299,041 research outputs found

    Interaction effects on almost flat surface bands in topological insulators

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    We consider ferromagnetic instabilities of two-dimensional helical Dirac fermions hosted on the surface of three-dimensional topological insulators. We investigate ways to increase the role of interactions by means of modifying the bulk properties which in turn changes both the surface Dirac theory and the screening of interactions. We discuss both the long-ranged part of the Coulomb interactions controlled by the dimensionless coupling constant őĪ=e2/(‚ĄŹŌĶvFsurf)\alpha = e^{2}/(\hbar \epsilon v_{F}^{\mathrm{surf}}) as well as the effects of local interactions parametrized by the ratio Usurf/DsurfU_{\mathrm{surf}}/D_{\mathrm{surf}} of a local interaction on the surface, UsurfU_{\mathrm{surf}}, and the surface bandwidth, DsurfD_{\mathrm{surf}}. If large compared to 1, both mechanisms can induce spontaneously surface ferromagnetism, thereby gapping the surface Dirac metal and inducing an anomalous quantum Hall effect. We investigate two mechanisms which can naturally lead to small Fermi velocities vFsurfv_{F}^{\mathrm{surf}} and a corresponding small bandwidth DsurfD_{\mathrm{surf}} at the surface when the bulk band gap is reduced. The same mechanisms can, however, also lead to an enhanced screening of surface interactions. While in all considered cases the long-ranged part of the Coulomb interaction is screened efficiently, őĪ‚Č≤1\alpha \lesssim 1, we discuss situations, where Usurf/DsurfU_{\mathrm{surf}}/D_{\mathrm{surf}} becomes \emph{parametrically}\ large compared to 1, thus inducing surface magnetism.Comment: 15 pages, 8 figures, published version with minor updat

    Observations of an Alligator (Alligator mississippiensis) Nest and Behavior of Hatchlings in Clark County, with anecdotal observations of other Alligator Nests in Arkansas

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    Historically, the American alligator (Alligator mississippiensis) ranged through southern and much of eastern Arkansas. By the early 1900s, alligator populations had declined due to unregulated hunting, commercial exploitation, and habitat loss. In 1961, the Arkansas Game and Fish Commission (AGFC) established protection of this species, and in 1967 the U.S. Fish and Wildlife Service listed the alligator as an endangered species. The AGFC conducted a restocking program from 1972-1984, and the species made a full recovery in Arkansas. Still, little is known about reproductive biology in the state. We observed an alligator nest near Arkadelphia, Clark Co., the mound of which was 1.6 m long, 1.3 m across, and 43-56 cm in height. Because the nest had not hatched by a date late for the species, we opened the nest because some peeping by live hatchlings could be heard. The nest contained 33 eggs, of which 12 hatched the rest were unfertile or died early. We observed behaviors of baby alligators at the time of hatching from a wild nest, and the development of feeding behaviors while maintained in lab. Babies were aggressive and bit debris and each other while hatching, apparently to aid in their exit from the egg. Aggressive behaviors subsided, and young took crickets, earthworms, and shiners as food. After about 3 days, individuals who both grabbed parts of a shiner or earthworm began the spin behaviors to tear apart food items

    SenseCam image localisation using hierarchical SURF trees

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    The SenseCam is a wearable camera that automatically takes photos of the wearer's activities, generating thousands of images per day. Automatically organising these images for efficient search and retrieval is a challenging task, but can be simplified by providing semantic information with each photo, such as the wearer's location during capture time. We propose a method for automatically determining the wearer's location using an annotated image database, described using SURF interest point descriptors. We show that SURF out-performs SIFT in matching SenseCam images and that matching can be done efficiently using hierarchical trees of SURF descriptors. Additionally, by re-ranking the top images using bi-directional SURF matches, location matching performance is improved further

    The problem with the SURF scheme

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    There is a serious problem with one of the assumptions made in the security proof of the SURF scheme. This problem turns out to be easy in the regime of parameters needed for the SURF scheme to work. We give afterwards the old version of the paper for the reader's convenience.Comment: Warning : we found a serious problem in the security proof of the SURF scheme. We explain this problem here and give the old version of the paper afterward

    SurF: an innovative framework in biosecurity and animal health surveillance evaluation

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    Surveillance for biosecurity hazards is being conducted by the New Zealand Competent Authority, the Ministry for Primary Industries (MPI) to support New Zealand's biosecurity system. Surveillance evaluation should be an integral part of the surveillance life cycle, as it provides a means to identify and correct problems and to sustain and enhance the existing strengths of a surveillance system. The surveillance evaluation Framework (SurF) presented here was developed to provide a generic framework within which the MPI biosecurity surveillance portfolio, and all of its components, can be consistently assessed. SurF is an innovative, cross‚Äźsectoral effort that aims to provide a common umbrella for surveillance evaluation in the animal, plant, environment and aquatic sectors. It supports the conduct of the following four distinct components of an evaluation project: (i) motivation for the evaluation, (ii) scope of the evaluation, (iii) evaluation design and implementation and (iv) reporting and communication of evaluation outputs. Case studies, prepared by MPI subject matter experts, are included in the framework to guide users in their assessment. Three case studies were used in the development of SurF in order to assure practical utility and to confirm usability of SurF across all included sectors. It is anticipated that the structured approach and information provided by SurF will not only be of benefit to MPI but also to other New Zealand stakeholders. Although SurF was developed for internal use by MPI, it could be applied to any surveillance system in New Zealand or elsewhere

    Efficient storage and decoding of SURF feature points

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    Practical use of SURF feature points in large-scale indexing and retrieval engines requires an efficient means for storing and decoding these features. This paper investigates several methods for compression and storage of SURF feature points, considering both storage consumption and disk-read efficiency. We compare each scheme with a baseline plain-text encoding scheme as used by many existing SURF implementations. Our final proposed scheme significantly reduces both the time required to load and decode feature points, and the space required to store them on disk

    Species composition and catch per unit of effort of Monterey Bay surf, pier, and skiff anglers in 1979

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    In 1979, Monterey Bay sport anglers were sampled for species composition of the catch and catch per unit of effort. A total of 4150 surf, pier, and skiff anglers was interviewed. Catch per hour was 0.71, 0.58, and 1.25 for surf, pier, and skiff anglers, respectively. Barred surfperch, Amphisticus argenteus, totaled 76% of the surf catch. The species composition of the pier catch was dominated by juvenile bocaccio, Sebastes paucispinis; white croaker, Genyonemus lineatus; and walleye surfperch, Hyperprosopon argenteum. The skiff fishery was dominated by sanddabs, Citharichthys spp., and blue rockfish, Sebastes mystinus. The best surf fishing area was between Palm Beach and Sand Dollar Beach in northern Monterey Bay, while Monterey Wharf No. 2 was the best public fishing pier. However, a small privately operated pier inside Moss Landing Harbor had the best catch rate (2.44 fish per h) of all piers sampled. (23pp.
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