4,665 research outputs found
Measures Of International Transport Cost For OECD Countries
This paper presents new estimates of country-specific international transport costs for 21 OECD countries over the period 1973-2005. The methodology is based on direct measures of air, maritime, and road transport costs rather than on cif/fob ratios or other balance of payments data employed in previous studies. Transport costs are calculated as costs per kilogramme for each mode of transport at a bilateral level and then aggregated. Australia and New Zealand are found to have the highest transport costs among the OECD countries considered, followed by Japan. The time trends are sensitive to the choice of deflator, but the results do not show an overall downward trend in transport costs for OECD countries, contrary to conventional wisdom, but consistent with Hummels’ (2007) recent study of global transport costs
Fan-spine topology formation through two-step reconnection driven by twisted flux emergence
We address the formation of 3D nullpoint topologies in the solar corona by
combining Hinode/XRT observations of a small dynamic limb event, which occurred
beside a non-erupting prominence cavity, with a 3D zero-beta MHD simulation. To
this end, we model the boundary-driven kinematic emergence of a compact,
intense, and uniformly twisted flux tube into a potential field arcade that
overlies a weakly twisted coronal flux rope. The expansion of the emerging flux
in the corona gives rise to the formation of a nullpoint at the interface of
the emerging and the pre-existing fields. We unveil a two-step reconnection
process at the nullpoint that eventually yields the formation of a broad 3D
fan-spine configuration above the emerging bipole. The first reconnection
involves emerging fields and a set of large-scale arcade field lines. It
results in the launch of a torsional MHD wave that propagates along the
arcades, and in the formation of a sheared loop system on one side of the
emerging flux. The second reconnection occurs between these newly formed loops
and remote arcade fields, and yields the formation of a second loop system on
the opposite side of the emerging flux. The two loop systems collectively
display an anenome pattern that is located below the fan surface. The flux that
surrounds the inner spine field line of the nullpoint retains a fraction of the
emerged twist, while the remaining twist is evacuated along the reconnected
arcades. The nature and timing of the features which occur in the simulation do
qualititatively reproduce those observed by XRT in the particular event studied
in this paper. Moreover, the two-step reconnection process suggests a new
consistent and generic model for the formation of anemone regions in the solar
corona.Comment: Accepted for publication in ApJ, 11 pages and 5 figure
A network approach to public goods
Suppose agents can exert costly effort that creates nonrival, heterogeneous benefits for each other. At each possible outcome, a weighted, directed network describing marginal externalities is defined. We show that Pareto efficient outcomes are those at which the largest eigenvalue of the network is 1. An important set of efficient solutions - Lindahl outcomes - are characterized by contributions being proportional to agents' eigenvector centralities in the network. The outcomes we focus on are motivated by negotiations. We apply the results to identify who is essential for Pareto improvements, how to efficiently subdivide negotiations, and whom to optimally add to a team
Impact of motion along the field direction on geometric-phase-induced false electric dipole moment signals
Geometric-phase-induced false electric dipole moment (EDM) signals, resulting
from interference between magnetic field gradients and particle motion in
electric fields, have been studied extensively in the literature, especially
for neutron EDM experiments utilizing stored ultracold neutrons and
co-magnetometer atoms. Previous studies have considered particle motion in the
transverse plane perpendicular to the direction of the applied electric and
magnetic fields. We show, via Monte Carlo studies, that motion along the field
direction can impact the magnitude of this false EDM signal if the wall
surfaces are rough such that the wall collisions can be modeled as diffuse,
with the results dependent on the size of the storage cell's dimension along
the field direction.Comment: 7 pages, 3 figures, NIM A, in pres
Algorithms and literate programs for weighted low-rank approximation with missing data
Linear models identification from data with missing values is posed as a weighted low-rank approximation problem with weights related to the missing values equal to zero. Alternating projections and variable projections methods for solving the resulting problem are outlined and implemented in a literate programming style, using Matlab/Octave's scripting language. The methods are evaluated on synthetic data and real data from the MovieLens data sets
Effect of nonlocal interactions on the disorder-induced zero-bias anomaly in the Anderson-Hubbard model
To expand the framework available for interpreting experiments on disordered
strongly correlated systems, and in particular to explore further the
strong-coupling zero-bias anomaly found in the Anderson-Hubbard model, we ask
how this anomaly responds to the addition of nonlocal electron-electron
interactions. We use exact diagonalization to calculate the single-particle
density of states of the extended Anderson-Hubbard model. We find that for weak
nonlocal interactions the form of the zero-bias anomaly is qualitatively
unchanged. The energy scale of the anomaly continues to be set by an effective
hopping amplitude renormalized by the nonlocal interaction. At larger values of
the nonlocal interaction strength, however, hopping ceases to be a relevant
energy scale and higher energy features associated with charge correlations
dominate the density of states.Comment: 9 pages, 7 figure
New cantacaderid lace bugs from Dominician amber (Heteroptera: Tingidae, Catacaderiane)
New fossil tingids, representatives of the small subfamily Cantacaderinae (Tingidae) from the Oligocene Dominican amber, are described and discussed. The fossil species Eocader babyrussus n. sp. belongs to the recent neotropical genus Eocader of the tribe Phatnomini
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