15,653 research outputs found
Increase in soil organic carbon by agricultural intensification in northern China
Acknowledgements. This research was supported by National Natural Science Foundation of China (no. 31370527 and 31261140367) and the National Science and Technology Support Program of China (no. 2012BAD14B01-2). The authors gratefully thank the Huantai Agricultural Station for providing of the Soil Fertility Survey data. We also thank Zheng Liang from China Agricultural University for the soil sampling and analysis in 2011. Thanks are extended to Jessica Bellarby for helpful discussion and suggestions.Peer reviewedPublisher PD
On the Nature of X(4260)
We study the property of resonance by re-analyzing all experimental
data available, especially the cross section data. The final state
interactions of the , couple channel system are also taken
into account. A sizable coupling between the and is
found. The inclusion of the data indicates a small value of
eV.Comment: Refined analysis with new experimental data included. 13 page
Magnetic rotations in 198Pb and 199Pb within covariant density functional theory
Well-known examples of shears bands in the nuclei 198Pb and 199Pb are
investigated within tilted axis cranking relativistic mean-field theory. Energy
spectra, the relation between spin and rotational frequency, deformation
parameters and reduced and transition probabilities are calculated.
The results are in good agreement with available data and with calculations
based on the phenomenological pairing plus-quadrupole-quadrupole tilted-axis
cranking model. It is shown that covariant density functional theory provides a
successful microscopic and fully self-consistent description of magnetic
rotation in the Pb region showing the characteristic properties as the shears
mechanism and relatively large B(M1) transitions decreasing with increasing
spin.Comment: 22 pages, 8 figure
Conduction mechanisms of epitaxial EuTiO3 thin films
To investigate leakage current density versus electric field characteristics,
epitaxial EuTiO3 thin films were deposited on (001) SrTiO3 substrates by pulsed
laser deposition and were post-annealed in a reducing atmosphere. This
investigation found that conduction mechanisms are strongly related to
temperature and voltage polarity. It was determined that from 50 to 150 K the
dominant conduction mechanism was a space-charge-limited current under both
negative and positive biases. From 200 to 300 K, the conduction mechanism shows
Schottky emission and Fowler-Nordheim tunneling behaviors for the negative and
positive biases, respectively. This work demonstrates that Eu3+ is one source
of leakage current in EuTiO3 thin films.Comment: 17 pages,4 figures, conferenc
An MHD Model For Magnetar Giant Flares
Giant flares on soft gamma-ray repeaters that are thought to take place on
magnetars release enormous energy in a short time interval. Their power can be
explained by catastrophic instabilities occurring in the magnetic field
configuration and the subsequent magnetic reconnection. By analogy with the
coronal mass ejection (CME) events on the Sun, we develop a theoretical model
via an analytic approach for magnetar giant flares. In this model, the rotation
and/or displacement of the crust causes the field to twist and deform, leading
to flux rope formation in the magnetosphere and energy accumulation in the
related configuration. When the energy and helicity stored in the configuration
reach a threshold, the system loses its equilibrium, the flux rope is ejected
outward in a catastrophic way, and magnetic reconnection helps the catastrophe
develop to a plausible eruption. By taking SGR 1806 - 20 as an example, we
calculate the free magnetic energy released in such an eruptive process and
find that it is more than ergs, which is enough to power a giant
flare. The released free magnetic energy is converted into radiative energy,
kinetic energy and gravitational energy of the flux rope. We calculated the
light curves of the eruptive processes for the giant flares of SGR 1806 - 20,
SGR 0526-66 and SGR 1900+14, and compared them with the observational data. The
calculated light curves are in good agreement with the observed light curves of
giant flares.Comment: Accepted to Ap
Structure, morphology, and mechanical properties of polysiloxane elastomer composites prepared by in situ polymerization of zinc dimethacrylate
Methyl vinyl silicone rubber/zinc dimethacrylate (VMQ/ZDMA) composites were prepared through in situ polymerization of ZDMA monomers during the peroxide curing. The polymerization conversion of ZDMA and morphology of the VMQ/ZDMA composites were studied. The results showed that most of the ZDMA monomers participated in the in situ polymerization during the cross-linking of the VMQ matrix and uniform nanophases were formed in the composites. The ‘dissolving-diffusion’ model was used to explain the micro-nano transformation of ZDMA. According to the model, a uniform nano-dispersed structure could be obtained through the in situ reaction even though the initial dispersion of ZDMA in the blends was poor. In addition, tensile tests of VMQ/ZDMA composites showed that ZDMA had a significant reinforcement on the mechanical properties of VMQ, and the best mechanical properties were obtained when the amounts of peroxide and ZDMA were 5 and 40 phr, respectively. The gross crosslink density and ionic crosslink density increased as the amount of ZDMA increased, but the covalent crosslink density decreased slightly. These results indicated that the ionic crosslink structure had a significant effect on the mechanical properties of VMQ/ZDMA composites
Pressure dependence of the superconducting transition and electron correlations in Na_xCoO_2 \cdot 1.3H_2O
We report T_c and ^{59}Co nuclear quadrupole resonance (NQR) measurements on
the cobalt oxide superconductor Na_{x}CoO_{2}\cdot 1.3H_{2}O (T_c=4.8 K) under
hydrostatic pressure (P) up to 2.36 GPa. T_c decreases with increasing pressure
at an average rate of -0.49\pm0.09 K/GPa. At low pressures P\leq0.49 GPa, the
decrease of T_c is accompanied by a weakening of the spin correlations at a
finite wave vector and a reduction of the density of states (DOS) at the Fermi
level. At high pressures above 1.93 GPa, however, the decrease of T_c is mainly
due to a reduction of the DOS. These results indicate that the
electronic/magnetic state of Co is primarily responsible for the
superconductivity. The spin-lattice relaxation rate 1/T_1 at P=0.49 GPa shows a
T^3 variation below T_c down to T\sim 0.12T_c, which provides compelling
evidence for the presence of line nodes in the superconducting gap function.Comment: published on 19, Sept. 2007 on Phys. Rev.
Composite Polarons in Ferromagnetic Narrow-band Metallic Manganese Oxides
A new mechanism is proposed to explain the colossal magnetoresistance and
related phenomena. Moving electrons accompanied by Jahn-Teller phonon and
spin-wave clouds may form composite polarons in ferromagnetic narrow-band
manganites. The ground-state and finite-temperature properties of such
composite polarons are studied in the present paper. By using a variational
method, it is shown that the energy of the system at zero temperature decreases
with the formation of composite polaron; the energy spectrum and effective mass
of the composite polaron at finite temperature is found to be strongly
renormalized by the temperature and the magnetic field. It is suggested that
the composite polaron contribute significantly to the transport and the
thermodynamic properties in ferromagnetic narrow-band metallic manganese
oxides.Comment: Latex, no figur
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