812 research outputs found
Snow water equivalent modeling components in NewAge-JGrass
This paper presents a package of modified temperature-index-based snow
water equivalent models as part of the hydrological modeling system
NewAge-JGrass. Three temperature-based snow models are integrated into the
NewAge-JGrass modeling system and use many of its components such as those
for radiation balance (short wave radiation balance, SWRB), kriging (KRIGING), automatic calibration
algorithms (particle swarm optimization) and tests of goodness of fit
(NewAge-V), to build suitable modeling solutions (MS). Similarly to all the
NewAge-JGrass components, the models can be executed both in raster and in
vector mode. The simulation time step can be daily, hourly or sub-hourly,
depending on user needs and availability of input data. The MS are applied on
the Cache la Poudre River basin (CO, USA) using three test applications.
First, daily snow water equivalent is simulated for three different
measurement stations for two snow model formulations. Second, hourly snow
water equivalent is simulated using all the three different snow model
formulae. Finally, a raster mode application is performed to compute snow
water equivalent maps for the whole Cache la Poudre Basin
Shadow features and shadow bands in the paramagnetic state of cuprate superconductors
The conditions for the precursors of antiferromagnetic bands in cuprate
superconductors are studied using weak-to-intermediate coupling approach. It is
shown that there are, in fact, three different precursor effects due to the
proximity to antiferromagnetic instability: i) the shadow band which associated
with new pole in the Green's function ii) the dispersive shadow feature due to
the thermal enhancement of the scattering rate and iii) the non-dispersive
shadow feature due to quantum spin fluctuation that exist only in
scan of the spectral function . I found
that dispersive shadow peaks in can exist at finite
temperature T in the renormalized classical regime, when ,
( is the characteristic energy of
spin fluctuations, is the thermal wave length of electron). In
contrast at zero temperature, only non-dispersive shadow feature in has been found. I found, however, that the latter
effect is always very small. The theory predict no shadow effects in the
optimally doped materials. The conditions for which shadow peaks can be
observed in photoemission are discussed.Comment: 6 pages, REVTEX, 2 ps figures, version to be published in PR
On different lagrangian formalisms for vector resonances within chiral perturbation theory
We study the relation of vector Proca field formalism and antisymmetric
tensor field formalism for spin-one resonances in the context of the large N_C
inspired chiral resonance Lagrangian systematically up to the order O(p6) and
give a transparent prescription for the transition from vector to antisymmetric
tensor Lagrangian and vice versa. We also discuss the possibility to describe
the spin-one resonances using an alternative "mixed" first order formalism,
which includes both types of fields simultaneously, and compare this one with
the former two. We also briefly comment on the compatibility of the above
lagrangian formalisms with the high-energy constraints for concrete VVP
correlator.Comment: 34 pages, 3 figure
Remnant Fermi Surfaces in Photoemission
Recent experiments have introduced a new concept for analyzing the
photoemission spectra of correlated electrons -- the remnant Fermi surface
(rFs), which can be measured even in systems which lack a conventional Fermi
surface. Here, we analyze the rFs in a number of interacting electron models,
and find that the results fall into two classes. For systems with pairing
instabilities, the rFs is an accurate replica of the true Fermi surface. In the
presence of nesting instabilities, the rFs is a map of the resulting
superlattice Brillouin zone. The results suggest that the gap in Ca_2CuO_2Cl_2
is of nesting origin.Comment: 4 pages LaTex, 3 ps figure
Theory for the excitation spectrum of High-T$_c superconductors : quasiparticle dispersion and shadows of the Fermi surface
Using a new method for the solution of the FLEX-equations, which allows the
determination of the self energy of the Hubbard
model on the real frequency axis, we calculate the doping dependence of the
quasi-particle excitations of High-T superconductors. We obtain new results
for the shadows of the Fermi surface, their dependence on the deformation of
the quasi particle dispersion, an anomalous -dependence of and a related violation of the Luttinger theorem.
