We monitor the dynamics of superconducting vortices in the Bean state, as the system is driven to the threshold of instability by the slow ramping of an external field. Individual avalanches, containing as few as 50 vortices, are detected in real time. Thus our experiment is the superconducting analog of monitoring the granular avalanches produced by slowly dropping sand on a sandpile. The observed distribution of vortex avalanche sizes shows a power-law behavior over two decades, proving that the vortex dynamics in the Bean state is characterized by avalanches of many length scales.Some 30 years ago Bean [1] and de Gennes [2] noted the close analogy between the marginally stable state of vortices in a hard superconductor and the marginally stable slope of sand in a sandpile. We can picture building up a sandpile by slowly dropping grains on a flat surface. The slope of the pile soon reaches a certain "maximal angle of stability, " determined by a balance between gravity and intergrain frictional forces. A similar situation is present in a hard superconductor (i.e., with strong pinning).Vortices nucleate at the surface as an external magnetic field is slowly ramped. In the simplest model, due to Bean[1], the vortex density decreases linearly with distance into the superconductor. This again is due to a balance between vortex density gradients which drive vortices into the bulk and pinning forces which hamper their entry.These early analogies were invoked mainly in order to understand the static distribution of flux in a hard superconductor.More recently, interest has focused on the dynamics of systems slowly driven to the threshold of instability.A large number of diverse physical systems are characterized by such dynamics, including chargedensity waves, pinned Wigner crystals, earthquake faults, granular assemblies, and superconducting vortices. These systems have received renewed attention due to their relation to spatiotemporal dynamics, instabilities, and selforganized criticality. Sandpiles have received particularly intensive theoretical and experimental attention as a model system exhibiting such threshold dynamics.In light of the strong static analogies between sandpiles and the Bean state in hard superconductors, it is natural to ask whether there are quantitative similarities between the dynamic processes (e.g., similar avalanche size distributions) in the two systems.Here we report results of an experiment on the dynamics of vortices, which is closely analogous with those done on sandpiles. The magnetic field outside a tubular superconducting sample is ramped slowly, driving flux into the tube's outer wall. Eventually, the flux front will reach the 10-tI-~~&3 . -~gttI. 0 o C) D e Ic} 65 @o 1000 Ct 4T P 750 C, fP P P time or magnetic field FIG. 1. The voltage measured on the pickup coil as the magnetic field is ramped at 5 G/s. Frame (a) shows a 30 G segment centered at B = 7.55 kG. There are 262144 data points in this segment. The voltage trace consists of a series of many pulses, of widely varying siz...

In the last decade there have been marked reductions in malaria incidence in sub-Saharan Africa. Sustaining these reductions will rely upon insecticides to control the mosquito malaria vectors. We report that in the primary African malaria vector, Anopheles gambiae sensu stricto, a single enzyme, CYP6M2, confers resistance to two classes of insecticide. This is unique evidence in a disease vector of cross-resistance associated with a single metabolic gene that simultaneously reduces the efficacy of two of the four classes of insecticide routinely used for malaria control. The gene-expression profile of a highly DDT-resistant population of A. gambiae s.s. from Ghana was characterized using a unique whole-genome microarray. A number of genes were significantly overexpressed compared with two susceptible West African colonies, including genes from metabolic families previously linked to insecticide resistance. One of the most significantly overexpressed probe groups (false-discovery rate-adjusted P < 0.0001) belonged to the cytochrome P450 gene CYP6M2. This gene is associated with pyrethroid resistance in wild A. gambiae s.s. populations) and can metabolize both type I and type II pyrethroids in recombinant protein assays. Using in vitro assays we show that recombinant CYP6M2 is also capable of metabolizing the organochlorine insecticide DDT in the presence of solubilizing factor sodium cholate.

Adaptive introgression can provide novel genetic variation to fuel rapid evolutionary responses, though it may be counterbalanced by potential for detrimental disruption of the recipient genomic background. We examine the extent and impact of recent introgression of a strongly selected insecticide-resistance mutation (Vgsc-1014F) located within one of two exceptionally large genomic islands of divergence separating the Anopheles gambiae species pair. Here we show that transfer of the Vgsc mutation results in homogenization of the entire genomic island region (~1.5% of the genome) between species. Despite this massive disruption, introgression is clearly adaptive with a dramatic rise in frequency of Vgsc-1014F and no discernable impact on subsequent reproductive isolation between species. Our results show (1) how resilience of genomes to massive introgression can permit rapid adaptive response to anthropogenic selection and (2) that even extreme prominence of genomic islands of divergence can be an unreliable indicator of importance in speciation.

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We have measured the maximum field for which vortices are completely expelled from a thin-film superconducting strip. Niobium strips of width W were field cooled and imaged with a scanning Hall-probe microscope. Below a critical field B(m) approximately Phi(0)/W(2) all flux was expelled; above this field vortices were observed with a density increasing approximately linearly with field. The small value of the critical field, which is orders of magnitude less than in the bulk, implies that superconducting devices should be designed with narrow wires to eliminate the generation of noise from vortex motion.