1,412 research outputs found

    Nonlocal Optics of Plasmonic Nanowire Metamaterials

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    We present an analytical description of the nonlocal optical response of plasmonic nanowire metamaterials that enable negative refraction, subwavelength light manipulation, and emission lifetime engineering. We show that dispersion of optical waves propagating in nanowire media results from coupling of transverse and longitudinal electromagnetic modes supported by the composite and derive the nonlocal effective medium approximation for this dispersion. We derive the profiles of electric field across the unit cell, and use these expressions to solve the long-standing problem of additional boundary conditions in calculations of transmission and reflection of waves by nonlocal nanowire media. We verify our analytical results with numerical solutions of Maxwell's equations and discuss generalization of the developed formalism to other uniaxial metamaterials

    Age, Growth, and Mortality of Black Drum, Pogonias cromis, in the Chesapeake Bay Region

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    We used otolith ageing to describe the population dynamics of black drum, Pogonias cromis, collected over a three-year period from the Chesapeake Bay region\u27s commercial and recreational fisheries. Black drum average age, total length, and weight were 26 years, 109.5 cm, and 22.1 kg respectively. The oldest fish was 59 years and fish older than 50 years were present in the catch from 1990 to 1992. Growth in length slowed by age 20, whereas growth in weight did not slow until age 45. A von Bertalanffy growth function was fitted to our data (L(infinity) = 117.3 cm, K=0.105, t(0)=-2.3 yr) and was similar to that for northeast Florida, but dissimilar to that for the Gulf of Mexico. Fish grow slower but reach larger sizes in the Atlantic than in the Gulf. Estimates of instantaneous total mortality, Z, from maximum age and catch-curve analyses were low, 0.08-0.13, indicating that fishing mortality is also low in the Chesapeake Bay region. Studies to date lend support to the hypothesis that black drum from the east coast of the United States are from a common stock. The fishery of the Chesapeake Bay region is made up of old, large migrants from that larger population and should be managed accordingly

    New Cooperative Development Issues

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    This article briefly reviews the increased interest in new cooperative development, factors for successful cooperative development, and strategies to improve the performance of new and emerging cooperatives. The article highlights issues identified by a panel of cooperative leaders, USDA specialists and academic expertsCooperatives, New Cooperatives, Developing Cooperatives, Agribusiness, P13, L22, L43,

    Reproduction of Black Drum, Pogonias cromis, from the Chesapeake Bay Region

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    Ovaries of black drum, Pogonias cromis, collected from the Chesapeake Bay region in 1992, were used to describe reproductive strategy and fecundity. Histological examination showed that black drum spawn in the Chesapeake Bay region from April through early June. Distributions of oocyte diameter showed distinct oocyte-developmental groups indicating that Chesapeake Bay black drum are group-synchronous batch spawners. Female black drum are extremely fecund ranging from 414,000 to 3,736,000 hydrated oocytes (mean = 1,389,000) per batch with a spawning periodicity of 3.8 days. Estimates of spawning strategy, spawning periodicity, and batch fecundity for black drum from the Chesapeake Bay region were similar to reported estimates from the Gulf of Mexico

    Yield-Per-Recruit Analysis for Black Drum, Pogonias cromis, Along the East Coast of the United States and Management Strategies for Chesapeake Bay

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    Black drum, Pogonias cromis along the U.S. East Coast is subject to commercial and recreational harvest. However, prior to this study no modeling had been undertaken to examine the potential for overfishing in the Chesapeake Bay region. We present evidence from yield-per-recruit models that growth overfishing of black drum is unlikely under current fishing practices in this region. Particular attention was given to fishing practices in the Chesapeake Bay region where old, large fish predominate in the commercial and recreational catches (mean age=26 years: mean total length=108.4 cm; mean weight 22.1 kg). Yield-per-recruit model results showed that growth overfishing was unlikely in the Chesapeake Bay region under all but the lowest estimates of natural mortality (M=0.02-0.04). Such extreme low values of M predict potential life span of 200 years and were dismissed as improbable-the oldest age recorded for this species is 59 years. Additionally, biomass-per-recruit model results indicated a 42-59% decrease to current biomass from the unfished stock. The apparent age-specific migration of this stock argues for protection of young fish that have dominated the catch in Northeast Florida. Modeling indicated that growth overfishing could result from heavy fishing on these young ages and would all but eliminate this resource of the northern fishery

    Scanning in Situ Spectroscopy Pplatform for Imaging Surgical Breast Tissue Specimens

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    A non-contact localized spectroscopic imaging platform has been developed and optimized to scan 1 x 1 cmΒ² square regions of surgically resected breast tissue specimens with ~150-micron resolution. A color corrected, image-space telecentric scanning design maintained a consistent sampling geometry and uniform spot size across the entire imaging field. Theoretical modeling in ZEMAX allowed estimation of the spot size, which is equal at both the center and extreme positions of the field with ~5% variation across the designed waveband, indicating excellent color correction. The spot sizes at the center and an extreme field position were also measured experimentally using the standard knife-edge technique and were found to be within ~8% of the theoretical predictions. Highly localized sampling offered inherent insensitivity to variations in background absorption allowing direct imaging of local scattering parameters, which was validated using a matrix of varying concentrations of Intralipid and blood in phantoms. Four representative, pathologically distinct lumpectomy tissue specimens were imaged, capturing natural variations in tissue scattering response within a given pathology. Variations as high as 60% were observed in the average reflectance and relative scattering power images, which must be taken into account for robust classification performance. Despite this variation, the preliminary data indicates discernible scatter power contrast between the benign vs malignant groups, but reliable discrimination of pathologies within these groups would require investigation into additional contrast mechanisms
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