134,494 research outputs found
Physics of the Pseudogap State: Spin-Charge Locking
The properties of the pseudogap phase above Tc of the high-Tc cuprate
superconductors are described by showing that the Anderson-Nambu SU(2) spinors
of an RVB spin gap 'lock' to those of the electron charge system because of the
resulting improvement of kinetic energy. This enormously extends the range of
the vortex liquid state in these materials. As a result it is not clear that
the spinons are ever truly deconfined. A heuristic description of the
electrodynamics of this pseudogap-vortex liquid state is proposed.Comment: Submitted to Phys Rev Letter
Case study: design, operation and water quality management of a combined wet and dry pond system
Pond structures as cost-effective water treatment, storage and “source control” drainage techniques can be applied in order to reduce wastewater treatment costs, produce water for subsequent recycling and reduce the risk of downstream flooding. However, there is a need for detailed
design, operation and maintenance data. The purpose of this study was to optimise design and operation guidelines, and to assess the water treatment potential of stormwater
pond systems. Performance data (15 months) for a stormwater pond pilot plant were collected. The system is based on a combined silt trap, attenuation wet pond and dry pond system
applied for drainage of roof water run-off from a single domestic property. United Kingdom Building Research Establishment and Construction Industry Research and Information Association, and German Association for Water, Wastewater and Waste design guidelines were tested. These design guidelines were insufficient because they do not consider local hydrological and soil conditions. The infiltration function for the dry pond is logarithmic and depends on the season. Furthermore, biochemical and physical algal control techniques were successfully applied, and passive water treatment of rainwater run-off with a wet pond was found to be sufficient. However, seasonal and diurnal variations of biochemical oxygen demand, dissolved oxygen and pH were recorded. Finally, capital and labour costs for small ponds are high
Sun-synchronous highly elliptical orbits using low-thrust propulsion
Due to restrictions within the current architecture of the global observing system (GOS), space-based remote sensing of Earth suffers from an acute data-deficit over the critical polar-regions. Currently, observation of high-latitude regions is conducted using composite images from spacecraft in geostationary (GEO) and low-Earth orbits (LEOs) [1]. However, the oblique viewing geometry from GEO-based systems to latitudes above around 55 deg [2] and the insufficient temporal resolution of spacecraft in LEO means there is currently no source of continuous imagery for polar-regions obtained with a data refresh rate of less than 15 minutes, as is typically available elsewhere for meteorological observations
Symmetry reduction in group 4mm photonic crystals
The size of absolute band gaps in two-dimensional photonic crystals is often limited by band degeneracies at the lattice symmetry points. By reducing the lattice symmetry, these degeneracies can be lifted to increase the size of existing photonic band gaps, or to create new gaps where none existed for the more symmetric structure. Specifically, symmetry reduction by the addition of different diameter rods into the unit cell of two-dimensional square lattices (Laue group 4mm) is explored. This approach is especially useful in opening absolute band gaps in structures of dielectric rods in air, which are more easily microfabricated than a crystal of air columns in a dielectric background. Symmetry reduction offers a rational approach for exploring and designing new photonic crystal structures
Larger Two-Dimensional Photonic Band Gaps
Absolute photonic band gaps in two-dimensional square and honeycomb lattices of circular cross-section rods can be increased by reducing the structure symmetry. The addition of a smaller diameter rod into the center of each lattice unit cell lifts band degeneracies to create significantly larger band gaps. Symmetry breaking is most effective at filling fractions near those which produce absolute band gaps for the original lattice. Rod diameter ratios in the range 0.1–0.2 yield the greatest improvement in absolute gap size. Crystal symmetry reduction opens up new ways for engineering photonic gaps
Spontaneous superconductivity and optical properties of high-Tc cuprates
We suggest that the high temperature superconductivity in cuprate compounds
may emerge due to interaction between copper-oxygen layers mediated by in-plane
plasmons. The strength of the interaction is determined by the c-axis geometry
and by the ab-plane optical properties. Without making reference to any
particular in-plane mechanism of superconductivity, we show that the interlayer
interaction favors spontaneous appearance of the superconductivity in the
layers. At a qualitative level the model describes correctly the dependence of
the transition temperature on the interlayer distance, and on the number of
adjacent layers in multilayered homologous compounds. Moreover, the model has a
potential to explain (i) a mismatch between the optimal doping levels for
critical temperature and superconducting density and (ii) a universal scaling
relation between the dc-conductivity, the superfluid density, and the
superconducting transition temperature.Comment: 4.4 pages, 2 figures; v2 matches the published version (clarifying
remarks and references are added
The BSSN formulation is a partially constrained evolution system
Relativistic simulations in 3+1 dimensions typically monitor the Hamiltonian
and momentum constraints during evolution, with significant violations of these
constraints indicating the presence of instabilities. In this paper we rewrite
the momentum constraints as first-order evolution equations, and show that the
popular BSSN formulation of the Einstein equations explicitly uses the momentum
constraints as evolution equations. We conjecture that this feature is a key
reason for the relative success of the BSSN formulation in numerical
relativity.Comment: 8 pages, minor grammatical correction
The isotope effect in the Hubbard model with local phonons
The isotope effect (IE) in the two-dimensional Hubbard model with Holstein
phonons is studied using the dynamical cluster approximation with quantum Monte
Carlo. At small electron-phonon (EP) coupling the IE is negligible. For larger
EP coupling there is a large and positive IE on the superconducting temperature
that decreases with increasing doping. A significant IE also appears in the
low-energy density of states, kinetic energy and charge excitation spectrum. A
negligible IE is found in the pseudogap and antiferromagnetic (AF) properties
at small doping whereas the AF susceptibility at intermediate doping increases
with decreasing phonon frequency . This IE stems from increased
polaronic effects with decreasing . A larger IE at smaller doping
occurs due to stronger polaronic effects determined by the interplay of the EP
interaction with stronger AF correlations. The IE of the Hubbard-Holstein model
exhibits many similarities with the IE measured in cuprate superconductors
Superposition Formulas for Darboux Integrable Exterior Differential Systems
In this paper we present a far-reaching generalization of E. Vessiot's
analysis of the Darboux integrable partial differential equations in one
dependent and two independent variables. Our approach provides new insights
into this classical method, uncovers the fundamental geometric invariants of
Darboux integrable systems, and provides for systematic, algorithmic
integration of such systems. This work is formulated within the general
framework of Pfaffian exterior differential systems and, as such, has
applications well beyond those currently found in the literature. In
particular, our integration method is applicable to systems of hyperbolic PDE
such as the Toda lattice equations, 2 dimensional wave maps and systems of
overdetermined PDE.Comment: 80 page report. Updated version with some new sections, and major
improvements to other
Shuttle electrical environment
Part of an AFGL payload flown on the STS-4 mission consisted of experiments to measure in-situ electric fields, electron densities, and vehicle charging. During this flight some 11 hours of data were acquired ranging from 5 minute snapshots up to continuous half-orbits. These experiments are described and results presented for such vehicle induced events as a main engine burn, thruster firings and water dumps in addition to undisturbed periods. The main characteristic of all the vehicle induced events is shown to be an enhancement in the low frequency noise (less than 2 kHz), in both the electrostatic and electron irregularity (delta N/N) spectra. The non-event results indicate that the electrostatic broadband emissions show a white noise characteristic in the low frequency range up to 2 kHz at an amplitude of 10 db above the shuttle design specification limit, falling below that limit above 10 kHz. The vehicle potential remained within the range of -3 to +1 volt throughout the flight which exhibits normal behavior for a satellite in a low equatorial orbit
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