233 research outputs found
Anomalous temperature dependence of the single-particle spectrum in the organic conductor TTF-TCNQ
The angle-resolved photoemission spectrum of the organic conductor TTF-TCNQ
exhibits an unusual transfer of spectral weight over a wide energy range for
temperatures 60K<T<260K. In order to investigate the origin of this finding,
here we report numerical results on the single-particle spectral weight
A(k,omega) for the one-dimensional (1D) Hubbard model and, in addition, for the
1D extended Hubbard and the 1D Hubbard-Holstein models. Comparisons with the
photoemission data suggest that the 1D Hubbard model is not sufficient for
explaining the unusual T dependence, and the long-range part of the Coulomb
repulsion also needs to be included.Comment: 4 pages, 4 figure
Temperature dependence of spinon and holon excitations in one-dimensional Mott insulators
Motivated by the recent angle-resolved photoemission spectroscopy (ARPES)
measurements on one-dimensional Mott insulators, SrCuO and
NaVO, we examine the single-particle spectral weight
of the one-dimensional (1D) Hubbard model at half-filling. We are particularly
interested in the temperature dependence of the spinon and holon excitations.
For this reason, we have performed the dynamical density matrix renormalization
group and determinantal quantum Monte Carlo (QMC) calculations for the
single-particle spectral weight of the 1D Hubbard model. In the QMC data, the
spinon and holon branches become observable at temperatures where the
short-range antiferromagnetic correlations develop. At these temperatures, the
spinon branch grows rapidly. In the light of the numerical results, we discuss
the spinon and holon branches observed by the ARPES experiments on
SrCuO. These numerical results are also in agreement with the
temperature dependence of the ARPES results on NaVO.Comment: 8 pages, 8 figure
Economic instruments and resource use in a recyclable product market
By constructing a static model of a recyclable product market where the product can be manufactured by using both a recycled material and a harvested natural resource, we examine how different types of economic policy instruments affect resource harvesting activities of individual producers. In particular, we show that an increase in a recycling subsidy for consumers and an increase in a waste disposal fee on consumers can respectively lead to an increase in the resource harvest level. We explore the conditions under which these economic instruments are likely to backfire in terms of natural resource conservation
Signal and noise in regime systems: a hypothesis on the predictability of the North Atlantic Oscillation
Studies conducted by the UK Met Office reported significant skill at
predicting the winter NAO index with their seasonal prediction system. At the
same time, a very low signal-to-noise ratio was observed, as measured using the
`ratio of predictable components' (RPC) metric. We analyse both the skill and
signal-to-noise ratio using a new statistical toy-model which assumes NAO
predictability is driven by regime dynamics. It is shown that if the system is
approximately bimodal in nature, with the model consistently underestimating
the level of regime persistence each season, then both the high skill and high
RPC value of the Met Office hindcasts can easily be reproduced. Underestimation
of regime persistence could be attributable to any number of sources of model
error, including imperfect regime structure or errors in the propagation of
teleconnections. In particular, a high RPC value for a seasonal mean prediction
may be expected even if the models internal level of noise is realistic.Comment: Published in the Quarterly Journal of the Royal Meteorological
Society (2019
Photoinduced charge and spin dynamics in strongly correlated electron systems
Motivated by photoinduced phase transition in manganese oxides, charge and
spin dynamics induced by photoirradiation are examined. We calculate the
transient optical absorption spectra of the extended double-exchange model by
the density matrix renormalization group (DMRG) method. A charge-ordered
insulating (COI) state becomes metallic just after photoirradiation, and the
system tends to recover the initial COI state. The recovery is accompanied with
remarkable suppression of an antiferromagnetic correlation in the COI state.
The DMRG results are consistent with recent pump-probe spectroscopy data.Comment: 5 pages, 4 figure
Generation of maximum spin entanglement induced by cavity field in quantum-dot systems
Equivalent-neighbor interactions of the conduction-band electron spins of
quantum dots in the model of Imamoglu et al. [Phys. Rev. Lett. 83, 4204 (1999)]
are analyzed. Analytical solution and its Schmidt decomposition are found and
applied to evaluate how much the initially excited dots can be entangled to the
remaining dots if all of them are initially disentangled. It is demonstrated
that the perfect maximally entangled states (MES) can only be generated in the
systems of up to 6 dots with a single dot initially excited. It is also shown
that highly entangled states, approximating the MES with a good accuracy, can
still be generated in systems of odd number of dots with almost half of them
being excited. A sudden decrease of entanglement is observed by increasing the
total number of dots in a system with a fixed number of excitations.Comment: 6 pages, 7 figures, to appear in Phys. Rev.
A Cell of One’s Own? Incarceration and Other Turning Points in Women’s Journeys to Desistance
Research has shown the importance of turning points in desistance from criminal behavior. Using qualitative data from a sample of 100 formerly incarcerated mothers interviewed about their criminal behavior, this article explores their descriptions of transition moments and whether and how those moments affected their criminal behavior. The findings indicate that whereas parenting emerges as a turning point, the practical difficulties of reentry may reduce the impact of mothering on women’s desistance. More self-focused turning points, such as those due to incarceration, arrest, and sobriety appeared to be particularly important to the women’s desistance. This article emphasizes the need for research into the subjective and environmental factors that affect women’s desistance behaviors
A 4D-Var inversion system based on the icosahedral grid model (NICAM-TM 4D-Var v1.0) – Part 2: Optimization scheme and identical twin experiment of atmospheric CO<sub>2</sub> inversion
A four-dimensional variational method (4D-Var) is a popular technique for
source/sink inversions of atmospheric constituents, but it is not without
problems. Using an icosahedral grid transport model and the 4D-Var method, a
new atmospheric greenhouse gas (GHG) inversion system has been developed. The
system combines offline forward and adjoint models with a quasi-Newton
optimization scheme. The new approach is then used to conduct identical twin
experiments to investigate optimal system settings for an atmospheric
CO2 inversion problem, and to demonstrate the validity of the new
inversion system. In this paper, the inversion problem is simplified by
assuming the prior flux errors to be reasonably well known and by designing
the prior error correlations with a simple function as a first step. It is
found that a system of forward and adjoint models with smaller model errors
but with nonlinearity has comparable optimization performance to that of
another system that conserves linearity with an exact adjoint relationship.
Furthermore, the effectiveness of the prior error correlations is
demonstrated, as the global error is reduced by about 15 % by adding
prior error correlations that are simply designed when 65 weekly flask
sampling observations at ground-based stations are used. With the optimal
setting, the new inversion system successfully reproduces the spatiotemporal
variations of the surface fluxes, from regional (such as biomass burning) to
global scales. The optimization algorithm introduced in the new system does
not require decomposition of a matrix that establishes the correlation among
the prior flux errors. This enables us to design the prior error covariance
matrix more freely
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