617 research outputs found

    A note on the diet and feeding selectivity of juvenile riverbream, Acanthopagrus berda (Forskal, 1775), in a subtropical mangrove creek

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    The diet and food selectivity of juvenile (< 100 mm S.L.) Acanthopagrus berda were investigated in Beachwood creek, north of Durban. Fish and benthic samples were taken from November 1986 to September 1987. The diet of juvenile A. berda was varied but crustaceans, mainly amphipods, were the dominant prey item. Ivlev's (1961) electivity index revealed a positive selection for amphipods, tanaids and fish scales

    Jarlskog Invariant of the Neutrino Mapping Matrix

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    The Jarlskog Invariant Jν−mapJ_{\nu-map} of the neutrino mapping matrix is calculated based on a phenomenological model which relates the smallness of light lepton masses mem_e and m1m_1 (of ν1\nu_1) with the smallness of TT violation. For small TT violating phase χl\chi_l in the lepton sector, Jν−mapJ_{\nu-map} is proportional to χl\chi_l, but mem_e and m1m_1 are proportional to χl2\chi_l^2. This leads to Jν−map≅1/6memμ+O(memμmτ2)+O(m1m2m32) J_{\nu-map} \cong {1/6}\sqrt{\frac{m_e}{m_\mu}}+O \bigg(\sqrt{\frac{m_em_\mu}{m_\tau^2}}\bigg)+O \bigg(\sqrt{\frac{m_1m_2}{m_3^2}}\bigg). Assuming m1m2m32<<memμ\sqrt{\frac{m_1m_2}{m_3^2}}<<\sqrt{\frac{m_e}{m_\mu}}, we find Jν−map≅1.16×10−2J_{\nu-map}\cong 1.16\times 10^{-2}, consistent with the present experimental data.Comment: 19 page

    Composition, distribution and abundance of ichthyoplankton in the Sundays River Estuary

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    The species composition, distribution and seasonal abundance of ichthyoplankton in the Sundays River estuary was investigated at five stations from March 1986 to March 1987. Two estuarine taxa, the clupeid Gilchristella aestuaria and gobies Caffrogobius spp., accounted for 86% of the ichthyoplankton community, while the marine Mugilidae and sparid Rhabdosargus holubi together comprised 12% of the total catch. Ichthyoplankton densities were highest in the middle and upper reaches of the estuary where zooplankton stocks were greatest. Juvenile G. aestuaria predominated in the bottom waters throughout the system but the larvae were more evenly distributed (vertically) within the water column. In contrast, the mugilids were concentrated in surface waters throughout the estuary. Larvae were most abundant during spring and summer months, coinciding with the documented spawning period of most species and the peak in zooplankton biomass

    Evidence for the Gompertz Curve in the Income Distribution of Brazil 1978-2005

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    This work presents an empirical study of the evolution of the personal income distribution in Brazil. Yearly samples available from 1978 to 2005 were studied and evidence was found that the complementary cumulative distribution of personal income for 99% of the economically less favorable population is well represented by a Gompertz curve of the form G(x)=exp⁡[exp⁡(A−Bx)]G(x)=\exp [\exp (A-Bx)], where xx is the normalized individual income. The complementary cumulative distribution of the remaining 1% richest part of the population is well represented by a Pareto power law distribution P(x)=βx−αP(x)= \beta x^{-\alpha}. This result means that similarly to other countries, Brazil's income distribution is characterized by a well defined two class system. The parameters AA, BB, α\alpha, β\beta were determined by a mixture of boundary conditions, normalization and fitting methods for every year in the time span of this study. Since the Gompertz curve is characteristic of growth models, its presence here suggests that these patterns in income distribution could be a consequence of the growth dynamics of the underlying economic system. In addition, we found out that the percentage share of both the Gompertzian and Paretian components relative to the total income shows an approximate cycling pattern with periods of about 4 years and whose maximum and minimum peaks in each component alternate at about every 2 years. This finding suggests that the growth dynamics of Brazil's economic system might possibly follow a Goodwin-type class model dynamics based on the application of the Lotka-Volterra equation to economic growth and cycle.Comment: 22 pages, 15 figures, 4 tables. LaTeX. Accepted for publication in "The European Physical Journal B

