1,068 research outputs found
Skyrmions and Hall Transport
We derive a generalized set of Ward identities that captures the effects of
topological charge on Hall transport. The Ward identities follow from the 2+1
dimensional momentum algebra, which includes a central extension proportional
to the topological charge density. In the presence of topological objects like
Skyrmions, we observe that the central term leads to a direct relation between
the thermal Hall conductivity and the topological charge density. We extend
this relation to incorporate the effects of a magnetic field and an electric
current. The topological charge density produces a distinct signature in the
electric Hall conductivity, which is identified in existing experimental data,
and yields further novel predictions. For insulating materials with translation
invariance, the Hall viscosity can be directly determined from the Skyrmion
density and the thermal Hall conductivity to be measured as a function of
momentum.Comment: 6+1 pages including Supplemental Material. Version to appear in
Physical Review Letter
How Productive is Public Capital? A Meta-Analysis
The paper analyzes the contribution of public capital to private output using several meta-analytical techniques. Both fixed and random effects models are estimated by Weighted Least Squares. Sample overlap across studies is explicitly controlled for by employing a ‘full’ Generalized Least Squares estimator. The weighted average output elasticity of public capital amounts to 0.08 after correcting for publication bias. A substantial part of the heterogeneity across studies is explained by study design parameters, such as econometric specification, estimation technique, empirical model, type of public capital, and level of aggregation of public capital data. The large elasticities of public capital found in the early literature seem to be caused by either unidentified (but present) cointegrating relationships or spurious relationships in national time series.public capital, infrastructure, public investment, meta-analysis, meta-regression analysis, publication bias
Non-Relativistic Superstring Theories
We construct a supersymmetric version of the ``critical'' non-relativistic
bosonic string theory\cite{Kim:2007hb} with its manifest global symmetry. We
introduce the anticommuting CFT which is the super partner of the
CFT. The conformal weights of the and fields are both
1/2. The action of the fermionic sector can be transformed into that of the
relativistic superstring theory. We explicitly quantize the theory with
manifest SO(8) symmetry and find that the spectrum is similar to that of Type
IIB superstring theory. There is one notable difference: the fermions are
non-chiral. We further consider ``noncritical'' generalizations of the
supersymmetric theory using the superspace formulation. There is an infinite
range of possible string theories similar to the supercritical string theories.
We comment on the connection between the critical non-relativistic string
theory and the lightlike Linear Dilaton theory.Comment: Typos corrected, references added. A version to appear in Phys. Rev.
Penning trap mass measurements on (99-109)$Cd with ISOLTRAP and implications on the rp process
Penning trap mass measurements on neutron-deficient Cd isotopes (99-109)Cd
have been performed with the ISOLTRAP mass spectrometer at ISOLDE/CERN, all
with relative mass uncertainties below 3*10^8. A new mass evaluation has been
performed. The mass of 99Cd has been determined for the first time which
extends the region of accurately known mass values towards the doubly magic
nucleus 100Sn. The implication of the results on the reaction path of the rp
process in stellar X-ray bursts is discussed. In particular, the uncertainty of
the abundance and the overproduction created by the rp-process for the mass A =
99 is demonstrated by reducing the uncertainty of the proton-separation energy
of 100In Sp(100In) by a factor of 2.5.Comment: 14 pages, 9 figure
On application of Liouville type equations to constructing B\"acklund transformations
It is shown how pseudoconstants of the Liouville-type equations can be
exploited as a tool for construction of the B\"acklund transformations. Several
new examples of such transformations are found. In particular we obtained the
B\"acklund transformations for a pair of three-component analogs of the
dispersive water wave system, and auto-B\"acklund transformations for coupled
three-component KdV-type systems.Comment: 11 pages, no figure
World Sheet Commuting \beta\gamma CFT and Non-Relativistic String Theories
We construct a sigma model in two dimensions with Galilean symmetry in flat
target space similar to the sigma model of the critical string theory with
Lorentz symmetry in 10 flat spacetime dimensions. This is motivated by the
works of Gomis and Ooguri\cite{Gomis:2000bd} and Danielsson et. al.
