9,691 research outputs found
Geography and Intra-National Home Bias: U.S. Domestic Trade in 1949 and 2007
This article examines home bias in U.S. domestic trade in 1949 and 2007. We use a unique data set of 1949 carload waybill statistics produced by the Interstate Commerce Commission, and 2007 Commodity Flow Survey data. The results show that home bias was considerably smaller in 1949 than in 2007 and that home bias in 1949 was even negative for several commodities. We argue that the difference between the geographical distribution of the manufacturing activities in 1949 and that of 2007 is an important factor explaining the differences in the magnitudes of home-bias estimates in those years
On identities in the products of group varieties
Let be the variety of groups satisfying the law . It is
proved that for every sufficiently large prime , say , the
product cannot be defined by a finite set of identities.
This solves the problem formulated by C.K. Gupta and A.N. Krasilnikov in 2003.
We also find the axiomatic and the basis ranks of the variety . For this goal, we improve the estimate for the basis rank of the product
of group varieties obtained by G. Baumslag, B.H. Neumann, H. Neumann and P.M.
Neumann long ago.Comment: 9 page
Edge diffraction of a convergent wave
Closed-form solutions have been derived for the diffraction patterns at the focal plane of (1) a convergent wave of unit amplitude illuminating a segment of a circular aperture and (2) a convergent wave of Gaussian amplitude diffracted by an infinite edge. Photographs showing the main features of these edge transform patterns are presented together with computer-generated graphs
Supersymmetry and Wrapped Branes in Microstate Geometries
We consider the supergravity back-reaction of M2 branes wrapping around the
space-time cycles in 1/8-BPS microstate geometries. We show that such brane
wrappings will generically break all the supersymmetries. In particular, all
the supersymmetries will be broken if there are such wrapped branes but the net
charge of the wrapped branes is zero. We show that if M2 branes wrap a single
cycle, or if they wrap a several of co-linear cycles with the same orientation,
then the solution will be 1/16-BPS, having two supersymmetries. We comment on
how these results relate to using W-branes to understand the microstate
structure of 1/8-BPS black holes.Comment: 20 page
BPS equations and Non-trivial Compactifications
We consider the problem of finding exact, eleven-dimensional, BPS
supergravity solutions in which the compactification involves a non-trivial
Calabi-Yau manifold, , as opposed to simply a . Since there are
no explicitly-known metrics on non-trivial, compact Calabi-Yau manifolds, we
use a non-compact "local model" and take the compactification manifold to be
where is a
hyper-K\"ahler, Gibbons-Hawking ALE space. We focus on backgrounds with three
electric charges in five dimensions and find exact families of solutions to the
BPS equations that have the same four supersymmetries as the three-charge black
hole. Our exact solution to the BPS system requires that the Calabi-Yau
manifold be fibered over the space-time using compensators on . The
role of the compensators is to ensure smoothness of the eleven-dimensional
metric when the moduli of depend on the space-time. The Maxwell
field Ansatz also implicitly involves the compensators through the frames of
the fibration. We examine the equations of motion and discuss the brane
distributions on generic internal manifolds that do not have enough symmetry to
allow smearing.Comment: 32 pages, no figure
On the quasi-isometric rigidity of graphs of surface groups
Let be a word hyperbolic group with a cyclic JSJ decomposition that
has only rigid vertex groups, which are all fundamental groups of closed
surface groups. We show that any group quasi-isometric to is
abstractly commensurable with .Comment: 54 pages, 10 figures, comments welcom
Perturbation of Burkholder's martingale transform and Monge--Amp\`ere equation
Let be a complex martingale difference in
where and \{\e_k\}_{k \geq 0} a sequence in We
obtain the following generalization of Burkholder's famous result. If and then
|\sum_{k=0}^n{(\{c} \e_k \tau) d_k}|_{L^p([0,1], \C^2)} \leq ((p^*-1)^2 +
\tau^2)^{\frac 12}|\sum_{k=0}^n{d_k}|_{L^p([0,1], \C)},
where is sharp and For the result is also true with sharp
constant for Comment: 45 pages, 13 figure
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