14,030 research outputs found
China's Embrace of Globalization
As China has become an increasingly important part of the global trading system over the past two decades, interest in the country and its international economic policies has increased among international economists who are not China specialists. This paper represents an attempt to provide the international economics community with a succinct summary of the major steps in the evolution of Chinese policy toward international trade and foreign direct investment and their consequences since the late 1970s. In doing so, we draw upon and update a number of more comprehensive book-length treatments of the subject. It is our hope that this paper will prove to be a useful resource for the growing numbers of international economists who are exploring China-related issues, either in the classroom or in their own research.
The Rise of a Magnetic Flux Tube in a Background Field: Solar Helicity Selection Rules
The buoyant transport of magnetic fields from the solar interior towards the
surface plays an important role in the emergence of active regions, the
formation of sunspots and the overall solar dynamo. Observations suggest that
toroidal flux concentrations often referred to as "flux tubes", rise from their
region of initiation likely in the solar tachocline towards the solar surface
due to magnetic buoyancy. Many studies have assumed the existence of such
magnetic structures and studied the buoyant rise of an isolated flux tube in a
quiescent, field-free environment. Here, motivated by their formation (Cline et
al. 2003; Brummell et al. 2002), we relax the latter assumption and study the
rise of a toroidal flux tube embedded in a large-scale poloidal background
magnetic field. We find that the presence of the large-scale background field
severely affects the dynamics of the rising tube. A relatively weak background
field, as low as 6% of the tube strength, can destroy the rise of a tube that
would otherwise rise in the absence of the background field. Surprisingly, the
rise of tubes with one sign of the twist is suppressed by a significantly
weaker background field than the other. This demonstrates a potential mechanism
for the selection of the preferred helicity of rising and emerging tubes for
the solar case that is commensurate with many features of the hemispherical
rule.Comment: 9 pages, 5 figures, accepted for publication in ApJ
Constructing Reference Metrics on Multicube Representations of Arbitrary Manifolds
Reference metrics are used to define the differential structure on multicube
representations of manifolds, i.e., they provide a simple and practical way to
define what it means globally for tensor fields and their derivatives to be
continuous. This paper introduces a general procedure for constructing
reference metrics automatically on multicube representations of manifolds with
arbitrary topologies. The method is tested here by constructing reference
metrics for compact, orientable two-dimensional manifolds with genera between
zero and five. These metrics are shown to satisfy the Gauss-Bonnet identity
numerically to the level of truncation error (which converges toward zero as
the numerical resolution is increased). These reference metrics can be made
smoother and more uniform by evolving them with Ricci flow. This smoothing
procedure is tested on the two-dimensional reference metrics constructed here.
These smoothing evolutions (using volume-normalized Ricci flow with DeTurck
gauge fixing) are all shown to produce reference metrics with constant scalar
curvatures (at the level of numerical truncation error).Comment: 37 pages, 16 figures; additional introductory material added in
version accepted for publicatio
Scalar, Vector and Tensor Harmonics on the Three-Sphere
Scalar, vector and tensor harmonics on the three-sphere were introduced
originally to facilitate the study of various problems in gravitational
physics. These harmonics are defined as eigenfunctions of the covariant Laplace
operator which satisfy certain divergence and trace identities, and
ortho-normality conditions. This paper provides a summary of these properties,
along with a new notation that simplifies and clarifies some of the key
expressions. Practical methods are described for accurately and efficiently
computing these harmonics numerically, and test results are given that
illustrate how well the analytical identities are satisfied by the harmonics
computed numerically in this way.Comment: 14 pages, 9 figures, to appear in General Relativity and Gravitatio
More on the covariant retarded Green's function for the electromagnetic field in de Sitter spacetime
In a recent paper (Phys. Rev. D78, 084031 (2008), arXiv:0808.0642, Ref. [1])
it was shown in examples that the covariant retarded Green's functions in
particular gauges for electromagnetism and linearized gravity can be used to
reproduce field configurations correctly in spite of the spacelike nature of
past infinity in de Sitter spacetime. In this paper we extend the work of Ref.
[1] concerning the electromagnetic field and show that the covariant retarded
Green's function with an arbitrary value of the gauge parameter reproduces the
electromagnetic field from two opposite charges at antipodal points of de
Sitter spacetime.Comment: 4 pages, addendum to PRD 78, 084031 (2008) [arXiv:0808.0642
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