31,239 research outputs found
Stein factors for negative binomial approximation in Wasserstein distance
The paper gives the bounds on the solutions to a Stein equation for the
negative binomial distribution that are needed for approximation in terms of
the Wasserstein metric. The proofs are probabilistic, and follow the approach
introduced in Barbour and Xia (Bernoulli 12 (2006) 943-954). The bounds are
used to quantify the accuracy of negative binomial approximation to parasite
counts in hosts. Since the infectivity of a population can be expected to be
proportional to its total parasite burden, the Wasserstein metric is the
appropriate choice.Comment: Published at http://dx.doi.org/10.3150/14-BEJ595 in the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Radiance and Doppler shift distributions across the network of the quiet Sun
The radiance and Doppler-shift distributions across the solar network provide
observational constraints of two-dimensional modeling of transition-region
emission and flows in coronal funnels. Two different methods, dispersion plots
and average-profile studies, were applied to investigate these distributions.
In the dispersion plots, we divided the entire scanned region into a bright and
a dark part according to an image of Fe xii; we plotted intensities and Doppler
shifts in each bin as determined according to a filtered intensity of Si ii. We
also studied the difference in height variations of the magnetic field as
extrapolated from the MDI magnetogram, in and outside network. For the
average-profile study, we selected 74 individual cases and derived the average
profiles of intensities and Doppler shifts across the network. The dispersion
plots reveal that the intensities of Si ii and C iv increase from network
boundary to network center in both parts. However, the intensity of Ne viii
shows different trends, namely increasing in the bright part and decreasing in
the dark part. In both parts, the Doppler shift of C iv increases steadily from
internetwork to network center. The average-profile study reveals that the
intensities of the three lines all decline from the network center to
internetwork region. The binned intensities of Si ii and Ne viii have a good
correlation. We also find that the large blue shift of Ne viii does not
coincide with large red shift of C iv. Our results suggest that the network
structure is still prominent at the layer where Ne viii is formed in the quiet
Sun, and that the magnetic structures expand more strongly in the dark part
than in the bright part of this quiet Sun region.Comment: 10 pages,9 figure
Fermi surface topology and low-lying quasiparticle structure of magnetically ordered Fe1+xTe
We report the first photoemission study of Fe1+xTe - the host compound of the
newly discovered iron-chalcogenide superconductors. Our results reveal a pair
of nearly electron- hole compensated Fermi pockets, strong Fermi velocity
renormalization and an absence of a spin-density-wave gap. A shadow hole pocket
is observed at the "X"-point of the Brillouin zone which is consistent with a
long-range ordered magneto-structural groundstate. No signature of Fermi
surface nesting instability associated with Q= pi(1/2, 1/2) is observed. Our
results collectively reveal that the Fe1+xTe series is dramatically different
from the undoped phases of the high Tc pnictides and likely harbor unusual
mechanism for superconductivity and quantum magnetic order.Comment: 5 pages, 4 Figures; Submitted to Phys. Rev. Lett. (2009
Charge collective modes in an incommensurately modulated cuprate
We report the first measurement of collective charge modes of insulating
Sr14Cu24O41 using inelastic resonant x-ray scattering over the complete
Brillouin zone. Our results show that the intense excitation modes at the
charge gap edge predominantly originate from the ladder-containing planar
substructures. The observed ladder modes (E vs. Q) are found to be dispersive
for momentum transfers along the "legs" but nearly localized along the "rungs".
Dispersion and peakwidth characteristics are similar to the charge spectrum of
1D Mott insulators, and we show that our results can be understood in the
strong coupling limit (U >> t_{ladder}> t_{chain}). The observed behavior is in
marked contrast to the charge spectrum seen in most two dimensional cuprates.
Quite generally, our results also show that momentum-tunability of inelastic
scattering can be used to resolve mode contributions in multi-component
incommensurate systems.Comment: 4+ pages, 5 figure
Observation of the Presuperfluid Regime in a Two-Dimensional Bose Gas
In complementary images of coordinate-space and momentum-space density in a
trapped 2D Bose gas, we observe the emergence of pre-superfluid behavior. As
phase-space density increases toward degenerate values, we observe a
gradual divergence of the compressibility from the value predicted by
a bare-atom model, . grows to 1.7 before
reaches the value for which we observe the sudden emergence of a spike
at in momentum space. Momentum-space images are acquired by means of a 2D
focusing technique. Our data represent the first observation of non-meanfield
physics in the pre-superfluid but degenerate 2D Bose gas.Comment: Replace with the version appeared in PR
Emergence of Fermi pockets in an excitonic CDW melted novel superconductor
A superconducting (SC) state (Tc ~ 4.2K) has very recently been observed upon
successful doping of the CDW ordered triangular lattice TiSe, with copper.
Using high resolution photoemission spectroscopy we identify, for the first
time, the momentum space locations of the doped electrons that form the Fermi
sea of the parent superconductor. With doping, we find that the kinematic
nesting volume increases whereas the coherence of the CDW order sharply drops.
In the superconducting doping, we observe the emergence of a large density of
states in the form of a narrow electron pocket near the \textit{L}-point of the
Brillouin Zone with \textit{d}-like character. The \textit{k}-space electron
distributions highlight the unconventional interplay of CDW to SC cross-over
achieved through non-magnetic copper doping.Comment: 4+ pages, 5 figures; Accepted for publication in Phys. Rev. Lett.
(2007
Confinement induced resonances in anharmonic waveguides
We develop the theory of anharmonic confinement-induced resonances (ACIR).
These are caused by anharmonic excitation of the transverse motion of the
center of mass (COM) of two bound atoms in a waveguide. As the transverse
confinement becomes anisotropic, we find that the COM resonant solutions split
for a quasi-1D system, in agreement with recent experiments. This is not found
in harmonic confinement theories. A new resonance appears for repulsive
couplings () for a quasi-2D system, which is also not seen with
harmonic confinement. After inclusion of anharmonic energy corrections within
perturbation theory, we find that these ACIR resonances agree extremely well
with anomalous 1D and 2D confinement induced resonance positions observed in
recent experiments. Multiple even and odd order transverse ACIR resonances are
identified in experimental data, including up to N=4 transverse COM quantum
numbers.Comment: 16 pages,6 fugure
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