777 research outputs found
Lines in the Sand on the Australian Political Beach
Spatial models of voting behaviour are the dominant paradigm in political science. Consistent with this approach, it will be the case that, ceteris paribus, voters should vote for the party nearest to them on the political spectrum. A key question is how we measure nearness or distance. We investigate this issue by estimating discrete choice models for voting outcomes using the 2001 Australian Election Study survey data. The evidence supports the proposition that it is perceived and not actual distance that performs best. Our findings also suggest that where a voter locates on the political spectrum is almost as good a predictor of their voting outcome as how close they are to the partiesSpatial Competition, Distance Measures, Discrete Choice
Multipole Amplitudes of Pion Photoproduction on Nucleons up to 2GeV within Dispersion Relations and Unitary Isobar Model
Two approaches for analysis of pion photo- and electroproduction on nucleons
in the resonance energy region are checked at using the results of
GWU(VPI) partial-wave analysis of photoproduction data. The approaches are
based on dispersion relations and unitary isobar model. Within dispersion
relations good description of photoproduction multipoles is obtained up to
. Within unitary isobar model, modified with increasing energy by
incorporation of Regge poles, and with unified Breit-Wigner parametrization of
resonance contributions, good description of photoproduction multipoles is
obtained up to .Comment: 23 pages, LaTe
Action-gradient-minimizing pseudo-orbits and almost-invariant tori
Transport in near-integrable, but partially chaotic,
degree-of-freedom Hamiltonian systems is blocked by invariant tori and is
reduced at \emph{almost}-invariant tori, both associated with the invariant
tori of a neighboring integrable system. "Almost invariant" tori with rational
rotation number can be defined using continuous families of periodic
\emph{pseudo-orbits} to foliate the surfaces, while irrational-rotation-number
tori can be defined by nesting with sequences of such rational tori. Three
definitions of "pseudo-orbit," \emph{action-gradient--minimizing} (AGMin),
\emph{quadratic-flux-minimizing} (QFMin) and \emph{ghost} orbits, based on
variants of Hamilton's Principle, use different strategies to extremize the
action as closely as possible. Equivalent Lagrangian (configuration-space
action) and Hamiltonian (phase-space action) formulations, and a new approach
to visualizing action-minimizing and minimax orbits based on AGMin
pseudo-orbits, are presented.Comment: Accepted for publication in a special issue of Communications in
Nonlinear Science and Numerical Simulation (CNSNS) entitled "The mathematical
structure of fluids and plasmas : a volume dedicated to the 60th birthday of
Phil Morrison
Comparison of quantum mechanical and classical trajectory calculations of cross sections for ion-atom impact ionization of negative - and positive -ions for heavy ion fusion applications
Stripping cross sections in nitrogen have been calculated using the classical
trajectory approximation and the Born approximation of quantum mechanics for
the outer shell electrons of 3.2GeV I and Cs ions. A large
difference in cross section, up to a factor of six, calculated in quantum
mechanics and classical mechanics, has been obtained. Because at such high
velocities the Born approximation is well validated, the classical trajectory
approach fails to correctly predict the stripping cross sections at high
energies for electron orbitals with low ionization potential.Comment: submitted to Phys. Rev.
