3,636 research outputs found

    Distributions and abundances of Pacific sardine (Sardinops sagax) and other pelagic fishes in the California Current Ecosystem during spring 2006, 2008, and 2010, estimated from acoustic–trawl surveys

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    The abundances and distributions of coastal pelagic fish species in the California Current Ecosystem from San Diego to southern Vancouver Island, were estimated from combined acoustic and trawl surveys conducted in the spring of 2006, 2008, and 2010. Pacific sardine (Sardinops sagax), jack mackerel (Trachurus symmetricus), and Pacific mackerel (Scomber japonicus) were the dominant coastal pelagic fish species, in that order. Northern anchovy (Engraulis mordax) and Pacific herring (Clupea pallasii) were sampled only sporadically and therefore estimates for these species were unreliable. The estimates of sardine biomass compared well with those of the annual assessments and confirmed a declining trajectory of the “northern stock” since 2006. During the sampling period, the biomass of jack mackerel was stable or increasing, and that of Pacific mackerel was low and variable. The uncertainties in these estimates are mostly the result of spatial patchiness which increased from sardine to mackerels to anchovy and herring. Future surveys of coastal pelagic fish species in the California Current Ecosystem should benefit from adaptive sampling based on modeled habitat; increased echosounder and trawl sampling, particularly for the most patchy and nearshore species; and directed-trawl sampling for improved species identification and estimations of their acoustic target stre

    Noether symmetries, energy-momentum tensors and conformal invariance in classical field theory

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    In the framework of classical field theory, we first review the Noether theory of symmetries, with simple rederivations of its essential results, with special emphasis given to the Noether identities for gauge theories. Will this baggage on board, we next discuss in detail, for Poincar\'e invariant theories in flat spacetime, the differences between the Belinfante energy-momentum tensor and a family of Hilbert energy-momentum tensors. All these tensors coincide on shell but they split their duties in the following sense: Belinfante's tensor is the one to use in order to obtain the generators of Poincar\'e symmetries and it is a basic ingredient of the generators of other eventual spacetime symmetries which may happen to exist. Instead, Hilbert tensors are the means to test whether a theory contains other spacetime symmetries beyond Poincar\'e. We discuss at length the case of scale and conformal symmetry, of which we give some examples. We show, for Poincar\'e invariant Lagrangians, that the realization of scale invariance selects a unique Hilbert tensor which allows for an easy test as to whether conformal invariance is also realized. Finally we make some basic remarks on metric generally covariant theories and classical field theory in a fixed curved bakground.Comment: 31 pa

    Effect of anisotropic impurity scattering on a density of states of a d-wave superconductor

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    We discuss the effect of an anisotropic impurity potential on the critical temperature, local density of states in the vicinity of a single impurity, and the quasiparticle density of states for a finite impurity concentration in a d-wave superconductor. Different scattering regimes are concerned.Comment: 3 pages, revtex4, 4 figure

    Local Electronic Structure of a Single Magnetic Impurity in a Superconductor

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    The electronic structure near a single classical magnetic impurity in a superconductor is determined using a fully self-consistent Koster-Slater algorithm. Localized excited states are found within the energy gap which are half electron and half hole. Within a jellium model we find the new result that the spatial structure of the positive-frequency (electron-like) spectral weight (or local density of states), can differ strongly from that of the negative frequency (hole-like) spectral weight. The effect of the impurity on the continuum states above the energy gap is calculated with good spectral resolution for the first time. This is also the first three-dimensional self-consistent calculation for a strong magnetic impurity potential.Comment: 13 pages, RevTex, change in heuristic picture, no change in numerical result

    Non-magnetic impurities in two dimensional superconductors

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    A numerical approach to disordered 2D superconductors described by BCS mean field theory is outlined. The energy gap and the superfluid density at zero temperature and the quasiparticle density of states are studied. The method involves approximate self-consistent solutions of the Bogolubov-de \,Gennes equations on finite square lattices. Where comparison is possible, the results of standard analytic approaches to this problem are reproduced. Detailed modeling of impurity effects is practical using this approach. The {\it range} of the impurity potential is shown to be of {\it quantitative importance} in the case of strong potential scatterers. We discuss the implications for experiments, such as the rapid suppression of superconductivity by Zn doping in Copper-Oxide superconductors.Comment: 16 pages, latex, 8 figures( available upon request

    Obtaining Stakeholder Consensus on the Core Components of a Parent Support and Training Model for Parents of Children With Serious Emotional Disturbances

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    This is the publisher's version, also available electronically from http://alliance1.metapress.com/content/y66232237182170g/?genre=article&id=doi%3a10.1606%2f1044-3894.4317Parent-to-parent peer interventions are nationally recognized as an important service within children's community-based mental health systems of care. Despite rapid growth, clearly defined models of professional parent services for statewide application do not exist. In this study, concept mapping was used to achieve stakeholder consensus on the core components of the Parent Support and Training (PST) peer intervention model developed within the Kansas community mental health system. Participants rated the importance and observed frequency of 49 distinct statements related to the service and sorted them into conceptual groups. Analyses reflected a high level of agreement across stakeholders on statements identified as most important and most frequently demonstrated in PST services statewide

    Extended Impurity Potential in a d_{x^2-y^2} Superconductor

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    We investigate the role of a finite potential range of a nonmagnetic impurity for the local density of states in a d_{x^2-y^2} superconductor. Impurity induced subgap resonances are modified by the appearance of further scattering channels beyond the ss--wave scattering limit. The structure of the local density of states (DOS) in the vicinity of the impurity is significantly enhanced and therefore improves the possibility for observing the characteristic anisotropic spatial modulation of the local DOS in a d_{x^2-y^2} superconductor by scanning tunneling microscopy.Comment: 4 pages, Revtex, with 4 embedded eps figures. Submitted to Phys. Rev. Let

    Permanent current from non-commutative spin algebra

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    We show that a spontaneous electric current is induced in a nano-scale conducting ring just by putting three ferromagnets. The current is a direct consequence of the non-commutativity of the spin algebra, and is proportional to the non-coplanarity (chirality) of the magnetization vectors. The spontaneous current gives a natural explanation to the chirality-driven anomalous Hall effect.Comment: 7 pages, 4 figures on separate pag

    Quantitative LSPR Imaging for Biosensing with Single Nanostructure Resolution

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    AbstractLocalized surface plasmon resonance (LSPR) imaging has the potential to map complex spatio-temporal variations in analyte concentration, such as those produced by protein secretions from live cells. A fundamental roadblock to the realization of such applications is the challenge of calibrating a nanoscale sensor for quantitative analysis. Here, we introduce a new, to our knowledge, LSPR imaging and analysis technique that enables the calibration of hundreds of individual gold nanostructures in parallel. The calibration allowed us to map the fractional occupancy of surface-bound receptors at individual nanostructures with nanomolar sensitivity and a temporal resolution of 225 ms. As a demonstration of the technique’s applicability to molecular and cell biology, the calibrated array was used for the quantitative LSPR imaging of anti-c-myc antibodies harvested from a cultured 9E10 hybridoma cell line without the need for further purification or processing
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