16,643 research outputs found
On the road to prosperity? The economic geography of China's national expressway network
Over the past two decades, China has embarked on an ambitious program of expressway network expansion. By facilitating market integration, this program aims both to promote efficiency at the national level and to contribute to the catch-up of lagging inland regions with prosperous Eastern ones. This paper evaluates the aggregate and spatial economic impacts of China's newly constructed National Expressway Network, focussing, in particular, on its short-run impacts. To achieve this aim, the authors adopt a counterfactual approach based on the estimation and simulation of a structural "new economic geography" model. Overall, they find that aggregate Chinese real income was approximately 6 percent higher than it would have been in 2007 had the expressway network not been built. Although there is considerable heterogeneity in the results, the authors do not find evidence of a significant reduction in disparities across prefectural level regions or of a reduction in urban-rural disparities. If anything, the expressway network appears to have reinforced existing patterns of spatial inequality, although, over time, these will likely be reduced by enhanced migration
Theoretical Predictions of Superconductivity in Alkali Metals under High Pressure
We calculated the superconductivity properties of alkali metals under high
pressure using the results of band theory and the rigid-muffin-tin theory of
Gaspari and Gyorffy. Our results suggest that at high pressures Lithium,
Potassium, Rubidium and Cesium would be superconductors with transition
temperatures approaching . Our calculations also suggest that Sodium
would not be a superconductor under high pressure even if compressed to less
than half of its equilibrium volume. We found that the compression of the
lattice strengthens the electron-phonon coupling through a delicately balanced
increase of both the electronic and phononic components of this coupling. This
increase of the electron-phonon coupling in Li is due to an enhancement of the
- channel of the interaction, while in the heavier elements the -
channel is the dominant component.Comment: 6 pages, 8 figure
Polarizabilities of the 87Sr Clock Transition
In this paper, we propose an in-depth review of the vector and tensor
polarizabilities of the two energy levels of the 87Sr clock transition whose
measurement was reported in [P. G. Westergaard et al., Phys. Rev. Lett. 106,
210801 (2011)]. We conduct a theoretical calculation that reproduces the
measured coefficients. In addition, we detail the experimental conditions used
for their measurement in two Sr optical lattice clocks, and exhibit the
quadratic behaviour of the vector and tensor shifts with the depth of the
trapping potential and evaluate their impact on the accuracy of the clock
Non-Markovian Fermionic Stochastic Schr\"{o}dinger Equation for Open System Dynamics
In this paper we present an exact Grassmann stochastic Schr\"{o}dinger
equation for the dynamics of an open fermionic quantum system coupled to a
reservoir consisting of a finite or infinite number of fermions. We use this
stochastic approach to derive the exact master equation for a fermionic system
strongly coupled to electronic reservoirs. The generality and applicability of
this Grassmann stochastic approach is justified and exemplified by several
quantum open system problems concerning quantum decoherence and quantum
transport for both vacuum and finite-temperature fermionic reservoirs. We show
that the quantum coherence property of the quantum dot system can be profoundly
modified by the environment memory.Comment: 10.5 pages, 3 figure
Machine Learning based Trust Computational Model for IoT Services
The Internet of Things has facilitated access to a large volume of sensitive information on each participating object in an ecosystem. This imposes many threats ranging from the risks of data management to the potential discrimination enabled by data analytics over delicate information such as locations, interests, and activities. To address these issues, the concept of trust is introduced as an important role in supporting both humans and services to overcome the perception of uncertainty and risks before making any decisions. However, establishing trust in a cyber world is a challenging task due to the volume of diversified influential factors from cyber-physical-systems. Hence, it is essential to have an intelligent trust computation model that is capable of generating accurate and intuitive trust values for prospective actors. Therefore, in this paper, a quantifiable trust assessment model is proposed. Built on this model, individual trust attributes are then calculated numerically. Moreover, a novel algorithm based on machine learning principles is devised to classify the extracted trust features and combine them to produce a final trust value to be used for decision making. Finally, our model’s effectiveness is verified through a simulation. The results show that our method has advantages over other aggregation methods
Extremely high magnetoresistance and conductivity in the type-II Weyl semimetals WP2 and MoP2
The peculiar band structure of semimetals exhibiting Dirac and Weyl crossings
can lead to spectacular electronic properties such as large mobilities