\cite{Danielsson:2000gi, Danielsson:2000mu}. Our theory is much simpler than
their theory and does not assume a compact coordinate. This non-relativistic
string theory has a bosonic matter CFT with the conformal weight
of as 1. It is natural to identify time as a linear combination of
and through an explicit realization of the Galilean
boost symmetry. The angle between and parametrizes one
parameter family of selection sectors. These selection sectors are responsible
for having a non-relativistic dispersion relation without a nontrivial topology
in the non-relativistic setup, which is one of the major differences from the
previous works\cite{Gomis:2000bd, Danielsson:2000gi, Danielsson:2000mu}. This
simple theory is the non-relativistic analogue of the critical string theory,
and there are many different avenues ahead to be investigated. We mention a
possible consistent generalization of this theory with different conformal
weights for the CFT. We also mention supersymmetric
generalizations of these theories.Comment: 26 page
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Seeing other perspectives: Evaluating the use of virtual and augmented reality to simulate visual impairments (OpenVisSim)
Simulations of visual impairment are often used to educate and inform the public. However, evidence regarding their accuracy remains lacking. Here we evaluated the effectiveness of modern digital technologies to simulate the everyday difficulties caused by glaucoma. Twenty5 three normally-sighted adults performed two everyday tasks that glaucoma patients often report difficulties with: a visual search task in which they attempted to locate a mobile phone in virtual domestic environments (Virtual Reality; VR), and a visual mobility task in which impairments were overlaid onto a real-world environment using Augmented Reality (AR). On some trials, a gaze-contingent simulated scotoma --- generated using perimetric data from a patient with advanced glaucoma --- was presented in either the superior or inferior hemifield. The main outcome measure was task completion time. Eye and head movements were also tracked and used to assess individual differences in looking behaviors. The results showed that the simulated impairments substantial impaired performance in both the VR (visual search) and AR (visual mobility) tasks (both P < 0.001). Furthermore, and in line with previous patient data: impairments were greatest when the simulated VFL was inferior versus superior (P < 0.001), participants made more eye and head movements in the inferior VFL condition (P < 0.001), and participants rated the inferior VFL condition as more difficult (P < 0.001). Notably, the difference in performance between the inferior and superior conditions was almost as great as the difference between a superior VFL and no impairment at all (VR: 71%; AR: 70%). We conclude that modern digital simulators are able to replicate and objectively quantify some of the key everyday difficulties associated with visual impairments. Advantages, limitations and possible applications of current technologies are discussed. Instructions are also given for how to freely obtain the software described (OpenVisSim)
Search for the Radiative Capture d+d->^4He+\gamma Reaction from the dd\mu Muonic Molecule State
A search for the muon catalyzed fusion reaction dd --> ^4He +\gamma in the
dd\mu muonic molecule was performed using the experimental \mu CF installation
TRITON and NaI(Tl) detectors for \gamma-quanta. The high pressure target filled
with deuterium at temperatures from 85 K to 800 K was exposed to the negative
muon beam of the JINR phasotron to detect \gamma-quanta with energy 23.8 MeV.
The first experimental estimation for the yield of the radiative deuteron
capture from the dd\mu state J=1 was obtained at the level n_{\gamma}\leq
2\times 10^{-5} per one fusion.Comment: 9 pages, 3 Postscript figures, submitted to Phys. At. Nuc
Reporting guidelines for meta-analysis in economics
Meta‐analysis has become the conventional approach to synthesizing the results of empirical economics research. To further improve the transparency and replicability of the reported results and to raise the quality of meta‐analyses, the Meta‐Analysis of Economics Research Network has updated the reporting guidelines that were published by this Journal in 2013. Future meta‐analyses in economics will be expected to follow these updated guidelines or give valid reasons why a meta‐analysis should deviate from them
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