102,486 research outputs found
Theory of the quasiparticle excitation in high T cuprates: quasiparticle charge and nodal-antinodal dichotomy
A variational theory is proposed for the quasiparticle excitation in high
T cuprates. The theory goes beyond the usual Gutzwiller projected mean
field state description by including the spin-charge recombination effect in
the RVB background. The spin-charge recombination effect is found to
qualitatively alter the behavior of the quasiparticle charge as a function of
doping and cause considerable anisotropy in quasiparticle weight on the Fermi
surface.Comment: 10 page
ASAP : towards accurate, stable and accelerative penetrating-rank estimation on large graphs
Pervasive web applications increasingly require a measure of similarity among objects. Penetrating-Rank (P-Rank) has been one of the promising link-based similarity metrics as it provides a comprehensive way of jointly encoding both incoming and outgoing links into computation for emerging applications. In this paper, we investigate P-Rank efficiency problem that encompasses its accuracy, stability and computational time. (1) We provide an accuracy estimate for iteratively computing P-Rank. A symmetric problem is to find the iteration number K needed for achieving a given accuracy ε. (2) We also analyze the stability of P-Rank, by showing that small choices of the damping factors would make P-Rank more stable and well-conditioned. (3) For undirected graphs, we also explicitly characterize the P-Rank solution in terms of matrices. This results in a novel non-iterative algorithm, termed ASAP , for efficiently computing P-Rank, which improves the CPU time from O(n 4) to O( n 3 ). Using real and synthetic data, we empirically verify the effectiveness and efficiency of our approaches
The role of electron and phonon temperatures in the helicity-independent all-optical switching of GdFeCo
Ultrafast optical heating of the electrons in ferrimagnetic metals can result
in all-optical switching (AOS) of the magnetization. Here we report
quantitative measurements of the temperature rise of GdFeCo thin films during
helicity-independent AOS. Critical switching fluences are obtained as a
function of the initial temperature of the sample and for laser pulse durations
from 55 fs to 15 ps. We conclude that non-equilibrium phenomena are necessary
for helicity-independent AOS, although the peak electron temperature does not
play a critical role. Pump-probe time-resolved experiments show that the
switching time increases as the pulse duration increases, with 10 ps pulses
resulting in switching times of ~sim 13 ps. These results raise new questions
about the fundamental mechanism of helicity-independent AOS.Comment: 18 pages, 6 figures and supplementary material
The Mid-Infrared Extinction Law and its Variation in the Coalsack Nebula
In recent years the wavelength dependence of interstellar extinction from the
ultraviolet (UV), optical, through the near- and mid-infrared (IR) has been
studied extensively. Although it is well established that the UV/optical
extinction law varies significantly among the different lines of sight, it is
not clear how the IR extinction varies among various environments. In this
work, using the color-excess method and taking red giants as the extinction
tracer, we determine the interstellar extinction Alambda in the four
Spitzer/IRAC bands of the Coalsack nebula, a nearby starless dark cloud, based
on the data obtained from the 2MASS and Spitzer/GLIMPSE surveys. We select five
individual regions across the nebula that span a wide variety of physical
conditions, ranging from diffuse, translucent to dense environments, as traced
by the visual extinction, the Spitzer/MIPS 24micron emission, and CO emission.
We find that Alambda/AKs, the mid-IR extinction relative to AKs, decreases from
diffuse to dense environments, which may be explained in terms of ineffective
dust growth in dense regions. The mean extinction (relative to AKs) is
calculated for the four IRAC bands as well, which exhibits a flat mid-IR
extinction law, consistent with previous determinations for other regions. The
extinction in the IRAC 4.5micron band is anomalously high, much higher than
that of the other three IRAC bands. It cannot be explained in terms of CO and
CO2 ices. The mid-IR extinction in the four IRAC bands have also been derived
for four representative regions in the Coalsack Globule 2 which respectively
exhibit strong ice absorption, moderate or weak ice absorption, and very weak
or no ice absorption. The derived mid-IR extinction curves are all flat, with
Alambda/AKs increasing with the decrease of the H2O ice absorption optical
depth.Comment: 39 pages, 13 figures, accepted by Ap
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Reaction Mechanisms for Long-Life Rechargeable Zn/MnO 2 Batteries
Rechargeable aqueous Zn-ion batteries (ZIBs) are very promising for large-scale grid energy storage applications owing to their low cost, environmentally benign constituents, excellent safety, and relatively high energy density. Their usage, however, is largely hampered by the fast capacity fade. The complexity of the reactions has resulted in long-standing ambiguities of the chemical pathways of Zn/MnO 2 system. In this study, we find that both H + /Zn 2+ intercalation and conversion reactions occur at different voltages and that the rapid capacity fading can clearly be ascribed to the rate-limiting and irreversible conversion reactions at a lower voltage. By limiting the irreversible conversion reactions at â1.26 V, we successfully demonstrate ultrahigh power and long life that are superior to most of the reported ZIBs or even some lithium-ion batteries
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