest producer of gold in the USA as well as fourth in world gold production. Mercury (Hg) is often present in the hydrothermal systems that produce gold deposits, and can be found in elevated concentrations in gold ore. As a result, mining of gold ore in Nevada has been shown to release Hg to the atmosphere from point and non-point sources. This project focused on measurement of air-soil Hg exchange associated with undisturbed soils and bedrock outcrops in the vicinity of two large gold mines. Field and laboratory data collected were used to identify the important variables controlling Hg flux from these surfaces, and to estimate a net flux from the areas adjacent to the active mines as well as that occurring from the mined area pre-disturbance. Mean daily flux by substrate type ranged from 9 ng m^− 2 day^− 1 to 140 ng m^− 2 day^− 1. Periods of net deposition of elemental Hg were observed when air masses originating from a mine site moved over sampling locations. Based on these observations and measured soil Hg concentrations we suggest that emissions from point and non-point sources at the mines are a source of Hg to the surrounding substrates with the amount deposited not being of an environmental concern but of interest mainly with respect to the cycling of atmospheric elemental Hg. Observations indicate that while some component of the deposited Hg is sequestered in the soil, this Hg is gradually released back to the atmosphere over time. Estimated pre-disturbance emissions from the current mine footprints based on field data were 0.1 and 1.7 kg yr^− 1, compared to that estimated for the current non-point mining sources of 19 and 109 kg yr^− 1, respectively.     

The effect of external flow on the feeding currents of sessile microorganisms

Microscopic sessile suspension feeders live attached to surfaces and, by consuming bacteria-sized prey and by being consumed, they form an important part of aquatic ecosystems. Their environmental impact is mediated by their feeding rate, which depends on a self-generated feeding current. The feeding rate has been hypothesized to be limited by recirculating eddies that cause the organisms to feed from water that is depleted of food particles. However, those results considered organisms in still water, while ambient flow is often present in their natural habitats. We show, using a point-force model, that even very slow ambient flow, with speed several orders of magnitude less than that of the self-generated feeding current, is sufficient to disrupt the eddies around perpendicular suspension feeders, providing a constant supply of food-rich water. However, the feeding rate decreases in external flow at a range of non-perpendicular orientations due to the formation of recirculation structures not seen in still water. We quantify the feeding flow and observe such recirculation experimentally for the suspension feeder Vorticella convallaria in external flows typical of streams and rivers.     

Ion beam switching magnet employing HTS coils

This paper describes the design, construction, and testing of an ion beam switching high-temperature superconducting (HTS) magnet installed at Institute of Geological and Nuclear Science (IGNS) in New Zealand. It was designed by a consortium comprising American Superconductor Corporation (ASC), ISYS, Applied Engineering Technologies (AET), the New Zealand Institute for Industrial Research and Development (IRL), and Alphatech. The work was also supported in part by New Zealand Foundation for Research and Technology-Technology for Business Growth Programme. The magnet generates 0.72 T in the airgap between two 410×700 mm warm iron poles. The Bi-2223 HTS coils are conduction-cooled with a single stage Gifford-McMahon (G-M) type cryocooler for steady-state operation. The magnet was fully tested at ASC during the fall of 1996. This represents the first large-scale fully operational HTS physics magnet announced so far. The successful operation of this magnet has verified maturation of HTS magnet technology employing conduction cooling techniques with G-M type cryocoolers. Long term operation of this magnet in continuous use will prove the reliability of HTS magnet systems in critical applications and is expected to open future opportunities for HTS in other related areas