5,917 research outputs found
Electronic Structure of Electron-doped Sm1.86Ce0.14CuO4: Strong `Pseudo-Gap' Effects, Nodeless Gap and Signatures of Short Range Order
Angle resolved photoemission (ARPES) data from the electron doped cuprate
superconductor SmCeCuO shows a much stronger pseudo-gap
or "hot-spot" effect than that observed in other optimally doped -type
cuprates. Importantly, these effects are strong enough to drive the
zone-diagonal states below the chemical potential, implying that d-wave
superconductivity in this compound would be of a novel "nodeless" gap variety.
The gross features of the Fermi surface topology and low energy electronic
structure are found to be well described by reconstruction of bands by a
order. Comparison of the ARPES and optical data from
the sample shows that the pseudo-gap energy observed in optical data is
consistent with the inter-band transition energy of the model, allowing us to
have a unified picture of pseudo-gap effects. However, the high energy
electronic structure is found to be inconsistent with such a scenario. We show
that a number of these model inconsistencies can be resolved by considering a
short range ordering or inhomogeneous state.Comment: 5 pages, 4 figure
Stationary untrapped boundary conditions in general relativity
A class of boundary conditions for canonical general relativity are proposed
and studied at the quasi-local level. It is shown that for untrapped or
marginal surfaces, fixing the area element on the 2-surface (rather than the
induced 2-metric) and the angular momentum surface density is enough to have a
functionally differentiable Hamiltonian, thus providing definition of conserved
quantities for the quasi-local regions. If on the boundary the evolution vector
normal to the 2-surface is chosen to be proportional to the dual expansion
vector, we obtain a generalization of the Hawking energy associated with a
generalized Kodama vector. This vector plays the role for the stationary
untrapped boundary conditions which the stationary Killing vector plays for
stationary black holes. When the dual expansion vector is null, the boundary
conditions reduce to the ones given by the non-expanding horizons and the null
trapping horizons.Comment: 11 pages, improved discussion section, a reference added, accepted
for publication in Classical and Quantum Gravit
Estimating Carbon Dynamics in an Intact Lowland Mixed Dipterocarp Forest Using a Forest Carbon Model
Intact dipterocarp forests in Asia act as crucial carbon (C) reservoirs, and it is therefore important to investigate the C dynamics in these forests. We estimated C dynamics, together with net ecosystem production (NEP), in an intact tropical dipterocarp forest of Brunei Darussalam. Fifty-four simulation units (plots; 20 m × 20 m) were established and initial C stocks were determined via direct field measurement. The C dynamics were annually simulated with a regression model and the Forest Biomass and Dead organic matter Carbon (FBDC) model. The initial C stock (Mg C·ha−1) of biomass, litter, dead wood and mineral soil were 213.1 ± 104.8, 2.0 ± 0.8, 31.3 ± 38.8, and 80.7 ± 15.5, respectively. Their annual changes (Mg C·ha−1·year−1) were 3.2 ± 1.1, 0.2 ± 0.2, −3.7 ± 6.1, and −0.3 ± 1.1, respectively. NEP was −0.6 ± 6.1 Mg C·ha−1·year−1, showing large heterogeneity among the plots. The initial C stocks of biomass and dead wood, biomass turnover rates and dead wood decay rates were elucidated as dominant factors determining NEP in a sensitivity analysis. Accordingly, investigation on those input data can constrain an uncertainty in determining NEP in the intact tropical forests
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Receptor interacting protein kinase mediates necrotic cone but not rod cell death in a mouse model of inherited degeneration
Retinitis pigmentosa comprises a group of inherited retinal photoreceptor degenerations that lead to progressive loss of vision. Although in most cases rods, but not cones, harbor the deleterious gene mutations, cones do die in this disease, usually after the main phase of rod cell loss. Rod photoreceptor death is characterized by apoptotic features. In contrast, the mechanisms and features of subsequent nonautonomous cone cell death remain largely unknown. In this study, we show that receptor-interacting protein (RIP) kinase mediates necrotic cone cell death in rd10 mice, a mouse model of retinitis pigmentosa caused by a mutation in a rod-specific gene. The expression of RIP3, a key regulator of programmed necrosis, was elevated in rd10 mouse retinas in the phase of cone but not rod degeneration. Although rd10 mice lacking Rip3 developed comparable rod degeneration to control rd10 mice, they displayed a significant preservation of cone cells. Ultrastructural analysis of rd10 mouse retinas revealed that a substantial fraction of dying cones exhibited necrotic morphology, which was rescued by Rip3 deficiency. Additionally, pharmacologic treatment with a RIP kinase inhibitor attenuated histological and functional deficits of cones in rd10 mice. Thus, necrotic mechanisms involving RIP kinase are crucial in cone cell death in inherited retinal degeneration, suggesting the RIP kinase pathway as a potential target to protect cone-mediated central and peripheral vision loss in patients with retinitis pigementosa
Ashtekar's New Variables and Positive Energy
We discuss earlier unsuccessful attempts to formulate a positive
gravitational energy proof in terms of the New Variables of Ashtekar. We also
point out the difficulties of a Witten spinor type proof. We then use the
special orthonormal frame gauge conditions to obtain a locally positive
expression for the New Variables Hamiltonian and thereby a ``localization'' of
gravitational energy as well as a positive energy proof.Comment: 12 pages Plain Te
Another positivity proof and gravitational energy localizations
Two locally positive expressions for the gravitational Hamiltonian, one using
4-spinors the other special orthonormal frames, are reviewed. A new quadratic
3-spinor-curvature identity is used to obtain another positive expression for
the Hamiltonian and thereby a localization of gravitational energy and positive
energy proof. These new results provide a link between the other two methods.
Localization and prospects for quasi-localization are discussed.Comment: 14 pages REVTe
The Hamiltonian boundary term and quasi-local energy flux
The Hamiltonian for a gravitating region includes a boundary term which
determines not only the quasi-local values but also, via the boundary variation
principle, the boundary conditions. Using our covariant Hamiltonian formalism,
we found four particular quasi-local energy-momentum boundary term expressions;
each corresponds to a physically distinct and geometrically clear boundary
condition. Here, from a consideration of the asymptotics, we show how a
fundamental Hamiltonian identity naturally leads to the associated quasi-local
energy flux expressions. For electromagnetism one of the four is distinguished:
the only one which is gauge invariant; it gives the familiar energy density and
Poynting flux. For Einstein's general relativity two different boundary
condition choices correspond to quasi-local expressions which asymptotically
give the ADM energy, the Trautman-Bondi energy and, moreover, an associated
energy flux (both outgoing and incoming). Again there is a distinguished
expression: the one which is covariant.Comment: 12 pages, no figures, revtex
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