2,283 research outputs found

    Food Webs: Experts Consuming Families of Experts

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    The question what determines the structure of natural food webs has been listed among the nine most important unanswered questions in ecology. It arises naturally from many problems related to ecosystem stability and resilience. The traditional view is that population-dynamical stability is crucial for understanding the observed structures. But phylogeny (evolutionary history) has also been suggested as the dominant mechanism. Here we show that observed topological features of predatory food webs can be reproduced to unprecedented accuracy by a mechanism taking into account only phylogeny, size constraints, and the heredity of the trophically relevant traits of prey and predators. The analysis reveals a tendency to avoid resource competition rather than apparent competition. In food webs with many parasites this pattern is reversed.Comment: 16 pages, 3 figures, 1 table + Appendix of 36 pages, 18 figures. movie available from http://ag.rossberg.net/matching.mp

    Coelacanths

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    Hadron Physics and Confinement Physics in Lattice QCD

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    We are aiming to construct Quark Hadron Physics and Confinement Physics based on QCD. Using SU(3)c_c lattice QCD, we are investigating the three-quark potential at T=0 and T0T \ne 0, mass spectra of positive and negative-parity baryons in the octet and the decuplet representations of the SU(3) flavor, glueball properties at T=0 and T0T \ne 0. We study also Confinement Physics using lattice QCD. In the maximally abelian (MA) gauge, the off-diagonal gluon amplitude is strongly suppressed, and then the off-diagonal gluon phase shows strong randomness, which leads to a large effective off-diagonal gluon mass, Moff1.2GeVM_{\rm off} \simeq 1.2 {\rm GeV}. Due to the large off-diagonal gluon mass in the MA gauge, infrared QCD is abelianized like nonabelian Higgs theories. In the MA gauge, there appears a macroscopic network of the monopole world-line covering the whole system. From the monopole current, we extract the dual gluon field BμB_\mu, and examine the longitudinal magnetic screening. We obtain mBm_B \simeq 0.5 GeV in the infrared region, which indicates the dual Higgs mechanism by monopole condensation. From infrared abelian dominance and infrared monopole condensation, low-energy QCD in the MA gauge is described with the dual Ginzburg-Landau (DGL) theory.Comment: Invited talk given at International Symposium on Hadrons and Nuclei, Seoul, Korea, 20-22 Feb 200

    Abelianization of QCD in the Maximally Abelian Gauge and the Nambu-'t Hooft Picture for Color Confinement

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    We study the Nambu-'t Hooft picture for color confinement in terms of the abelianization of QCD and monopole condensation in the maximally abelian (MA) gauge. In the MA gauge in the Euclidean metric, the off-diagonal gluon amplitude is strongly suppressed, and then the off-diagonal gluon phase shows strong randomness, which leads to rapid reduction of the off-diagonal gluon correlation. In SU(2) and SU(3) lattice QCD in the MA gauge with the abelian Landau gauge, the Euclidean gluon propagator indicates a large effective mass of the off-diagonal gluon as Moff1GeVM_{\rm off} \simeq 1 {\rm GeV} in the intermediate distance as 0.2fmr0.8fm0.2{\rm fm} \le r \le 0.8{\rm fm}. Due to the infrared inactiveness of off-diagonal gluons, infrared QCD is well abelianized like nonabelian Higgs theories in the MA gauge. We investigate the inter-monopole potential and the dual gluon field BμB_\mu in the MA gauge, and find longitudinal magnetic screening with mBm_B \simeq 0.5 GeV in the infrared region, which indicates the dual Higgs mechanism by monopole condensation. We define the ``gluonic Higgs scalar field'' providing the MA projection, and find the correspondence between its hedgehog singularity and the monopole location in lattice QCD.Comment: Invited talk given at QCD02: High-Energy Physics International Conference in Quantum Chromodynamics, Montpellier, France, 2-9 Jul 200

    Quark Confinement Physics from Quantum Chromodynamics

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    We show the construction of the dual superconducting theory for the confinement mechanism from QCD in the maximally abelian (MA) gauge using the lattice QCD Monte Carlo simulation. We find that essence of infrared abelian dominance is naturally understood with the off-diagonal gluon mass moff1.2GeVm_{\rm off} \simeq 1.2 {\rm GeV} induced by the MA gauge fixing. In the MA gauge, the off-diagonal gluon amplitude is forced to be small, and the off-diagonal gluon phase tends to be random. As the mathematical origin of abelian dominance for confinement, we demonstrate that the strong randomness of the off-diagonal gluon phase leads to abelian dominance for the string tension. In the MA gauge, there appears the macroscopic network of the monopole world-line covering the whole system. We investigate the monopole-current system in the MA gauge by analyzing the dual gluon field BμB_\mu. We evaluate the dual gluon mass as mB=0.4m_B = 0.4 \sim 0.5GeV in the infrared region, which is the lattice-QCD evidence of the dual Higgs mechanism by monopole condensation. Owing to infrared abelian dominance and infrared monopole condensation, QCD in the MA gauge is describable with the dual Ginzburg-Landau theory.Comment: Invited talk given at KEK-Tanashi International Symposium on Physics of Hadrons and Nuclei, Tokyo, Japan, 14-17 Dec 199
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