16,963 research outputs found
Coexisting chaotic and multi-periodic dynamics in a model of cardiac alternans
The spatiotemporal dynamics of cardiac tissue is an active area of research
for biologists, physicists, and mathematicians. Of particular interest is the
study of period-doubling bifurcations and chaos due to their link with cardiac
arrhythmogenesis. In this paper we study the spatiotemporal dynamics of a
recently developed model for calcium-driven alternans in a one dimensional
cable of tissue. In particular, we observe in the cable coexistence of regions
with chaotic and multi-periodic dynamics over wide ranges of parameters. We
study these dynamics using global and local Lyapunov exponents and spatial
trajectory correlations. Interestingly, near nodes -- or phase reversals --
low-periodic dynamics prevail, while away from the nodes the dynamics tend to
be higher-periodic and eventually chaotic. Finally, we show that similar
coexisting multi-periodic and chaotic dynamics can also be observed in a
detailed ionic model
Towards a continuous modeling of natural language domains
Humans continuously adapt their style and language to a variety of domains.
However, a reliable definition of `domain' has eluded researchers thus far.
Additionally, the notion of discrete domains stands in contrast to the
multiplicity of heterogeneous domains that humans navigate, many of which
overlap. In order to better understand the change and variation of human
language, we draw on research in domain adaptation and extend the notion of
discrete domains to the continuous spectrum. We propose representation
learning-based models that can adapt to continuous domains and detail how these
can be used to investigate variation in language. To this end, we propose to
use dialogue modeling as a test bed due to its proximity to language modeling
and its social component.Comment: 5 pages, 3 figures, published in Uphill Battles in Language
Processing workshop, EMNLP 201
Modified teleparallel theories of gravity
We investigate modified theories of gravity in the context of teleparallel
geometries. It is well known that modified gravity models based on the torsion
scalar are not invariant under local Lorentz transformations while
modifications based on the Ricci scalar are. This motivates the study of a
model depending on the torsion scalar and the divergence of the torsion vector.
We derive the teleparallel equivalent of gravity as a particular subset
of these models and also show that this is the unique theory in this class that
is invariant under local Lorentz transformation. Furthermore one can show that
gravity is the unique theory admitting second order field equations.Comment: 9 pages, 1 figure; some typos fixed, slightly improved notatio
Geometrically nonlinear Cosserat elasticity in the plane: applications to chirality
Modelling two-dimensional chiral materials is a challenging problem in
continuum mechanics because three-dimensional theories reduced to isotropic
two-dimensional problems become non-chiral. Various approaches have been
suggested to overcome this problem. We propose a new approach to this problem
by formulating an intrinsically two-dimensional model which does not require
references to a higher dimensional one. We are able to model planar chiral
materials starting from a geometrically non-linear Cosserat type elasticity
theory. Our results are in agreement with previously derived equations of
motion but can contain additional terms due to our non-linear approach. Plane
wave solutions are briefly discussed within this model.Comment: 22 pages, 1 figure; v2 updated versio
New classes of modified teleparallel gravity models
New classes of modified teleparallel theories of gravity are introduced. The
action of this theory is constructed to be a function of the irreducible parts
of torsion , where and are squares of the axial, tensor and vector components
of torsion, respectively. This is the most general (well-motivated) second
order teleparallel theory of gravity that can be constructed from the torsion
tensor. Different particular second order theories can be recovered from this
theory such as new general relativity, conformal teleparallel gravity or
gravity. Additionally, the boundary term which connects the Ricci scalar
with the torsion scalar via can also be incorporated into the action.
By performing a conformal transformation, it is shown that the two unique
theories which have an Einstein frame are either the teleparallel equivalent of
general relativity or gravity, as expected.Comment: v2: 10 pages, accepted for publication in PLB; for a detailed
derivation of the field equations see Appendix A in v
Trends in tariff reforms and trends in wage inequality
The authors provide new evidence on the impacts of trade reforms on wages and wage inequality in developing countries. While most of the current literature on the topic achieves identification by comparing outcomes before and after one episode of trade liberalization across industries, they propose a stronger identifying strategy. The authors explore the recent historical record of policy changes adopted by Argentina: from significant protection in the early 1970s, to the first episode of liberalization during the late 1970s, back to a slowdown of reforms during the 1980s, to the second episode of liberalization in the 1990s. These swings in trade policy comprise broken trends in trade reforms that they can compare with observed trends in wages and wage inequality. After setting up unusual historical data sets of trends in tariffs, trends in wages, and trends in wage inequality, the evidence supports two well-known hypotheses: trade liberalization, other things being equal, (1) has reduced wages, and (2) has increased wage inequality.Free Trade,Economic Theory&Research,Trade Policy,Export Competitiveness,Labor Markets
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