26,030 research outputs found
The effect of magnetic dipolar interactions on the interchain spin wave dispersion in CsNiF_3
Inelastic neutron scattering measurements were performed on the ferromagnetic
chain system CsNiF_3 in the collinear antiferromagnetic ordered state below T_N
= 2.67K. The measured spin wave dispersion was found to be in good agreement
with linear spin wave theory including dipolar interactions. The additional
dipole tensor in the Hamiltonian was essential to explain some striking
phenomena in the measured spin wave spectrum: a peculiar feature of the
dispersion relation is a jump at the zone center, caused by strong dipolar
interactions in this system. The interchain exchange coupling constant and the
planar anisotropy energy were determined within the present model to be J'/k_B
= -0.0247(12)K and A/k_B = 3.3(1)K. This gives a ratio J/J' \approx 500, using
the previously determined intrachain coupling constant J/k_B = 11.8$. The small
exchange energy J' is of the same order as the dipolar energy, which implies a
strong competition between the both interactions.Comment: 18 pages, TeX type, 7 Postscript figures included. To be published in
Phys. Rev.
Rational self-affine tiles
An integral self-affine tile is the solution of a set equation , where
is an integer matrix and is a finite
subset of . In the recent decades, these objects and the induced
tilings have been studied systematically. We extend this theory to matrices
. We define rational self-affine tiles
as compact subsets of the open subring of the ad\'ele ring , where the factors of the
(finite) product are certain -adic completions of a number field
that is defined in terms of the characteristic polynomial of .
Employing methods from classical algebraic number theory, Fourier analysis in
number fields, and results on zero sets of transfer operators, we establish a
general tiling theorem for these tiles. We also associate a second kind of
tiles with a rational matrix. These tiles are defined as the intersection of a
(translation of a) rational self-affine tile with . Although these intersection
tiles have a complicated structure and are no longer self-affine, we are able
to prove a tiling theorem for these tiles as well. For particular choices of
digit sets, intersection tiles are instances of tiles defined in terms of shift
radix systems and canonical number systems. Therefore, we gain new results for
tilings associated with numeration systems
Predicting Mercury's Precession using Simple Relativistic Newtonian Dynamics
We present a new simple relativistic model for planetary motion describing
accurately the anomalous precession of the perihelion of Mercury and its
origin. The model is based on transforming Newton's classical equation for
planetary motion from absolute to real spacetime influenced by the
gravitational potential and introducing the concept of influenced direction.Comment: 5 page
Constraints on the Symmetry Energy Using the Mass-Radius Relation of Neutron Stars
The nuclear symmetry energy is intimately connected with nuclear
astrophysics. This contribution focuses on the estimation of the symmetry
energy from experiment and how it is related to the structure of neutron stars.
The most important connection is between the radii of neutron stars and the
pressure of neutron star matter in the vicinity of the nuclear saturation
density . This pressure is essentially controlled by the nuclear symmetry
energy parameters and , the first two coefficients of a Taylor
expansion of the symmetry energy around . We discuss constraints on these
parameters that can be found from nuclear experiments. We demonstrate that
these constraints are largely model-independent by deriving them qualitatively
from a simple nuclear model. We also summarize how recent theoretical studies
of pure neutron matter can reinforce these constraints. To date, several
different astrophysical measurements of neutron star radii have been attempted.
Attention is focused on photospheric radius expansion bursts and on thermal
emissions from quiescent low-mass X-ray binaries. While none of these
observations can, at the present time, determine individual neutron star radii
to better than 20% accuracy, the body of observations can be used with Bayesian
techniques to effectively constrain them to higher precision. These techniques
invert the structure equations and obtain estimates of the pressure-density
relation of neutron star matter, not only near , but up to the highest
densities found in neutron star interiors. The estimates we derive for neutron
star radii are in concordance with predictions from nuclear experiment and
theory.Comment: 24 pages, 13 figure
Physics Opportunities with Polarized e- and e+ Beams at TESLA
Beam polarization at e+ e- linear colliders will be a powerful tool for high
precision analyses. Often it is assumed that the full information from
polarization effects is provided by polarization of the electron beam and no
further information can be obtained by the simultaneous polarization of the
positrons. In this paper we point out the advantages of polarizing both beams,
and summarize the polarization-related results of the Higgs, Electroweak, QCD,
SUSY and Alternative Theories working groups of the ECFA/DESY workshop for a
planned linear collider operating in the energy range sqrt{s}= 500-800 GeV.Comment: 36 pages, 21 postscript figures, latex using epsfi
Predicting the relativistic periastron advance of a binary without curving spacetime
Relativistic Newtonian Dynamics, the simple model used previously for
predicting accurately the anomalous precession of Mercury, is now applied to
predict the periastron advance of a binary. The classical treatment of a binary
as a two-body problem is modified to account for the influence of the
gravitational potential on spacetime. Without curving spacetime, the model
predicts the identical equation for the relativistic periastron advance as the
post-Newtonian approximation of general relativity formalism thereby providing
further substantiation of this model.Comment: 6 pages, 2 figure
Income Taxes and Entrepreneurial Choice: Empirical Evidence from Germany
Entrepreneurial activity is often regarded as an engine for economic growth and job creation. Through tax policy, governments possess a potential lever to influence the decisions of economic agents to start and close small businesses. In Germany, the top marginal income tax rates were reduced exclusively for entrepreneurs in 1994 and 1999/2000. These tax reforms provided two naturally defined control groups that enable us to exploit the legislation changes as "natural experiments". First, the tax rate reductions did not apply to freelance professionals (Freiberufler), and second, entrepreneurs with earnings below a certain threshold were not affected. Using data from two different sources, the SOEP and the Mikrozensus (LFS), we analyse the effect of the tax cuts on transitions into and out of self-employment and on the rate of self-employment. We apply a "difference-in-difference-in-difference" estimation technique within a discrete time hazard rate model. The results indicate that the decrease in tax rates did not have a significant effect on the self-employment decision.Taxation, entrepreneurship, natural experiment, difference-in-difference-in-difference estimation
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