4,756 research outputs found
Orbital-transverse density-wave instabilities in iron-based superconductors
Besides the conventional spin-density-wave (SDW) state, a new kind of
orbital-transverse density-wave (OTDW) state is shown to exist generally in
multi-orbital systems. We demonstrate that the orbital character of Fermi
surface nesting plays an important role in density responses. The relationship
between antiferromagnetism and structural phase transition in LaFeAsO (1111)
and BaFeAs (122) compounds of iron-based superconductors may be
understood in terms of the interplay between the SDW and OTDW with a
five-orbital Hamiltonian. We propose that the essential difference between 1111
and 122 compounds is crucially determined by the presence of the
two-dimensional -like Fermi surface around (0,0) being only in 1111
parent compounds.Comment: several parts were rewritten for clarity. 6 pages, 3 figures, 1 tabl
Transonic Shocks In Multidimensional Divergent Nozzles
We establish existence, uniqueness and stability of transonic shocks for
steady compressible non-isentropic potential flow system in a multidimensional
divergent nozzle with an arbitrary smooth cross-section, for a prescribed exit
pressure. The proof is based on solving a free boundary problem for a system of
partial differential equations consisting of an elliptic equation and a
transport equation. In the process, we obtain unique solvability for a class of
transport equations with velocity fields of weak regularity(non-Lipschitz), an
infinite dimensional weak implicit mapping theorem which does not require
continuous Frechet differentiability, and regularity theory for a class of
elliptic partial differential equations with discontinuous oblique boundary
conditions.Comment: 54 page
Stability Of contact discontinuity for steady Euler System in infinite duct
In this paper, we prove structural stability of contact discontinuities for
full Euler system
Estimating daily evapotranspiration based on a model of evaporative fraction (EF) for mixed pixels
Currently, applications of remote sensing evapotranspiration (ET) products
are limited by the coarse resolution of satellite remote sensing data caused
by land surface heterogeneities and the temporal-scale extrapolation of the
instantaneous latent heat flux (LE) based on satellite overpass time. This
study proposes a simple but efficient model (EFAF) for estimating the daily
ET of remotely sensed mixed pixels using a model of the evaporative
fraction (EF) and area fraction (AF) to increase the accuracy of ET estimate
over heterogeneous land surfaces. To accomplish this goal, we derive an
equation for calculating the EF of mixed pixels based on two key hypotheses.
Hypothesis 1 states that the available energy (AE) of each sub-pixel is
approximately equal to that of any other sub-pixels in the same mixed pixel
within an acceptable margin of error and is equivalent to the AE of the mixed
pixel. This approach simplifies the equation, and uncertainties and errors
related to the estimated ET values are minor. Hypothesis 2 states that the EF
of each sub-pixel is equal to that of the nearest pure pixel(s) of the same
land cover type. This equation is designed to correct spatial-scale errors
for the EF of mixed pixels; it can be used to calculate daily ET from daily
AE data. The model was applied to an artificial oasis located in the
midstream area of the Heihe River using HJ-1B satellite data with a 300 m
resolution. The results generated before and after making corrections were
compared and validated using site data from eddy covariance systems. The
results show that the new model can significantly improve the accuracy of
daily ET estimates relative to the lumped method; the coefficient of
determination (R2) increased to 0.82 from 0.62, the root mean square
error (RMSE) decreased to 1.60 from 2.47 MJ mâ2(decreased
approximately to 0.64 from 0.99 mm) and the mean bias error (MBE) decreased
from 1.92Â to 1.18 MJ mâ2 (decreased from approximately 0.77Â to
0.47 mm). It is concluded that EFAF can reproduce daily ET with reasonable
accuracy; can be used to produce the ET product; and can be applied to
hydrology research, precision agricultural management and monitoring natural
ecosystems in the future.</p
Object Picture of Quasinormal Modes for Stringy Black Holes
We study the quasinormal modes (QNMs) for stringy black holes. By using
numerical calculation, the relations between the QNMs and the parameters of
black holes are minutely shown. For (1+1)-dimensional stringy black hole, the
real part of the quasinormal frequency increases and the imaginary part of the
quasinormal frequency decreases as the mass of the black hole increases.
Furthermore, the dependence of the QNMs on the charge of the black hole and the
flatness parameter is also illustrated. For (1+3)-dimensional stringy black
hole, increasing either the event horizon or the multipole index, the real part
of the quasinormal frequency decreases. The imaginary part of the quasinormal
frequency increases no matter whether the event horizon is increased or the
multipole index is decreased.Comment: 4 pages, 5 figure
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