The Role of the D13 (1520) Resonance in eta Electroproduction
We investigate the electroproduction of eta mesons below a center of momentum
energy of 1.6 GeV, with particular emphasis on the roles of the N*(1535) and
N*(1520) resonances. Using the effective Lagrangian approach, we show that the
transverse helicity amplitude of the N*(1535) can be extracted with good
accuracy from the new eta electroproduction data, under reasonable assumptions
for the strength of the longitudinal helicity amplitude. In addition, although
the differential cross section is found to to have a small sensitivity to the
N*(1520) resonance, it is shown that a recently completed double polarization
experiment is very sensitive to this resonance.Comment: 7 pages, Revtex, 3 figure
Property Studies of Alaskan Silts in the Matanuska Valley, Big Delta, and Fairbanks Areas
The study of four Alaskan areas was begun in the summer of 1954 under a program sponsored by the Office of Naval Research. The Iowa State College Engineering Experiment Station directed the study in collaboration with the Department of Geology, Iowa State College. The program was initiated to: 1. Determine the distribution of engineering soil materials m four Alaska areas. 2. Determine the engineering properties and trafficability characteristic; of these materials. 3. Determine the feasibility and best methods of stabilizing these materials for use as road and airfield building material. 4. Further the studies of geology of Alaska. 5. Attempt a correlation of the engineering and geologic properties of the Alaskan materials with similar materials in the Midwest United States
Non-linear doublon production in a Mott insulator --- Landau-Dykhne method applied to an integrable model
Doublon-hole pair production which takes place during dielectric breakdown in
a Mott insulator subject to a strong laser or a static electric field is
studied in the one-dimensional Hubbard model. Two nonlinear effects cause the
excitation, i.e., multi-photon absorption and quantum tunneling. Keldysh
crossover between the two mechanisms occurs as the field strength and photon
energy is changed. The calculation is done analytically by the Landau-Dykhne
method in combination with the Bethe ansatz solution and the results are
compared with those of the time dependent density matrix renormalization group.
Using this method, we calculate distribution function of the generated
doublon-hole pairs and show that it drastically changes as we cross the Keldysh
crossover line. After calculating the tunneling threshold for several
representative one-dimensional Mott insulators, possible experimental tests of
the theory is proposed such as angle resolved photoemission spectroscopy of the
upper Hubbard band in the quantum tunneling regime. We also discuss the
relation of the present theory with a many-body extension of electron-positron
pair production in nonlinear quantum electrodynamics known as the Schwinger
mechanism.Comment: 15 page
Cosmic microwave background and large scale structure limits on the interaction between dark matter and baryons
We study the effect on the cosmic microwave background (CMB) anisotropy and
large scale structure (LSS) power spectrum of a scattering interaction between
cold dark matter and baryons. This scattering alters the CMB anisotropy and LSS
spectrum through momentum transfer between the cold dark matter particles and
the baryons. We find that current CMB observations can put an upper limit on
the scattering cross section which is comparable with or slightly stronger than
previous disk heating constraints at masses greater than 1 GeV, and much
stronger at smaller masses. When large-scale structure constraints are added to
the CMB limits, our constraint is more stringent than this previous limit at
all masses. In particular, a dark matter-baryon scattering cross section
comparable to the ``Spergel-Steinhardt'' cross section is ruled out for dark
matter mass greater than 1 GeV.Comment: 8 pages, 2 figures, use RevTeX4, submitted to PRD replaced with
revised versio
Hard-Loop Effective Action for Anisotropic Plasmas
We generalize the hard-thermal-loop effective action of the equilibrium
quark-gluon plasma to a non-equilibrium system which is space-time homogeneous
but for which the parton momentum distribution is anisotropic. We show that the
manifestly gauge-invariant Braaten-Pisarski form of the effective action can be
straightforwardly generalized and we verify that it then generates all n-point
functions following from collisionless gauge-covariant transport theory for a
homogeneous anisotropic plasma. On the other hand, the Taylor-Wong form of the
hard-thermal-loop effective action has a more complicated generalization to the
anisotropic case. Already in the simplest case of anisotropic distribution
functions, it involves an additional term that is gauge invariant by itself,
but nontrivial also in the static limit.Comment: 12 pages. Version 3: typo in (15) corrected, note added discussing
metric conventions use
Proton-proton bremsstrahlung below and above pion-threshold: the influence of the -isobar
The proton-proton bremsstrahlung is investigated within a coupled-channel
model with the degree of freedom. The model is consistent with the
scattering up to 1 GeV and the vertex determined in the
study of pion photoproduction reactions. It is found that the
excitation can significantly improve the agreements with the at MeV. Predictions at and MeV are
presented for future experimental tests.Comment: 26 pages Revtex, 12 figures are available from the authors upon
request ([email protected]
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