Incidence of mayfly (Povilla sp.) infestation of wooden infrastructures of artisanal fishers in the lagoon and marine fisheries locations of Ogun State, Nigeria

A diagnostic survey of the incidence of mayfly (Povilla sp.) infestation of wooden infrastructures of the artisanal fishers in ten (10) lagoons and marine fishing villages of Ogun States (Nigeria) was carried out through the application of structured questionnaire and participatory Rural Appraisal interviews. The demographic, infrastructural and socioeconomic characteristics of the ten fishing villages sampled were derived and analyzed. The infestation which occurs all year round is found to be most prevalent (70%) in the wet season, increasing proportionally with salinity from 56% (brackish water); to 63% (marine water). The life-span of Povilla sp. is reduced from 55% to 62% (freshwater); 41% (brackish water) and 38% (marine water). Annual financial loss of N10,000.00 per fisher or N80,000,000.00 to the 8000 artisanal fishers affected in Ogun State is discussed. It is recommended that fishers should preferably use non-wood crafts and infrastructures while adopting appropriate management strategies for containing the existing infestatio

Food and feeding habits of Synodontis nigrita from the Osun River, SW Nigeria

An investigation was conducted into the food and feeding habits of Synodontis nigrita from the Osun River near Epe, Lagos, Nigeria. The food items in the stomach of the S. nigrita covered a wide spectrum, ranging from various types of plankton to invertebrates and plants. A seasonal variation was also noted in the stomach contents of S. nigrita over the period of investigation. The predominant food items found in the stomach were Polycystis spp., Closterium spp., Oedogonium spp., plant tissues, insect parts and detritus. This suggests that S. nigrita is an omnivore

A joint-channel diagonalization for multiuser MIMO antenna systems

In this paper, we address the problem of improving the performance of multiuser space-division multiplexing (SDM) systems where multiple independent signal streams can be transmitted in the same frequency and time slot. The problem is important in multiuser multiple-input multiple-output systems where communication from one base station to many mobile stations can occur simultaneously. Our objective is to devise a multiuser linear space-time precoder for simultaneous channel diagonalization of the multiuser channels enabling SDM. Our new approach is based on diagonalizing the multiuser channel matrices and we use a variation of successive Jacobi rotations. In addition to the diagonalization, our approach attempts to optimize the resultant channel gains for performance enhancement. Our method is valid for both frequency-flat and frequency-selective fading channels but we assume that the base station knows all the channels and that they are quasi-stationary

Introgression in interspecific hybrids of lily

In order to introduce new desirable characters into the cultivar assortment of lily a range of interspecific crossing barriers has to be overcome. By using various pollination and embryo rescue techniques pre- and postfertilization barriers were overcome and a range of wide interspecific lily hybrids between species and cultivars from the different sections of the genus Lilium could be made. Important breakthroughs include the development of the LA- (L. longiflorum x Asiatic hybrids), the LO- (L. longiflorum x Oriental hybrids) and the OA- (Oriental x Asiatic hybrids) hybrids. In general wide interspecific lily hybrids show F1-sterility. Using somatic chromosome doubling techniques (mitotic polyploidization) tetraploids with restored fertility can be produced from these diploid hybrids. An alternative method is the use of unreduced (or 2n) gametes (meiotic polyploidization), which are rarely found in some hybrids. Introgression of alien chromosome segments from donor species into recipient cultivar through backcrossing of F1 hybrid was studied using in situ hybridization techniques (GISH). Mitotic polyploidization showed no homoeologous recombinations between the parental genomes whereas meiotic polyploidization detected many. The use of 2n-gametes seems to be the most promising way for the introgression of desirable characters

The Effects of Uncertainty on Macroeconomic Performance: The Importance of the Conditional Covariance Model.

We study the effects of growth volatility and inflation volatility on average rates of output growth and inflation for postwar U.S. data in a multivariate asymmetric GARCH-M model. Our statistical model differs from other work in that we allow the conditional covariance of inflation and growth to be both nondiagonal and asymmetric. We show that the data reject diagonality and symmetry restrictions frequently imposed in the literature. Our results on the macroeconomic effects of uncertainty also differ from those in other recent studies using a more restrictive covariance model. Specifically, we find that increased growth uncertainty is associated with significantly higher average growth, and that higher inflation uncertainty is significantly negatively correlated with lower output growth and lower average inflation.Asymmetry; Multivariate GARCH-M; Inflation; Uncertainty; Growth

Food and feeding habits of Synodontis nigrita from the Osun River, SW Nigeria

An investigation was conducted into the food and feeding habits of Synodontis nigrita from the Osun River near Epe, Lagos, Nigeria. The food items in the stomach of the S. nigrita covered a wide spectrum, ranging from various types of plankton to invertebrates and plants. A seasonal variation was also noted in the stomach contents of S. nigrita over the period of investigation. The predominant food items found in the stomach were Polycystis spp., Closterium spp., Oedogonium spp., plant tissues, insect parts and detritus. This suggests that S. nigrita is an omnivore.Feeding behaviour, Stomach content, Food consumption, Nigeria, Synodontis nigrita

Axiomization of the center function on trees.

We give a new, short proof that four certain axiomatic properties uniquely define the center of a tree.

Development of catalytic hydrogenation reactors for the fine chemicals industry

A survey is given of the problems to be solved before catalytic hydrogenation reactors can be applied in a multiproduct plant in which selectivity problems are experienced. Some results are reported on work done on the reaction kinetics of two multistep model reactions and on mathematical modelling and experimental verification of the models. Since hydrogenation reactions are often very exothermic, cooling by solvent evaporation has been applied where appropriate. Sufficient information has been collected and correlated to enable operation of multiproduct catalytic reactors of the slurry or packed bubble column type; interdependence of operating variables is so complex that a mathematical model is indispensable

Generalized centrality in trees

In 1982, Slater defined path subgraph analogues to the center, median, and (branch or branchweight) centroid of a tree. We define three families of central substructures of trees, including three types of central subtrees of degree at most D that yield the center, median, and centroid for D = 0 and Slater's path analogues for D = 2. We generalize these results concerning paths and include proofs that each type of generalized center and generalized centroid is unique. We also present algorithms for finding one or all generalized central substructures of each type.

Three-phase packed bed reactor with an evaporating solvent—II. Modelling of the reactor

In this paper two models are presented for a three-phase catalytic packed bed reactor in which in evaporating solvent is used to absorb and remove most of the reaction heat. A plug flow model and a model comprising mass and heat dispersion in the reactor are discussed. The results of both models are compared to each other and to experimental data obtained in a miniplant on the hydrogenation of 2,4,6-trinitrotoluene to triaminotoluene described in Part I. The influence of reactor pressure, feed temperature and the molar ratio of hydrogen to the reactant in the feed are discussed. It is concluded that both models can well describe the influence of the operating variables on the reactor behaviour and that a large part of the reaction heat can be removed by evaporation of the solvent. From a comparison with the experimental results it is concluded that the dispersion model can well describe the experimental data for a fresh catalyst. The agreement between the model and the experimental data for a deactivated catalyst is not good. As long as no quantitative description of the local deactivation in the packed bed is available, any model will fail to predict local concentrations in the reactor. Despite this drawback recommendations can be given how to use this reactor type of optimize the selectivity in producing an intermediate product