accompanied by extremely high magnetoresistance. In particular, two closely
neighbouring Weyl points of the same chirality are protected from annihilation
by structural distortions or defects, thereby significantly reducing the
scattering probability between them. Here we present the electronic properties
of the transition metal diphosphides, WP2 and MoP2, that are type-II Weyl
semimetals with robust Weyl points. We present transport and angle resolved
photoemission spectroscopy measurements, and first principles calculations. Our
single crystals of WP2 display an extremely low residual low-temperature
resistivity of 3 nohm-cm accompanied by an enormous and highly anisotropic
magnetoresistance above 200 million % at 63 T and 2.5 K. These properties are
likely a consequence of the novel Weyl fermions expressed in this compound. We
observe a large suppression of charge carrier backscattering in WP2 from
transport measurements.Comment: Appeared in Nature Communication
Superconducting and normal-state interlayer-exchange-coupling in LaSrMnO-YBaCuO_{0.67}_{0.33}{3}$ epitaxial trilayers
The issue of interlayer exchange coupling in magnetic multilayers with
superconducting (SC) spacer is addressed in LaSrMnO
(LSMO) - YBaCuO (YBCO) - LaSrMnO
(LSMO) epitaxial trilayers through resistivity, ac-susceptibility and
magnetization measurements. The ferromagnetic (FM) LSMO layers possessing
in-plane magnetization suppress the critical temperature (T of the
c-axis oriented YBCO thin film spacer. The superconducting order, however,
survives even in very thin layers (thickness d 50 {\AA}, 4
unit cells) at T 25 K. A predominantly antiferromagnetic (AF) exchange
coupling between the moments of the LSMO layers at fields 200 Oe is seen in
the normal as well as the superconducting states of the YBCO spacer. The
exchange energy J ( 0.08 erg/cm at 150 K for d = 75
{\AA}) grows on cooling down to T, followed by truncation of this growth
on entering the superconducting state. The coupling energy J at a fixed
temperature drops exponentially with the thickness of the YBCO layer. The
temperature and d dependencies of this primarily non-oscillatory J
are consistent with the coupling theories for systems in which transport is
controlled by tunneling. The truncation of the monotonic T dependence of
J below T suggests inhibition of single electron tunneling across
the CuO planes as the in-plane gap parameter acquires a non-zero value.Comment: Accepted for publication in Phys. Rev.
Effects of thermal fluctuation and the receptor-receptor interaction in bacterial chemotactic signalling and adaptation
Bacterial chemotaxis is controlled by the conformational changes of the
receptors, in response to the change of the ambient chemical concentration. In
a statistical mechanical approach, the signalling due to the conformational
changes is a thermodynamic average quantity, dependent on the temperature and
the total energy of the system, including both ligand-receptor interaction and
receptor-receptor interaction. This physical theory suggests to biology a new
understanding of cooperation in ligand binding and receptor signalling
problems. How much experimental support of this approach can be obtained from
the currently available data? What are the parameter values? What is the
practical information for experiments? Here we make comparisons between the
theory and recent experimental results. Although currently comparisons can only
be semi-quantitative or qualitative, consistency is clearly shown. The theory
also helps to sort a variety of data.Comment: 26 pages, revtex. Journal version. Analysis on another set of data on
adaptation time is adde
Mesoscopic Electron and Phonon Transport through a Curved Wire
There is great interest in the development of novel nanomachines that use
charge, spin, or energy transport, to enable new sensors with unprecedented
measurement capabilities. Electrical and thermal transport in these mesoscopic
systems typically involves wave propagation through a nanoscale geometry such
as a quantum wire. In this paper we present a general theoretical technique to
describe wave propagation through a curved wire of uniform cross-section and
lying in a plane, but of otherwise arbitrary shape. The method consists of (i)
introducing a local orthogonal coordinate system, the arclength and two locally
perpendicular coordinate axes, dictated by the shape of the wire; (ii)
rewriting the wave equation of interest in this system; (iii) identifying an
effective scattering potential caused by the local curvature; and (iv), solving
the associated Lippmann-Schwinger equation for the scattering matrix. We carry
out this procedure in detail for the scalar Helmholtz equation with both
hard-wall and stress-free boundary conditions, appropriate for the mesoscopic
transport of electrons and (scalar) phonons. A novel aspect of the phonon case
is that the reflection probability always vanishes in the long-wavelength
limit, allowing a simple perturbative (Born approximation) treatment at low
energies. Our results show that, in contrast to charge transport, curvature
only barely suppresses thermal transport, even for sharply bent wires, at least
within the two-dimensional scalar phonon model considered. Applications to
experiments are also discussed.Comment: 9 pages, 11 figures, RevTe
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