2,453 research outputs found
Introduction
This chapter provides an overview of the historiography on urban network theory explaining the urban models that influenced the theory. It defines the book’s theme, the urban logistics network, and explains why the theme is relevant by pointing out to several gaps in the literature in three areas: the spatial terminologies and scale, the shapes of networks, and the agency of networks. Four parts of the book (I. Single Gateway, II. Changing Shapes of the Urban Network, III. The Making of the Regional Network, and IV. Using the Network) are explained in the process. The chapter clarifies the book’s aim to provide empirical case studies that can be used as tools for other researchers to model their own urban networks
Mass transfer of carbon dioxide across sea surfaces
The rate of mass transfer of carbon dioxide across the sea surface was investigated in the laboratory and at sea. In the laboratory, radioactive tracer techniques were employed using high specific activity C14O2. The equilibrium distribution of CO2 is not affected greatly and the mass transfer measured is very nearly the exchange coefficient...
Determination of critical current density in melt-processed HTS bulks from levitation force measurements
A simple approach to describe the levitation force measurements on
melt-processed HTS bulks was developed. A couple of methods to determine the
critical current density were introduced. The averaged -plane
values for the field parallel to this plane were determined. The first and
second levitation force hysteresis loops calculated with these values
coincide remarkably well with the experimental data.Comment: 10 pages (tex), 2 figures (in jpeg
Random Hamiltonian in thermal equilibrium
A framework for the investigation of disordered quantum systems in thermal
equilibrium is proposed. The approach is based on a dynamical model--which
consists of a combination of a double-bracket gradient flow and a uniform
Brownian fluctuation--that `equilibrates' the Hamiltonian into a canonical
distribution. The resulting equilibrium state is used to calculate quenched and
annealed averages of quantum observables.Comment: 8 pages, 4 figures. To appear in DICE 2008 conference proceeding
Finite-temperature phase transitions in quasi-one-dimensional molecular conductors
Phase transitions in 1/4-filled quasi-one-dimensional molecular conductors
are studied theoretically on the basis of extended Hubbard chains including
electron-lattice interactions coupled by interchain Coulomb repulsion. We apply
the numerical quantum transfer-matrix method to an effective one-dimensional
model, treating the interchain term within mean-field approximation.
Finite-temperature properties are investigated for the charge ordering, the
"dimer Mott" transition (bond dimerization), and the spin-Peierls transition
(bond tetramerization). A coexistent state of charge order and bond
dimerization exhibiting dielectricity is predicted in a certain parameter
range, even when intrinsic dimerization is absent.Comment: to be published in J. Phys. Soc. Jpn., Vol. 76 (2007) No. 1 (5 pages,
4 figures); typo correcte
On the correllation effect in Peierls-Hubbard chains
We reexamine the dimerization, the charge and the spin gaps of a half-filled
Peierls-Hubbard chain by means of the incremental expansion technique. Our
numerical findings are in significant quantitative conflict with recently
obtained results by M. Sugiura and Y. Suzumura [J. Phys. Soc. Jpn. v. 71 (2002)
697] based on a bosonization and a renormalization group method, especially
with respect to the charge gap. Their approach seems to be valid only in the
weakly correlated case.Comment: 7pages,4figures(6eps-files
Origin and evolution of water oxidation before the last common ancestor of the Cyanobacteria
Photosystem II, the water oxidizing enzyme, altered the course of evolution by filling the atmosphere with oxygen. Here, we reconstruct the origin and evolution of water oxidation at an unprecedented level of detail by studying the phylogeny of all D1 subunits, the main protein coordinating the water oxidizing cluster (Mn4CaO5) of Photosystem II. We show that D1 exists in several forms making well-defined clades, some of which could have evolved before the origin of water oxidation and presenting many atypical characteristics. The most ancient form is found in the genome of Gloeobacter kilaueensis JS-1 and this has a C-terminus with a higher sequence identity to D2 than to any other D1. Two other groups of early evolving D1 correspond to those expressed under prolonged far-red illumination and in darkness. These atypical D1 forms are characterized by a dramatically different Mn4CaO5 binding site and a Photosystem II containing such a site may assemble an unconventional metal cluster. The first D1 forms with a full set of ligands to the Mn4CaO5 cluster are grouped with D1 proteins expressed only under low oxygen concentrations and the latest evolving form is the dominant type of D1 found in all cyanobacteria and plastids. In addition, we show that the plastid ancestor had a D1 more similar to those in early branching Synechococcus. We suggest each one of these forms of D1 originated from transitional forms at different stages towards the innovation and optimization of water oxidation before the last common ancestor of all known cyanobacteria
Finite-Temperature Phase Diagram of Quasi-One-Dimensional Molecular Conductors: Quantum Monte Carlo Study
Finite-temperature phase transitions in quasi-one-dimensional quarter-filled
systems are investigated by the extended Hubbard model with electron-lattice
coupling. Using a quantum Monte Carlo method combined with the inter-chain
mean-field approximation, we clarify competing and coexisting behaviors among
charge ordering, dimer Mott, and spin-Peierls states. It is pointed out that an
anharmonicity of lattice distortions plays an important role in multi-critical
behaviors. The results are compared with experimental data for
quasi-one-dimensional molecular conductors such as DCNQI and TMTTF compounds.Comment: Corrected typo
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