571 research outputs found
Observations of Coronal Mass Ejections with the Coronal Multichannel Polarimeter
The Coronal Multichannel Polarimeter (CoMP) measures not only the
polarization of coronal emission, but also the full radiance profiles of
coronal emission lines. For the first time, CoMP observations provide
high-cadence image sequences of the coronal line intensity, Doppler shift and
line width simultaneously in a large field of view. By studying the Doppler
shift and line width we may explore more of the physical processes of CME
initiation and propagation. Here we identify a list of CMEs observed by CoMP
and present the first results of these observations. Our preliminary analysis
shows that CMEs are usually associated with greatly increased Doppler shift and
enhanced line width. These new observations provide not only valuable
information to constrain CME models and probe various processes during the
initial propagation of CMEs in the low corona, but also offer a possible
cost-effective and low-risk means of space weather monitoring.Comment: 6 figures. Will appear in the special issue of Coronal Magnetism,
Sol. Phy
Phase separation and ferroelectric ordering in charge frustrated LuFe2O4-x
The transmission electron microscopy observations of the charge ordering (CO)
which governs the electronic polarization in LuFe2O4-x clearly show the
presence of a remarkable phase separation at low temperatures. Two CO ground
states are found to adopt the charge modulations of Q1 = (1/3, 1/3, 0) and Q2 =
(1/3 + y, 1/3 + y, 3/2), respectively. Our structural study demonstrates that
the incommensurately Q2-modulated state is chiefly stable in samples with
relatively lower oxygen contents. Data from theoretical simulations of the
diffraction suggest that both Q1- and Q2-modulated phases have ferroelectric
ordering. The effects of oxygen concentration on the phase separation and
electric polarization in this layered system are discussed.Comment: 11 pages, 5 figure
Transition from band insulator to Mott insulator in one dimension: Critical behavior and phase diagram
We report a systematic study of the transition from a band insulator (BI) to
a Mott insulator (MI) in a one-dimensional Hubbard model at half-filling with
an on-site Coulomb interaction U and an alternating periodic site potential V.
We employ both the zero-temperature density matrix renormalization group (DMRG)
method to determine the gap and critical behavior of the system and the
finite-temperature transfer matrix renormalization group method to evaluate the
thermodynamic properties. We find two critical points at U = and U =
that separate the BI and MI phases for a given V. A charge-neutral
spin-singlet exciton band develops in the BI phase (U<) and drops below
the band gap when U exceeds a special point Ue. The exciton gap closes at the
first critical point while the charge and spin gaps persist and coincide
between <U< where the system is dimerized. Both the charge and spin
gaps collapse at U = when the transition to the MI phase occurs. In the
MI phase (U>) the charge gap increases almost linearly with U while the
spin gap remains zero. These findings clarify earlier published results on the
same model, and offer insights into several important issues regarding an
appropriate scaling analysis of DMRG data and a full physical picture of the
delicate nature of the phase transitions driven by electron correlation. The
present work provides a comprehensive understanding for the critical behavior
and phase diagram for the transition from BI to MI in one-dimensional
correlated electron systems with a periodic alternating site potential.Comment: long version, 10 figure
Measurements of the observed cross sections for exclusive light hadrons containing at , 3.650 and 3.6648 GeV
By analyzing the data sets of 17.3, 6.5 and 1.0 pb taken,
respectively, at , 3.650 and 3.6648 GeV with the BES-II
detector at the BEPC collider, we measure the observed cross sections for
, , ,
and at the three energy
points. Based on these cross sections we set the upper limits on the observed
cross sections and the branching fractions for decay into these
final states at 90% C.L..Comment: 7 pages, 2 figure
Partial wave analysis of J/\psi \to \gamma \phi \phi
Using events collected in the BESII detector, the
radiative decay is
studied. The invariant mass distribution exhibits a near-threshold
enhancement that peaks around 2.24 GeV/.
A partial wave analysis shows that the structure is dominated by a
state () with a mass of
GeV/ and a width of GeV/. The
product branching fraction is: .Comment: 11 pages, 4 figures. corrected proof for journa
Direct Measurements of Absolute Branching Fractions for D0 and D+ Inclusive Semimuonic Decays
By analyzing about 33 data sample collected at and around 3.773
GeV with the BES-II detector at the BEPC collider, we directly measure the
branching fractions for the neutral and charged inclusive semimuonic decays
to be and , and determine the ratio of the two branching
fractions to be
Direct Measurements of the Branching Fractions for and and Determinations of the Form Factors and
The absolute branching fractions for the decays and
are determined using singly
tagged sample from the data collected around 3.773 GeV with the
BES-II detector at the BEPC. In the system recoiling against the singly tagged
meson, events for and events for decays are observed. Those yield
the absolute branching fractions to be and . The
vector form factors are determined to be
and . The ratio of the two form
factors is measured to be .Comment: 6 pages, 5 figure
Study of J/psi decays to Lambda Lambdabar and Sigma0 Sigma0bar
The branching ratios and Angular distributions for J/psi decays to Lambda
Lambdabar and Sigma0 Sigma0bar are measured using BESII 58 million J/psi.Comment: 11 pages, 5 figure
Measurements of J/psi Decays into 2(pi+pi-)eta and 3(pi+pi-)eta
Based on a sample of 5.8X 10^7 J/psi events taken with the BESII detector,
the branching fractions of J/psi--> 2(pi+pi-)eta and J/psi-->3(pi+pi-)eta are
measured for the first time to be (2.26+-0.08+-0.27)X10^{-3} and
(7.24+-0.96+-1.11)X10^{-4}, respectively.Comment: 11 pages, 6 figure
Carbon cycle uncertainty in the Alaskan Arctic
Climate change is leading to a disproportionately
large warming in the high northern latitudes, but the magnitude and sign of the future carbon balance of the Arctic are highly uncertain. Using 40 terrestrial biosphere models for the Alaskan Arctic from four recent model intercomparison projects – NACP (North American Carbon Program) site and regional syntheses, TRENDY (Trends in net land atmosphere carbon exchanges), and WETCHIMP (Wetland and Wetland CH4 Inter-comparison of Models Project) – we provide a baseline of terrestrial carbon cycle uncertainty, defined as the multi-model standard deviation (o) for each quantity that follows. Mean annual absolute uncertainty was largest for soil carbon (14.0±9.2 kgCm−2), then gross primary production (GPP) (0.22±0.50 kgCm−2 yr−1), ecosystem respiration (Re) (0.23±0.38 kgCm−2 yr−1), net primary production (NPP) (0.14±0.33 kgCm−2 yr−1), autotrophic respiration (Ra) (0.09±0.20 kgCm−2 yr−1), heterotrophic respiration (Rh) (0.14±0.20 kgCm−2 yr−1), net ecosystem exchange (NEE) (−0.01±0.19 kgCm−2 yr−1), and CH4 flux
(2.52±4.02 g CH4 m−2 yr−1). There were no consistent spatial
patterns in the larger Alaskan Arctic and boreal regional
carbon stocks and fluxes, with some models showing NEE
for Alaska as a strong carbon sink, others as a strong carbon source, while still others as carbon neutral. Finally, AmeriFlux data are used at two sites in the Alaskan Arctic to evaluate the regional patterns; observed seasonal NEE was captured within multi-model uncertainty. This assessment of carbon cycle uncertainties may be used as a baseline for the improvement of experimental and modeling activities, as well as a reference for future trajectories in carbon cycling with climate change in the Alaskan Arctic and larger boreal region
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