8,465 research outputs found
Capital Gains Realizations of the Rich and Sophisticated
This paper attempts to bring theoretical and empirical research on capital gains realization behavior closer together by considering whether investors who appear to engage more in strategic tax avoidance activity also respond differently to tax rates. We find that such investors exhibit significantly smaller responses to permanent tax rate changes than other investors. Put another way, a larger part of their response to capital gains tax rates reflects timing, consistent with their closer adherence to tax avoidance strategies emphasizing arbitrage based on tax rate differentials. This finding holds for two alternative specifications of realization behavior, one of which suggests larger permanent responses to capital gains tax rates than those of previous panel studies.
Tax Loss Carryforwards and Corporate Tax Incentives
This paper investigates the extent to which loss-offset constraints affect corporate tax incentives. Using data gathered from corporate annual reports, we estimate that in 1984 fifteen percent of the firms in the nonfinancial corporate sector had tax loss carryforwards. When weighted by their market value, however, these firms account for less than three percent of this sector, suggesting that loss carryforwards are concentrated among small firms and affect relatively few large corporations. For those firms with loss carryforwards, however, the incentive effects of the corporate income tax may differ significantly from those facing taxable firms. We demonstrate this by calculating the effective tax rates on equipment and structures for both types of firms. Our results suggest that firms which are currently taxable have a substantially greater incentive for equipment investment than firms with loss carryforwards, but that loss carryforwards have a relatively smaller effect on the tax incentive for investing in structures. Overall, firms with loss carryforwards receive a smaller investment stimulus than taxable firms.
Effective Hamiltonian for fermions in an optical lattice across Feshbach resonance
We derive the Hamiltonian for cold fermionic atoms in an optical lattice
across a broad Feshbach resonance, taking into account of both multiband
occupations and neighboring-site collisions. Under typical configurations, the
resulting Hamiltonian can be dramatically simplified to an effective
single-band model, which describes a new type of resonance between the local
dressed molecules and the valence bond states of fermionic atoms at neighboring
sites. On different sides of such a resonance, the effective Hamiltonian is
reduced to either a t-J model for the fermionic atoms or an XXZ model for the
dressed molecules. The parameters in these models are experimentally tunable in
the full range, which allows for observation of various phase transitions.Comment: 5 pages, 2 figure
Approximation and geometric modeling with simplex B-splines associated with irregular triangles
Bivariate quadratic simplical B-splines defined by their corresponding set of knots derived from a (suboptimal) constrained Delaunay triangulation of the domain are employed to obtain a C1-smooth surface. The generation of triangle vertices is adjusted to the areal distribution of the data in the domain. We emphasize here that the vertices of the triangles initially define the knots of the B-splines and do generally not coincide with the abscissae of the data. Thus, this approach is well suited to process scattered data.\ud
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With each vertex of a given triangle we associate two additional points which give rise to six configurations of five knots defining six linearly independent bivariate quadratic B-splines supported on the convex hull of the corresponding five knots.\ud
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If we consider the vertices of the triangulation as threefold knots, the bivariate quadratic B-splines turn into the well known bivariate quadratic Bernstein-Bézier-form polynomials on triangles. Thus we might be led to think of B-splines as of smoothed versions of Bernstein-Bézier polynomials with respect to the entire domain. From the degenerate Bernstein-Bézier situation we deduce rules how to locate the additional points associated with each vertex to establish knot configurations that allow the modeling of discontinuities of the function itself or any of its directional derivatives. We find that four collinear knots out of the set of five defining an individual quadratic B-spline generate a discontinuity in the surface along the line they constitute, and that analogously three collinear knots generate a discontinuity in a first derivative.\ud
Finally, the coefficients of the linear combinations of normalized simplicial B-splines are visualized as geometric control points satisfying the convex hull property.\ud
Thus, bivariate quadratic B-splines associated with irregular triangles provide a great flexibility to approximate and model fast changing or even functions with any given discontinuities from scattered data.\ud
An example for least squares approximation with simplex splines is presented
Domain Patterns in the Microwave-Induced Zero-Resistance State
It has been proposed that the microwave-induced ``zero-resistance''
phenomenon, observed in a GaAs two-dimensional electron system at low
temperatures in moderate magnetic fields, results from a state with multiple
domains, in which a large local electric field \bE(\br) is oriented in
different directions. We explore here the questions of what may determine the
domain arrangement in a given sample, what do the domains look like in
representative cases, and what may be the consequences of domain-wall
localization on the macroscopic dc conductance. We consider both effects of
sample boundaries and effects of disorder, in a simple model, which has a
constant Hall conductivity, and is characterized by a Lyapunov functional.Comment: 19 pages, 5 figures; submitted to a special issue of Journal of
Statistical Physics, in honor of P. C. Hohenberg and J. S. Lange
Quantum phase transitions in the Fermi-Bose Hubbard model
We propose a multi-band Fermi-Bose Hubbard model with on-site fermion-boson
conversion and general filling factor in three dimensions. Such a Hamiltonian
models an atomic Fermi gas trapped in a lattice potential and subject to a
Feshbach resonance. We solve this model in the two state approximation for
paired fermions at zero temperature. The problem then maps onto a coupled
Heisenberg spin model. In the limit of large positive and negative detuning,
the quantum phase transitions in the Bose Hubbard and Paired-Fermi Hubbard
models are correctly reproduced. Near resonance, the Mott states are given by a
superposition of the paired-fermion and boson fields and the Mott-superfluid
borders go through an avoided crossing in the phase diagram.Comment: 4 pages, 3 figure
Effective single-band models for strongly interacting fermions in an optical lattice
To test effective Hamiltonians for strongly interacting fermions in an
optical lattice, we numerically find the energy spectrum for two fermions
interacting across a Feshbach resonance in a double well potential. From the
spectrum, we determine the range of detunings for which the system can be
described by an effective lattice model, and how the model parameters are
related to the experimental parameters. We find that for a range of strong
interactions the system is well described by an effective model, and the
effective superexchange term, , can be smoothly tuned through zero on either
side of unitarity. Right at and around unitarity, an effective one-band general
Hubbard model is appropriate, with a finite and small on-site energy, due to a
lattice-induced anharmonic coupling between atoms at the scattering threshold
and a weakly bound Feshbach molecule in an excited center of mass state.Comment: 7 pages, 7 figures; minor typos correcte
Fractional Quantum Hall Effect and Featureless Mott Insulators
We point out and explicitly demonstrate a close connection that exists
between featureless Mott insulators and fractional quantum Hall liquids. Using
magnetic Wannier states as the single-particle basis in the lowest Landau level
(LLL), we demonstrate that the Hamiltonian of interacting bosons in the LLL
maps onto a Hamiltonian of a featureless Mott insulator on triangular lattice,
formed by the magnetic Wannier states. The Hamiltonian is remarkably simple and
consists only of short-range repulsion and ring-exchange terms.Comment: 7 pages, 1 figure. Published version
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