9,124 research outputs found
Itinerant and localized magnetism on the triangular lattice: sodium rich phases of NaCoO
We study the interplay between correlation, itinerant ferromagnetism and
local moment formation on the electron doped triangular lattice of sodium
cobaltates NaCoO. We find that strong correlation renormalizes the
Stoner criterion and stabilizes the paramagnetic state for .
For , ferromagnetic (FM) order emerges. The enhanced Na dopant potential
fluctuations play a crucial role in the sodium rich phases and lead to an
inhomogeneous FM state, exhibiting nonmagnetic Co patches,
antiferromagnetic (AF) correlated regions, and FM clusters with AF domains.
Hole doping the band insulator at x=1 leads to the formation of local moments
near the Na vacancies and AF correlated magnetic clusters. We explain recent
observations by neutron, SR, and NMR experiments on the evolution of the
magnetic properties in the sodium rich phases.Comment: revtex4 file, 5 pages, 3 figures, published versio
On the coexistence and complementarity of Chinese translation methods of English metrical poetry
The Chinese translation of English metrical poetry has a history of more than one
hundred years, but it is still controversial on how to translate English metrical poetry into
Chinese. Chinese translators have hitherto devised three methods to render English
metrical poetry: sinolization, liberalization, and poetic form transplantation. Translators
practicing the methods of sinolization and liberalization belong to the group in favor of
spiritual resemblance. Translators who follow the method of poetic form transplantation
belong to the group in favor of formal resemblance. It is quite obvious that the two
groups have disagreement on the translation standard or guiding principle. Actually the
translation standards of the two groups can coexist, and the translation methods under the
guidance of these different translation standards can coexist and complement each other.
It is impractical and impossible to use one Chinese translation method or standard to
guide all the Chinese translation practice, and the diverse Chinese translation methods of
English metrical poetry can coexist and complement each other in the foreseeable future
Charging Autonomous Electric Vehicle Fleet for Mobility-on-Demand Services: Plug in or Swap out?
This paper compares two prevalent charging strategies for electric vehicles,
plug-in charging and battery swapping, to investigate which charging strategy
is superior for electric autonomous mobility-on-demand (AMoD) systems. To this
end, we use a queueing-theoretic model to characterize the vehicle waiting time
at charging stations and battery swapping stations, respectively. The model is
integrated into an economic analysis of the electric AMoD system operated by a
transportation network company (TNC), where the incentives of passengers, the
charging/operating shift of TNC vehicles, the operational decisions of the
platform, and the planning decisions of the government are captured. Overall, a
bi-level optimization framework is proposed for charging infrastructure
planning of the electric AMoD system. Based on the proposed framework, we
compare the socio-economic performance of plug-in charging and battery
swapping, and investigate how this comparison depends on the evolving charging
technologies (such as charging speed, battery capacity, and infrastructure
cost). At the planning level, we find that when choosing plug-in charging,
increased charging speed leads to a transformation of infrastructure from
sparsely distributed large stations to densely distributed small stations,
while enlarged battery capacity transforms the infrastructure from densely
distributed small stations to sparsely distributed large stations. On the other
hand, when choosing battery swapping, both increased charging speed and
enlarged battery capacity will lead to a smaller number of battery swapping
stations. At the operational level, we find that improved charging speed leads
to increased TNC profit when choosing plug-in charging, whereas improved
charging speed may lead to smaller TNC profit under battery swapping. The above
insights are validated through realistic numerical studies
CUBOS: An Internal Cluster Validity Index for Categorical Data
Internal cluster validity index is a powerful tool for evaluating clustering performance. The study on internal cluster validity indices for categorical data has been a challenging task due to the difficulty in measuring distance between categorical attribute values. While some efforts have been made, they ignore the relationship between different categorical attribute values and the detailed distribution information between data objects. To solve these problems, we propose a novel index called Categorical data cluster Utility Based On Silhouette (CUBOS). Specifically, we first make clear the superiority of the paradigm of Silhouette index in exploring the details of clustering results. Then, we raise the Improved Distance metric for Categorical data (IDC) inspired by Category Distance to measure distance between categorical data exactly. Finally, the paradigm of Silhouette index and IDC are combined to construct the CUBOS, which can overcome the aforementioned shortcomings and produce more accurate evaluation results than other baselines, as shown by the experimental results on several UCI datasets
Regulating For-Hire Autonomous Vehicles for An Equitable Multimodal Transportation Network
This paper assesses the equity impacts of for-hire autonomous vehicles (AVs)
and investigates regulatory policies that promote spatial and social equity in
future autonomous mobility ecosystems. To this end, we consider a multimodal
transportation network, where a ride-hailing platform operates a fleet of AVs
to offer mobility-on-demand services in competition with a public transit
agency that offers transit services on a transportation network. A
game-theoretic model is developed to characterize the intimate interactions
between the ride-hailing platform, the transit agency, and multiclass
passengers with distinct income levels. An algorithm is proposed to compute the
Nash equilibrium of the game and conduct an ex-post evaluation of the
performance of the obtained solution. Based on the proposed framework, we
evaluate the spatial and social equity in transport accessibility using the
Theil index, and find that although the proliferation of for-hire AVs in the
ride-hailing network improves overall accessibility, the benefits are not
fairly distributed among distinct locations or population groups, implying that
the deployment of AVs will enlarge the existing spatial and social inequity
gaps in the transportation network if no regulatory intervention is in place.
To address this concern, we investigate two regulatory policies that can
improve transport equity: (a) a minimum service-level requirement on
ride-hailing services, which improves the spatial equity in the transport
network; (b) a subsidy on transit services by taxing ride-hailing services,
which promotes the use of public transit and improves the spatial and social
equity of the transport network. We show that the minimum service-level
requirement entails a trade-off: as a higher minimum service level is imposed,
the spatial inequity reduces, but the social inequity will be exacerbated. On
the other hand ..
Electron correlation and Fermi surface topology of NaCoO
The electronic structure of NaCoO revealed by recent photoemission
experiments shows important deviations from band theory predictions. The six
small Fermi surface pockets predicted by LDA calculations have not been
observed as the associated band fails to cross the Fermi level for
a wide range of sodium doping concentration . In addition, significant
bandwidth renormalizations of the complex have been observed. We show
that these discrepancies are due to strong electronic correlations by studying
the multi-orbital Hubbard model in the Hartree-Fock and strong-coupling
Gutzwiller approximation. The quasiparticle dispersion and the Fermi surface
topology obtained in the presence of strong local Coulomb repulsion are in good
agreement with experiments.Comment: 5 pages, 4 figures, revtex4; minor changes, to be published in Phys.
Rev. Let
On Orientifold Constructions of Type IIA Dual Pairs
In this paper we analyze the earlier constructions of the type IIA dual pairs
through orientifolding. By an appropriate choice of -matrix basis for
the spinor representations of the -duality group, we give an explicit
relationship between the orientifold models and their dual pairs.Comment: 11pages, Late
- …