    Particle-Like Description in Quintessential Cosmology

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    Assuming equation of state for quintessential matter: p=w(z)ρp=w(z)\rho, we analyse dynamical behaviour of the scale factor in FRW cosmologies. It is shown that its dynamics is formally equivalent to that of a classical particle under the action of 1D potential V(a)V(a). It is shown that Hamiltonian method can be easily implemented to obtain a classification of all cosmological solutions in the phase space as well as in the configurational space. Examples taken from modern cosmology illustrate the effectiveness of the presented approach. Advantages of representing dynamics as a 1D Hamiltonian flow, in the analysis of acceleration and horizon problems, are presented. The inverse problem of reconstructing the Hamiltonian dynamics (i.e. potential function) from the luminosity distance function dL(z)d_{L}(z) for supernovae is also considered.Comment: 35 pages, 26 figures, RevTeX4, some applications of our treatment to investigation of quintessence models were adde

    Individual isotopic specializations predict subsequent inter-individual variation in movement in a freshwater fish

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    Despite many similarities and intuitive links between individual dietary specialization and behavioral inter-individual variation, these phenomena have been studied in isolation, and empirical data confirming relationships between these intraspecific variance sources are lacking. Here we use stable isotope analysis and acoustic telemetry to test the hypothesis that individual specialization in trophic (d15N) and littoral/pelagic prey reliance (d13C) covary with inter-individual variation in movement in a group of 34 free-swimming burbot (Lota lota). By performing stable isotope analysis on tissues with differing isotopic turnover rates (anal fin and dorsal muscle), in 24 lethally sampled burbot, we demonstrate that individual specialization in trophic niche (d15N) and li

    The Importance of Time Congruity in the Organisation.

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    In 1991 Kaufman, Lane, and Lindquist proposed that time congruity in terms of an individual's time preferences and the time use methods of an organisation would lead to satisfactory performance and enhancement of quality of work and general life. The research reported here presents a study which uses commensurate person and job measures of time personality in an organisational setting to assess the effects of time congruity on one aspect of work life, job-related affective well-being. Results show that time personality and time congruity were found to have direct effects on well-being and the influence of time congruity was found to be mediated through time personality, thus contributing to the person–job (P–J) fit literature which suggests that direct effects are often more important than indirect effects. The study also provides some practical examples of ways to address some of the previously cited methodological issues in P–J fit research

    Cosmology at the Millennium

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    One hundred years ago we did not know how stars generate energy, the age of the Universe was thought to be only millions of years, and our Milky Way galaxy was the only galaxy known. Today, we know that we live in an evolving and expanding Universe comprising billions of galaxies, all held together by dark matter. With the hot big-bang model, we can trace the evolution of the Universe from the hot soup of quarks and leptons that existed a fraction of a second after the beginning to the formation of galaxies a few billion years later, and finally to the Universe we see today 13 billion years after the big bang, with its clusters of galaxies, superclusters, voids, and great walls. The attractive force of gravity acting on tiny primeval inhomogeneities in the distribution of matter gave rise to all the structure seen today. A paradigm based upon deep connections between cosmology and elementary particle physics -- inflation + cold dark matter -- holds the promise of extending our understanding to an even more fundamental level and much earlier times, as well as shedding light on the unification of the forces and particles of nature. As we enter the 21st century, a flood of observations is testing this paradigm.Comment: 44 pages LaTeX with 14 eps figures. To be published in the Centennial Volume of Reviews of Modern Physic

    Group diversity and group identification:the moderating role of diversity beliefs

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    Research on diversity in teams and organizations has revealed ambiguous results regarding the effects of group composition on workgroup performance. The categorization—elaboration model (van Knippenberg et al., 2004) accounts for this variety and proposes two different underlying processes. On the one hand diversity may bring about intergroup bias which leads to less group identification, which in turn is followed by more conflict and decreased workgroup performance. On the other hand, the information processing approach proposes positive effects of diversity because of a more elaborate processing of information brought about by a wider pool and variety of perspectives in more diverse groups. We propose that the former process is contingent on individual team members' beliefs that diversity is good or bad for achieving the team's aims. We predict that the relationship between subjective diversity and identification is more positive in ethnically diverse project teams when group members hold beliefs that are pro-diversity. Results of two longitudinal studies involving postgraduate students working in project teams confirm this hypothesis. Analyses further reveal that group identification is positively related to students' desire to stay in their groups and to their information elaboration. Finally, we found evidence for the expected moderated mediation model with indirect effects of subjective diversity on elaboration and the desire to stay, mediated through group identification, moderated by diversity beliefs
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