4,805 research outputs found

    Mercury trends in cormorant and great blue heron eggs from Pacific Canada: a question of local and global sources

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    Mercury (Hg) levels and trends in the NE Pacific Ocean are due to the convergence between natural and anthropogenic sources, with the latter broadly related to a combination of local and long-range sources. Legacy and current local point sources include chlor-alkali plants, pulp and paper mills and other mixed sources. In addition, long-range atmospheric and oceanic pathways deliver mercury to the Pacific coast, primarily from points to the west, where it is taken up by algae and bacteria and transferred through the marine food web in its inorganic form, but also its organic form, methylmercury. We present data on Hg trends in pelagic cormorant ((Phalacrocorax pelagicus) and great blue heron (Ardea herodias) eggs in Pacific Canada over a 48 year period. Temporal trends are evaluated using both diet- and non-diet-adjusted data and compared to Hg trends observed in other seabird species in the region, as well as the Atlantic and Arctic Oceans. Mercury concentrations declined alongside δ34S over time in both species, but no trend for δ13C and δ15N was apparent. The present study provides explanations for these trends in the context of local and long-range sources in the region and dietary contributions

    Malaria elimination campaigns in the Lake Kariba region of Zambia: a spatial dynamical model

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    Background As more regions approach malaria elimination, understanding how different interventions interact to reduce transmission becomes critical. The Lake Kariba area of Southern Province, Zambia, is part of a multi-country elimination effort and presents a particular challenge as it is an interconnected region of variable transmission intensities. Methods In 2012-13, six rounds of mass-screen-and-treat drug campaigns were carried out in the Lake Kariba region. A spatial dynamical model of malaria transmission in the Lake Kariba area, with transmission and climate modeled at the village scale, was calibrated to the 2012-13 prevalence survey data, with case management rates, insecticide-treated net usage, and drug campaign coverage informed by surveillance. The model was used to simulate the effect of various interventions implemented in 2014-22 on reducing regional transmission, achieving elimination by 2022, and maintaining elimination through 2028. Findings The model captured the spatio-temporal trends of decline and rebound in malaria prevalence in 2012-13 at the village scale. Simulations predicted that elimination required repeated mass drug administrations coupled with simultaneous increase in net usage. Drug campaigns targeted only at high-burden areas were as successful as campaigns covering the entire region. Interpretation Elimination in the Lake Kariba region is possible through coordinating mass drug campaigns with high-coverage vector control. Targeting regional hotspots is a viable alternative to global campaigns when human migration within an interconnected area is responsible for maintaining transmission in low-burden areas

    Civil conflict, federalism and strategic delegation of leadership

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    This article analyzes negative externalities that policymakers in one region or group may impose upon the citizens of neighboring regions or groups. These externalities may be material, but they may also be psychological (in the form of envy). The latter form of externality may arise from the production of 'conspicuous' public goods. As a result, decentralized provision of conspicuous public goods may be too high. Potentially, a centralized legislature may internalize negative externalities. However, in a model with strategic delegation, we argue that the median voter in each jurisdiction may anticipate a reduction in local public goods supply and delegate to a policymaker who cares more for public goods than she does herself. This last effect mitigates the expected benefits of policy centralization. The authors' theory is then applied to the setting of civil conflict, where they discuss electoral outcomes in Northern Ireland and Yugoslavia before and after significant institutional changes that affected the degree of centralization. These case studies provide support for the authors' theoretical predictions

    Silicon-Based Antenna-Coupled Polarization-Sensitive Millimeter-Wave Bolometer Arrays for Cosmic Microwave Background Instruments

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    We describe feedhorn-coupled polarization-sensitive detector arrays that utilize monocrystalline silicon as the dielectric substrate material. Monocrystalline silicon has a low-loss tangent and repeatable dielectric constant, characteristics that are critical for realizing efficient and uniform superconducting microwave circuits. An additional advantage of this material is its low specific heat. In a detector pixel, two Transition-Edge Sensor (TES) bolometers are antenna-coupled to in-band radiation via a symmetric planar orthomode transducer (OMT). Each orthogonal linear polarization is coupled to a separate superconducting microstrip transmission line circuit. On-chip filtering is employed to both reject out-of-band radiation from the upper band edge to the gap frequency of the niobium superconductor, and to flexibly define the bandwidth for each TES to meet the requirements of the application. The microwave circuit is compatible with multi-chroic operation. Metalized silicon platelets are used to define the backshort for the waveguide probes. This micro-machined structure is also used to mitigate the coupling of out-of-band radiation to the microwave circuit. At 40 GHz, the detectors have a measured efficiency of 90%. In this paper, we describe the development of the 90 GHz detector arrays that will be demonstrated using the Cosmology Large Angular Scale Surveyor (CLASS) ground-based telescope
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