5,362 research outputs found
Neutron spin-echo study of the critical dynamics of spin-5/2 antiferromagnets in two and three dimensions
We report a neutron spin-echo study of the critical dynamics in the
antiferromagnets MnF and RbMnF with three-dimensional (3D) and
two-dimensional (2D) spin systems, respectively, in zero external field. Both
compounds are Heisenberg antiferromagnets with a small uniaxial anisotropy
resulting from dipolar spin-spin interactions, which leads to a crossover in
the critical dynamics close to the N\'eel temperature, . By taking
advantage of the energy resolution of the spin-echo
spectrometer, we have determined the dynamical critical exponents for both
longitudinal and transverse fluctuations. In MnF, both the characteristic
temperature for crossover from 3D Heisenberg to 3D Ising behavior and the
exponents in both regimes are consistent with predictions from the
dynamical scaling theory. The amplitude ratio of longitudinal and transverse
fluctuations also agrees with predictions. In RbMnF, the critical
dynamics crosses over from the expected 2D Heisenberg behavior for
to a scaling regime with exponent , which has not been predicted
by theory and may indicate the influence of long-range dipolar interactions
Not so far east? The impact of Central-Eastern European imports on the Brexit referendum
We explore the effect of the UK’s economic links with Central-Eastern Europe and China in the case of the Brexit referendum. First, we replicate and independently verify the Colantone and Stanig findings (2018a) on the effect of globalization on Brexit. Then, we extend their original analysis and demonstrate that although both Chinese and Central-Eastern European imports were significant causal determinants of the referendum’s outcome, exposure to Central-Eastern European imports was up to three times more important than exposure to Chinese imports. This may be due to cultural correlates of trade. Our analysis reveals that differences in media coverage between Central-Eastern European and Chinese economic news, as well as migrant population shares from these two regions, might have played a decisive role. Overall, the article also suggests that the import-shock method, as currently applied in the literature, is ill-suited to compare shocks with diverse origins
Regulating Access to Adult Content (with Privacy Preservation)
In the physical world we have well-established mechanisms for keeping children out of adult-only areas. In the virtual world this is generally replaced by self declaration. Some service providers resort to using heavy-weight identification mechanisms, judging adulthood as a side effect thereof. Collection of identification data arguably constitutes an unwarranted privacy invasion in this context, if carried out merely to perform adulthood estimation. This paper presents a mechanism that exploits the adult's more extensive exposure to public media, relying on the likelihood that they will be able to recall details if cued by a carefully chosen picture. We conducted an online study to gauge the viability of this scheme. With our prototype we were able to predict that the user was a child 99% of the time. Unfortunately the scheme also misclassified too many adults. We discuss our results and suggest directions for future research
Cellular automata and Lyapunov exponents
In this article we give a new definition of some analog of Lyapunov exponents
for cellular automata . Then for a shift ergodic and cellular automaton
invariant probability measure we establish an inequality between the entropy of
the automaton, the entropy of the shift and the Lyapunov exponent
Observable Optimal State Points of Sub-additive Potentials
For a sequence of sub-additive potentials, Dai [Optimal state points of the
sub-additive ergodic theorem, Nonlinearity, 24 (2011), 1565-1573] gave a method
of choosing state points with negative growth rates for an ergodic dynamical
system. This paper generalizes Dai's result to the non-ergodic case, and proves
that under some mild additional hypothesis, one can choose points with negative
growth rates from a positive Lebesgue measure set, even if the system does not
preserve any measure that is absolutely continuous with respect to Lebesgue
measure.Comment: 16 pages. This work was reported in the summer school in Nanjing
University. In this second version we have included some changes suggested by
the referee. The final version will appear in Discrete and Continuous
Dynamical Systems- Series A - A.I.M. Sciences and will be available at
http://aimsciences.org/journals/homeAllIssue.jsp?journalID=
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