103,008 research outputs found

    Size structure and inequality in a commercial stand of the seaweed gelidium-sesquipedale

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    The temporal dynamics of the frequency distributions of 2 measures of Gelidium sesquipedale frond size, length and weight, was investigated in a subtidal stand under commercial exploitation. Frond weight/length allometry was highly variable, both seasonally and between years, showing that in this species weight and length cannot be used interchangeably as a measure of frond size. Physical disturbances played a fundamental role in allometric variability. The loss of branches due to commercial harvest and storms reduced the slope of the log weight/log length relationship. During spring the slope increased, indicating the production and growth of lateral branches. Size differences among individuals in the population (inequality) were quantified by 3 statistics: the skewness coefficient (g(1)), the coefficient of variation (CV), and the Gini coefficient (G). Highly significant changes in frond length inequality, but not weight, were shown. These correspond to periods when G. sesquipedale length structure varied due to the combined effects of the demographic parameters that regulate the population (frond recruitment, survival, breakage and growth). Graphical analysis of significantly different length structures revealed that a recruitment peak of vegetatively developed fronds occurred during winter, following periods of high frond mortality and breakage caused by both human (summer harvesting) and natural (late fall storms) disturbances. During late spring and summer, the density of smaller fronds decreased due to mortality and growth into higher size classes. To assess density-dependent regulation processes, such as suppressed growth of smaller fronds and self-thinning, the time variation of both relationships, inequality/mean frond weight and biomass/density, was analysed. Inequality/mean frond weight and biomass/density values decreased from summer to winter and increased to the following summer. The increase of inequality while mean frond weight is increasing is consistent with the asymmetric competition theory on the development of crowded plant stands, and supports the hypothesis that the slower growth of smaller fronds during this period (Santos 1994; Mar. Ecol. Prog. Ser. 107: 295-305) is due to intraspecific competition. The time trajectory of the biomass/density relationship is perpendicular to and lies above the theoretical self-thinning line. Evidence for self-thinning was thus not detected. A conceptual model for the functioning of this population is proposed. Thinning and frond breakage caused by disturbances might be keeping intraspecific competition in these G. sesquipedale crowded stands (up to 18 000 fronds m(-2)) at low levels.info:eu-repo/semantics/publishedVersio

    Experimental Signatures of Fermiophobic Higgs bosons

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    The most general Two Higgs Doublet Model potential without explicit CP violation depends on 10 real independent parameters. Excluding spontaneous CP violation results in two 7 parameter models. Although both models give rise to 5 scalar particles and 2 mixing angles, the resulting phenomenology of the scalar sectors is different. If flavour changing neutral currents at tree level are to be avoided, one has, in both cases, four alternative ways of introducing the fermion couplings. In one of these models the mixing angle of the CP even sector can be chosen in such a way that the fermion couplings to the lightest scalar Higgs boson vanishes. At the same time it is possible to suppress the fermion couplings to the charged and pseudo-scalar Higgs bosons by appropriately choosing the mixing angle of the CP odd sector. We investigate the phenomenology of both models in the fermiophobic limit and present the different branching ratios for the decays of the scalar particles. We use the present experimental results from the LEP collider to constrain the models.Comment: 23 pages, 18 figures included, newer experimental data include

    Hamilton-Jacobi Approach for Power-Law Potentials

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    The classical and relativistic Hamilton-Jacobi approach is applied to the one-dimensional homogeneous potential, V(q)=αqnV(q)=\alpha q^n, where α\alpha and nn are continuously varying parameters. In the non-relativistic case, the exact analytical solution is determined in terms of α\alpha, nn and the total energy EE. It is also shown that the non-linear equation of motion can be linearized by constructing a hypergeometric differential equation for the inverse problem t(q)t(q). A variable transformation reducing the general problem to that one of a particle subjected to a linear force is also established. For any value of nn, it leads to a simple harmonic oscillator if E>0E>0, an "anti-oscillator" if E<0E<0, or a free particle if E=0. However, such a reduction is not possible in the relativistic case. For a bounded relativistic motion, the first order correction to the period is determined for any value of nn. For n>>1n >> 1, it is found that the correction is just twice that one deduced for the simple harmonic oscillator (n=2n=2), and does not depend on the specific value of nn.Comment: 12 pages, Late
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