1,100 research outputs found
Perceiving through the lens of native phonetics: Italian and Danish listeners\u27 perception of English consonant contrasts
This study examined how the phonetic details of the phonological systems for two different native-language listener groups interact with their perception of the phonetic details of three non-native consonant contrasts. Current theoretical models of cross-language and second language speech perception are evaluated by relating native Italian and native Danish listeners\u27 perceptual assimilation of audio tokens of English /b v w ?/1 to how well the two groups discriminate the corresponding English contrasts /b/-/v/, /w/-/v/, and /?/-/v/. Results indicate some support for the models, but also performance differences between the groups that are unexpected by any existing models. Implications for existing hypotheses about non-native speech perception are discussed
Structure of boson systems beyond the mean-field
We investigate systems of identical bosons with the focus on two-body
correlations. We use the hyperspherical adiabatic method and a decomposition of
the wave function in two-body amplitudes. An analytic parametrization is used
for the adiabatic effective radial potential. We discuss the structure of a
condensate for arbitrary scattering length. Stability and time scales for
various decay processes are estimated. The previously predicted Efimov-like
states are found to be very narrow. We discuss the validity conditions and
formal connections between the zero- and finite-range mean-field
approximations, Faddeev-Yakubovskii formulation, Jastrow ansatz, and the
present method. We compare numerical results from present work with mean-field
calculations and discuss qualitatively the connection with measurements.Comment: 26 pages, 6 figures, submitted to J. Phys. B. Ver. 2 is 28 pages with
modified figures and discussion
Two-body correlations in Bose condensates
We formulate a method to study two-body correlations in a condensate of N
identical bosons. We use the adiabatic hyperspheric approach and assume a
Faddeev like decomposition of the wave function. We derive for a fixed
hyperradius an integro-differential equation for the angular eigenvalue and
wave function. We discuss properties of the solutions and illustrate with
numerical results. The interaction energy is for N~20 five times smaller than
that of the Gross-Pitaevskii equation
Ferromagnetic Kondo-Lattice Model
We present a many-body approach to the electronic and magnetic properties of
the (multiband) Kondo-lattice model with ferromagnetic interband exchange. The
coupling between itinerant conduction electrons and localized magnetic moments
leads, on the one hand, to a distinct temperature-dependence of the electronic
quasiparticle spectrum and, on the other hand, to magnetic properties, as
e.~g.the Curie temperature T_C or the magnon dispersion, which are strongly
influenced by the band electron selfenergy and therewith in particular by the
carrier density. We present results for the single-band Kondo-lattice model in
terms of quasiparticle densities of states and quasiparticle band structures
and demonstrate the density-dependence of the self-consistently derived Curie
temperature. The transition from weak-coupling (RKKY) to strong-coupling
(double exchange) behaviour is worked out.
The multiband model is combined with a tight-binding-LMTO bandstructure
calculation to describe real magnetic materials. As an example we present
results for the archetypal ferromagnetic local-moment systems EuO and EuS. The
proposed method avoids the double counting of relevant interactions and takes
into account the correct symmetry of atomic orbitals.Comment: 15 pages, 10 figure
A Comparison of Outflow Properties in AGN Dwarfs vs. Star Forming Dwarfs
Feedback likely plays a crucial role in resolving discrepancies between
observed and theoretical predictions of dwarf galaxy properties. Stellar
feedback was once believed to be sufficient to explain these discrepancies, but
it has thus far failed to fully reconcile theory and observations. The recent
discovery of energetic galaxy-wide outflows in dwarf galaxies hosting Active
Galactic Nuclei (AGN) suggests that AGN feedback may have a larger role in the
evolution of dwarf galaxies than previously suspected. In order to assess the
relative importance of stellar versus AGN feedback in these galaxies, we
perform a detailed Keck/KCWI optical integral field spectroscopic study of a
sample of low-redshift star-forming (SF) dwarf galaxies that show outflows in
ionized gas in their SDSS spectra. We characterize the outflows and compare
them to observations of AGN-driven outflows in dwarfs. We find that SF dwarfs
have outflow components that have comparable widths (W) to those of
outflows in AGN dwarfs, but are much less blue-shifted, indicating that SF
dwarfs have significantly slower outflows than their AGN counterparts. The
outflows in SF dwarfs are spatially resolved and significantly more extended
than those in AGN dwarfs. The mass loss rates, momentum and energy rates of
SF-driven outflows are much lower than those of AGN-driven outflows. Our
results indicate that AGN feedback in the form of gas outflows may play an
important role in dwarf galaxies and should be considered along with SF
feedback in models of dwarf galaxy evolution.Comment: 27 pages, 25 figures, Accepted for publication in Ap
Correlated N-boson systems for arbitrary scattering length
We investigate systems of identical bosons with the focus on two-body
correlations and attractive finite-range potentials. We use a hyperspherical
adiabatic method and apply a Faddeev type of decomposition of the wave
function. We discuss the structure of a condensate as function of particle
number and scattering length. We establish universal scaling relations for the
critical effective radial potentials for distances where the average distance
between particle pairs is larger than the interaction range. The correlations
in the wave function restore the large distance mean-field behaviour with the
correct two-body interaction. We discuss various processes limiting the
stability of condensates. With correlations we confirm that macroscopic
tunneling dominates when the trap length is about half of the particle number
times the scattering length.Comment: 15 pages (RevTeX4), 11 figures (LaTeX), submitted to Phys. Rev. A.
Second version includes an explicit comparison to N=3, a restructured
manuscript, and updated figure
Softening and Broadening of the Zone Boundary Magnons in Pr0.63Sr0.37MnO3
We have studied the spin dynamics in PrSrMnO above and
below the Curie temperature K. Three distinct new features have been
observed: a softening of the magnon dispersion at the zone boundary for
, significant broadening of the zone boundary magnons as , and
no evidence for residual spin-wave like excitations just above . The
results are inconsistent with double exchange models that have been
successfully applied to higher samples, indicating an evolution of the
spin system with decreasing .Comment: 12 pages, Latex, 3 figure
Dynamical response of a Bose-Einstein condensate to a discontinuous change in internal state
A two-photon transition is used to convert an arbitrary fraction of the 87Rb
atoms in a |F=1,m_f=-1> condensate to the |F=2,m_f=1> state. Transferring the
entire population imposes a discontinuous change on the condensate's mean-field
repulsion, which leaves a residual ringing in the condensate width. A
calculation based on Gross-Pitaevskii theory agrees well with the observed
behavior, and from the comparison we obtain the ratio of the intraspecies
scattering lengths for the two states, a_|1,-1> / a_|2,1> = 1.062(12).Comment: 4 pages, 3 figure
Two-body correlations in N-body boson systems
We formulate a method to study two-body correlations in a system of N
identical bosons interacting via central two-body potentials. We use the
adiabatic hyperspherical approach and assume a Faddeev-like decomposition of
the wave function. For a fixed hyperradius we derive variationally an optimal
integro-differential equation for hyperangular eigenvalue and wave function.
This equation reduces substantially by assuming the interaction range much
smaller than the size of the N-body system. At most one-dimensional integrals
then remain. We view a Bose-Einstein condensate pictorially as a structure in
the landscape of the potential given as a function of the one-dimensional
hyperradial coordinate. The quantum states of the condensate can be located in
one of the two potential minima. We derive and discuss properties of the
solutions and illustrate with numerical results. The correlations lower the
interaction energy substantially. The new multi-body Efimov states are
solutions independent of details of the two-body potential. We compare with
mean-field results and available experimental data.Comment: 19 pages (RevTeX4), 13 figures (latex). Journal-link:
http://pra.aps.org
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