This sheds new light on the influence of short range magnetic order on the low
energy excitations and its significance for photoemission experiments.Comment: 4 pages (REVTeX) with 3 figure
A momentum-dependent perspective on quasiparticle interference in Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta}
Angle Resolved Photoemission Spectroscopy (ARPES) probes the momentum-space
electronic structure of materials, and provides invaluable information about
the high-temperature superconducting cuprates. Likewise, the cuprate
real-space, inhomogeneous electronic structure is elucidated by Scanning
Tunneling Spectroscopy (STS). Recently, STS has exploited quasiparticle
interference (QPI) - wave-like electrons scattering off impurities to produce
periodic interference patterns - to infer properties of the QP in
momentum-space. Surprisingly, some interference peaks in
Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} (Bi-2212) are absent beyond the
antiferromagnetic (AF) zone boundary, implying the dominance of particular
scattering process. Here, we show that ARPES sees no evidence of quasiparticle
(QP) extinction: QP-like peaks are measured everywhere on the Fermi surface,
evolving smoothly across the AF zone boundary. This apparent contradiction
stems from different natures of single-particle (ARPES) and two-particle (STS)
processes underlying these probes. Using a simple model, we demonstrate
extinction of QPI without implying the loss of QP beyond the AF zone boundary
Magnetoresistance in Heavily Underdoped YBa_2Cu_3O_{6+x}: Antiferromagnetic Correlations and Normal-State Transport
We report on a contrasting behavior of the in-plane and out-of-plane
magnetoresistance (MR) in heavily underdoped antiferromagnetic (AF)
YBa_2Cu_3O_{6+x} (x<0.37). The out-of-plane MR (I//c) is positive over most of
the temperature range and shows a sharp increase, by about two orders of
magnitude, upon cooling through the Neel temperature T_N. A contribution
associated with the AF correlations is found to dominate the out-of-plane MR
behavior for H//c from far above T_N, pointing to the key role of spin
fluctuations in the out-of-plane transport. In contrast, the transverse
in-plane MR (I//a(b);H//c) appears to be small and smooth through T_N, implying
that the development of the AF order has little effect on the in-plane
resistivity.Comment: 4 pages, 5 figures, accepted for publication in Phys.Rev.Let
Fluctuation Conductivity in Insulator-Superconductor Transitions with Dissipation
We analyze here the fluctuation conductivity in the vicinity of the critical
point in a 2D Josephson junction array shunted by an Ohmic resistor.We find
that at the Gaussian level, the conductivity acquires a logarithmic dependence
on when the dissipation is sufficiently small. In the renormalized
classical regime, this logarithmic dependence gives rise to a leveling-off of
the resistivity at low to intermediate temperatures when fluctuations are
included. We show, however, that this trend does not persist to T=0 at which
point the resistivity vanishes. The possible relationship of the leveling of
the resistivity to the low temperature transport in granlar superconductors is
discussed.Comment: 4 page
Pairing Correlations in the Two-Dimensional Hubbard Model
We present the results of a quantum Monte Carlo study of the extended and
the pairing correlation functions for the two-dimensional Hubbard
model, computed with the constrained-path method. For small lattice sizes and
weak interactions, we find that the pairing correlations are
stronger than the extended pairing correlations and are positive when the
pair separation exceeds several lattice constants. As the system size or the
interaction strength increases, the magnitude of the long-range part of both
correlation functions vanishes.Comment: 4 pages, RevTex, 4 figures included; submitted to Phys. Rev. Let
QED radiative corrections to the decay pi^0 to e^+e^-
We reconsider QED radiative corrections (RC) to the
decay width. One kind of RC investigated earlier has a renormalization group
origin and can be associated with the final state interaction of electron and
positron. It determines the distribution of lepton pair invariant masses in the
whole kinematic region. The other type of RC has a double-logarithmic character
and is related to almost on-mass-shell behavior of the lepton form factors. The
total effect of RC for the decay is estimated to be
3.2% and for the decay is 4.3%.Comment: 12 pages, 3 figure
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