2,151 research outputs found
Giant strongly connected component of directed networks
We describe how to calculate the sizes of all giant connected components of a
directed graph, including the {\em strongly} connected one. Just to the class
of directed networks, in particular, belongs the World Wide Web. The results
are obtained for graphs with statistically uncorrelated vertices and an
arbitrary joint in,out-degree distribution . We show that if
does not factorize, the relative size of the giant strongly
connected component deviates from the product of the relative sizes of the
giant in- and out-components. The calculations of the relative sizes of all the
giant components are demonstrated using the simplest examples. We explain that
the giant strongly connected component may be less resilient to random damage
than the giant weakly connected one.Comment: 4 pages revtex, 4 figure
Linear Response Calculations of Spin Fluctuations
A variational formulation of the time--dependent linear response based on the
Sternheimer method is developed in order to make practical ab initio
calculations of dynamical spin susceptibilities of solids. Using gradient
density functional and a muffin-tin-orbital representation, the efficiency of
the approach is demonstrated by applications to selected magnetic and strongly
paramagnetic metals. The results are found to be consistent with experiment and
are compared with previous theoretical calculations.Comment: 11 pages, RevTex; 3 Figures, postscript, high-resolution printing
(~1200dpi) is desire
Quasiparticle band structure of infinite hydrogen fluoride and hydrogen chloride chains
We study the quasiparticle band structure of isolated, infinite HF and HCl
bent (zigzag) chains and examine the effect of the crystal field on the energy
levels of the constituent monomers. The chains are one of the simplest but
realistic models of the corresponding three-dimensional crystalline solids. To
describe the isolated monomers and the chains, we set out from the Hartree-Fock
approximation, harnessing the advanced Green's function methods "local
molecular orbital algebraic diagrammatic construction" (ADC) scheme and "local
crystal orbital ADC" (CO-ADC) in a strict second order approximation, ADC(2,2)
and CO-ADC(2,2), respectively, to account for electron correlations. The
configuration space of the periodic correlation calculations is found to
converge rapidly only requiring nearest-neighbor contributions to be regarded.
Although electron correlations cause a pronounced shift of the quasiparticle
band structure of the chains with respect to the Hartree-Fock result, the
bandwidth essentially remains unaltered in contrast to, e.g., covalently bound
compounds.Comment: 11 pages, 6 figures, 6 tables, RevTeX4, corrected typoe
Carbon Sequestration And Sediment Accretion In San Francisco Bay Tidal Wetlands
Tidal wetlands play an important role with respect to climate change because of both their sensitivity to sea-level rise and their ability to sequester carbon dioxide from the atmosphere. Policy-based interest in carbon sequestration has increased recently, and wetland restoration projects have potential for carbon credits through soil carbon sequestration. We measured sediment accretion, mineral and organic matter accumulation, and carbon sequestration rates using 137Cs and 210Pb downcore distributions at six natural tidal wetlands in the San Francisco Bay Estuary. The accretion rates were, in general, 0.2–0.5 cm year−1, indicating that local wetlands are keeping pace with recent rates of sea-level rise. Mineral accumulation rates were higher in salt marshes and at low-marsh stations within individual sites. The average carbon sequestration rate based on 210Pb dating was 79 g C m−2 year−1, with slightly higher rates based on 137Cs dating. There was little difference in the sequestration rates among sites or across stations within sites, indicating that a single carbon sequestration rate could be used for crediting tidal wetland restoration projects within the Estuary
Chern-Simons matrix model: coherent states and relation to Laughlin wavefunctions
Using a coherent state representation we derive many-body probability
distributions and wavefunctions for the Chern-Simons matrix model proposed by
Polychronakos and compare them to the Laughlin ones. We analyze two different
coherent state representations, corresponding to different choices for electron
coordinate bases. In both cases we find that the resulting probability
distributions do not quite agree with the Laughlin ones. There is agreement on
the long distance behavior, but the short distance behavior is different.Comment: 15 pages, LaTeX; one reference added, abstract and section 5
expanded, typos correcte
A priori Wannier functions from modified Hartree-Fock and Kohn-Sham equations
The Hartree-Fock equations are modified to directly yield Wannier functions
following a proposal of Shukla et al. [Chem. Phys. Lett. 262, 213-218 (1996)].
This approach circumvents the a posteriori application of the Wannier
transformation to Bloch functions. I give a novel and rigorous derivation of
the relevant equations by introducing an orthogonalizing potential to ensure
the orthogonality among the resulting functions. The properties of these,
so-called a priori Wannier functions, are analyzed and the relation of the
modified Hartree-Fock equations to the conventional, Bloch-function-based
equations is elucidated. It is pointed out that the modified equations offer a
different route to maximally localized Wannier functions. Their computational
solution is found to involve an effort that is comparable to the effort for the
solution of the conventional equations. Above all, I show how a priori Wannier
functions can be obtained by a modification of the Kohn-Sham equations of
density-functional theory.Comment: 7 pages, RevTeX4, revise
Red clover necrotic mosaic virus replication proteins accumulate at the endoplasmic reticulum
AbstractRed clover necrotic mosaic virus (RCNMV) encodes N-terminally overlapping proteins of 27 and 88 kDa (p27 and p88) known to be required for replication. Green fluorescent protein (GFP) fusions were used to visualize the location of p27 and p88 within Nicotiana benthamiana cells. GFP:p27 fusions localized to the endoplasmic reticulum (ER), co-localized with ER-targeted yellow fluorescent protein and caused membrane restructuring and proliferation. Cellular fractionation of virus-inoculated N. benthamiana leaves confirmed the association of p27 with ER membranes. GFP:p88 fusions also localized to the ER and co-localized with GFP:p27. Both fusion proteins co-localize to the cortical and cytoplasmic ER and were associated with invaginations of the nuclear envelope. Independent accumulation in, and perturbation of, the ER suggests that p27 and p88 function together in the replication complex. This is the first report of a member of the Tombusviridae replicating in association with the ER
Ising Model on Networks with an Arbitrary Distribution of Connections
We find the exact critical temperature of the nearest-neighbor
ferromagnetic Ising model on an `equilibrium' random graph with an arbitrary
degree distribution . We observe an anomalous behavior of the
magnetization, magnetic susceptibility and specific heat, when is
fat-tailed, or, loosely speaking, when the fourth moment of the distribution
diverges in infinite networks. When the second moment becomes divergent,
approaches infinity, the phase transition is of infinite order, and size effect
is anomalously strong.Comment: 5 page
Lattice Discretization in Quantum Scattering
The utility of lattice discretization technique is demonstrated for solving
nonrelativistic quantum scattering problems and specially for the treatment of
ultraviolet divergences in these problems with some potentials singular at the
origin in two and three space dimensions. This shows that lattice
discretization technique could be a useful tool for the numerical solution of
scattering problems in general. The approach is illustrated in the case of the
Dirac delta function potential.Comment: 9 page
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