Nonlocal Optics of Plasmonic Nanowire Metamaterials

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

Evaluation of Fish Scale Chemistry for Determining Habitat Associations

This is the first work examining the utility of scale chemistry for determining natal origins and habitat associations. I quantified a relationship of scale chemistry to water chemistry, quantified geographic variation in scale chemistry, and evaluated stability of scale chemistry through maturation. Scale chemistry accurately reflected trace element composition of the water in which fish had lived. Juvenile spot (Leiostomus xanthurus) were held in four concentrations of Sr, Cd, and Ba maintained at either 20°C or 25°C, for 42 days. Strontium:Ca, Cd:Ca, and Ba:Ca levels in scales were linearly related to environmental concentrations while temperature had no effect. These results suggested scale chemistry could reflect differences related to habitat use by fishes. To test this, Mg:Ca, Mn:Ca, Sr:Ca, and Ba:Ca levels in scales from juvenile weakfish (Cynoscion regalis) from five estuaries along the Atlantic coast were measured. Significant variability in multivariate elemental signatures was found among estuaries and between collections from 1996 and 1997. Linear discriminant function analysis was used to classify individual juvenile weakfish to natal estuary with ∼65% accuracy. Results from simulated learning and test samples derived from the juvenile data indicated a maximum likelihood (ML) procedure could estimate proportions of juveniles from each natal estuary with ∼90–95% accuracy. Inter-annual variability in the trace element signatures meant fish could not be accurately classified to natal estuary based on signatures collected from juvenile fish in a different year. Trace element levels in scales were significantly correlated with otolith concentrations from the same fish in both studies, suggesting that similar processes control both scale and otolith chemistries. Finally, using natal-estuary signatures, natal location of adult weakfish collected in Pamlico Sound, Chesapeake Bay, and Delaware Bay was estimated with ML. Composition of adults was estimated similarly by otolith and scale chemistries. However, these data suggested that scale chemistry was not stable after the juvenile period possibly due to continued crystallization. In all, at least some trace elements in scales reflect levels in the ambient environment, and may be useful for quantifying life-history characteristics of individual fish. However, caution is required when applying the technique to adults as elemental signatures may degrade

New Cooperative Development Issues

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,

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

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

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

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

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

Immunization status and child survival in rural Ghana

For three decades, the Expanded Programme on Immunization (EPI) has been promoted as one of the key child health interventions in developing countries. Vaccines for six childhood diseases (diphtheria, measles, pertussis, poliomyelitis, tetanus, and tuberculosis) have been shown to be efficacious in preventing disease-specific morbidity and mortality, yet not all commentators are convinced that the EPI reduces all-cause child mortality. Numerous studies have found that measles vaccination programs substantially reduce all-cause child mortality, but recent findings from Guinea-Bissau suggest that diphtheria, pertussis, and tetanus (DPT) vaccine may increase all-cause child mortality. The present study uses five years of data from the Navrongo Demographic Surveillance System, a longitudinal population registration system in northern Ghana, to examine all-cause mortality among vaccinated and unvaccinated children under 5 years of age. The data indicate that coverage by one Bacillus Calmette-Guerin (BCG) shot, three sets of polio drops, and three DPT shots reduces mortality between ages 4 and 8 months by nearly 90 percent. Complete coverage by all EPI antigens reduces mortality between ages 9 and 59 months by 70 percent. BCG, polio, and DPT vaccines without measles vaccination reduce mortality by 40 percent. The independent reduction in mortality associated with measles vaccination is 50 percent. Our data add to a growing body of evidence that suggests that measles vaccination programs reduce all-cause mortality substantially beyond the proportion of deaths caused by measles. These results indicate a need for further research in developing countries on the all-cause mortality impact of these vaccines, in particular DPT vaccine