545 research outputs found
Hot Spots and Pseudogaps for Hole- and Electron-Doped High-Temperature Superconductors
Using cluster perturbation theory, it is shown that the spectral weight and
pseudogap observed at the Fermi energy in recent Angle Resolved Photoemission
Spectroscopy (ARPES) of both electron and hole-doped high-temperature
superconductors find their natural explanation within the t-t'-t''-U Hubbard
model in two dimensions. The value of the interaction U needed to explain the
experiments for electron-doped systems at optimal doping is in the weak to
intermediate coupling regime where the t-J model is inappropriate. At strong
coupling, short-range correlations suffice to create a pseudogap but at weak
coupling long correlation lengths associated with the antiferromagnetic wave
vector are necessary.Comment: RevTeX 4, 4 pages, 5 figures (2 in color
Strong-Coupling Perturbation Theory of the Hubbard Model
The strong-coupling perturbation theory of the Hubbard model is presented and
carried out to order (t/U)^5 for the one-particle Green function in arbitrary
dimension. The spectral weight A(k,omega) is expressed as a Jacobi continued
fraction and compared with new Monte-Carlo data of the one-dimensional,
half-filled Hubbard model. Different regimes (insulator, conductor and
short-range antiferromagnet) are identified in the temperature--hopping
integral (T,t) plane. This work completes a first paper on the subject (Phys.
Rev. Lett. 80, 5389 (1998)) by providing details on diagrammatic rules and
higher-order results. In addition, the non half-filled case, infinite
resummations of diagrams and the double occupancy are discussed. Various tests
of the method are also presented.Comment: 28 pages, 19 figure
Symmetry properties of Penrose type tilings
The Penrose tiling is directly related to the atomic structure of certain
decagonal quasicrystals and, despite its aperiodicity, is highly symmetric. It
is known that the numbers 1, , , , ..., where
, are scaling factors of the Penrose tiling. We show that
the set of scaling factors is much larger, and for most of them the number of
the corresponding inflation centers is infinite.Comment: Paper submitted to Phil. Mag. (for Proceedings of Quasicrystals: The
Silver Jubilee, Tel Aviv, 14-19 October, 2007
Greenhouse Gas Emissions and Fire Behavior Impacts Following California Fuel Treatments
Fuel treatments are being increasingly applied across California landscapes as communities struggle to recover from wildfire disasters nationwide. Increased funding for treatments stems from grants under CARB’s Greenhouse Gas Reduction Fund and funding requires reports accounting the yielded benefits from these fuel treatments. Using data from real-world local scale fuel treatments, I used the forest simulation model FVSFEE and fire behavior software IFTDSS to quantify GHG emission benefits and fire behavior impacts 70 years after treatment. Results suggest that fuel treatments do not yield significant GHG benefits, and fire behavior impacts (conditional flame length) are minimal but overall show slight reductions in the impact area’s burn severity. However, treatment outcomes may vary on the localized landscapes, size of treatment, and unique parameters applied to each treatment simulation
Topological Equivalence between the Fibonacci Quasicrystal and the Harper Model
One-dimensional quasiperiodic systems, such as the Harper model and the
Fibonacci quasicrystal, have long been the focus of extensive theoretical and
experimental research. Recently, the Harper model was found to be topologically
nontrivial. Here, we derive a general model that embodies a continuous
deformation between these seemingly unrelated models. We show that this
deformation does not close any bulk gaps, and thus prove that these models are
in fact topologically equivalent. Remarkably, they are equivalent regardless of
whether the quasiperiodicity appears as an on-site or hopping modulation. This
proves that these different models share the same boundary phenomena and
explains past measurements. We generalize this equivalence to any
Fibonacci-like quasicrystal, i.e., a cut and project in any irrational angle.Comment: 7 pages, 2 figures, minor change
Interacting two helical edge modes in quantum spin Hall systems
We study theoretically the two interacting one-dimensional helical modes at
the edges of the quantum spin Hall systems. A new type of inter-edge correlated
liquid (IECL) without the spin gap is found. This liquid shows the diverging
density wave (DW) and superconductivity (SC) correlations much stronger than
those of the spinfull electrons. Possible experimental observations are also
discussed
Integrable lattices and their sublattices II. From the B-quadrilateral lattice to the self-adjoint schemes on the triangular and the honeycomb lattices
An integrable self-adjoint 7-point scheme on the triangular lattice and an
integrable self-adjoint scheme on the honeycomb lattice are studied using the
sublattice approach. The star-triangle relation between these systems is
introduced, and the Darboux transformations for both linear problems from the
Moutard transformation of the B-(Moutard) quadrilateral lattice are obtained. A
geometric interpretation of the Laplace transformations of the self-adjoint
7-point scheme is given and the corresponding novel integrable discrete 3D
system is constructed.Comment: 15 pages, 6 figures; references added, some typos correcte
BIOREFINERIES USING AGRICULTURAL RESIDUE FEEDSTOCK IN THE GREAT PLAINS
Rising prices and uncertain supplies of petroleum, together with environmental concerns regarding fossil fuel combustion, has enhanced interest in biobased products and fuels. The work reported here analyzes the feasibility of a multi-product biorefinery using wheat straw as feedstock that produces ethanol, electricity, and cellulose nanofibers. The nanofibers (nanowhiskers) would be used as reinforcements in a biobased nanocomposite material that could substitute for fiberglass in many applications. The analysis indicates that, at 2005 prices and costs, the biorefinery would be marginally profitable. Anticipated advances in bioprocessing technology would enhance profitability. The facility would also make a substantial contribution to the biorefinery site area economy, as a high percentage of operating expenses would be payments to local entities. The growth of a biobased industry could have major economic development implications for the Great Plains/Midwest region.biomass, biomaterials, ethanol, wheat straw, cellulose nanowhiskers (CNW), economic development, Resource /Energy Economics and Policy,
Use of Agricultural Residue Feedstock In North Dakota Biorefineries
Rising prices and uncertain supplies of petroleum, together with environmental concerns regarding fossil fuel combustion, have enhanced interest in biobased products and fuels. This study analyzes the feasibility of a multi-product biorefinery that uses wheat straw as feedstock to produce ethanol, electricity, and cellulose nanofibers. Nanofibers (nanowhiskers) would be used as reinforcements in a biobased nanocomposite material that could substitute for fiberglass in many applications. The growth of a biobased industry could have major economic development implications for the Great Plains/Midwest region.biomass, biomaterials, cellulose nanofibers (CNFs), economic development, ethanol, wheat straw, Agribusiness, Resource /Energy Economics and Policy,
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