8,166 research outputs found
Approximate perturbed direct homotopy reduction method: infinite series reductions to two perturbed mKdV equations
An approximate perturbed direct homotopy reduction method is proposed and
applied to two perturbed modified Korteweg-de Vries (mKdV) equations with
fourth order dispersion and second order dissipation. The similarity reduction
equations are derived to arbitrary orders. The method is valid not only for
single soliton solution but also for the Painlev\'e II waves and periodic waves
expressed by Jacobi elliptic functions for both fourth order dispersion and
second order dissipation. The method is valid also for strong perturbations.Comment: 8 pages, 1 figur
Magnetic structure of superconducting Eu(Fe0.82Co0.18)2As2 as revealed by single-crystal neutron diffraction
The magnetic structure of superconducting Eu(Fe0.82Co0.18)2As2 is
unambiguously determined by single-crystal neutron diffraction. A long-range
ferromagnetic order of the Eu2+ moments along the c-direction is revealed below
the magnetic phase transition temperature Tc = 17 K. In addition, the
antiferromagnetism of the Fe2+ moments still survives and the
tetragonal-to-orthorhombic structural phase transition is also observed,
although the transition temperatures of the Fe-spin density wave (SDW) order
and the structural phase transition are significantly suppressed to Tn = 70 K
and Ts = 90 K, respectively, compared to the parent compound EuFe2As2.We
present the microscopic evidences for the coexistence of the Eu-ferromagnetism
(FM) and the Fe-SDW in the superconducting crystal. The superconductivity (SC)
competes with the Fe-SDW in Eu(Fe0.82Co0.18)2As2.Moreover, the comparison
between Eu(Fe1-xCox)2As2 and Ba(Fe1-xCox)2As2 indicates a considerable
influence of the rare-earth element Eu on the magnetism of the Fe sublattice.Comment: 7 pages, 7 figures, accepted for publication in Physical Review
Upper critical field and thermally activated flux flow in single crystalline TlRbFeSe
The upper critical field of
TlRbFeSe single crystals has been determined by
means of measuring the electrical resistivity in both a pulsed magnetic field
(60T) and a DC magnetic field (14T). It is found that
linearly increases with decreasing temperature for ,
reaching T. On the
other hand, a larger with a strong convex curvature
is observed for ((18K)60T). This compound shows a moderate anisotropy of the upper
critical field around , but decreases with decreasing temperature.
Analysis of the upper critical field based on the Werthamer-Helfand-Hohenberg
(WHH) method indicates that is orbitally limited for
, but the effect of spin paramagnetism may play an
important role on the pair breaking for . All these
experimental observations remarkably resemble those of the iron pnictide
superconductors, suggesting a unified scenario for the iron-based
superconductors. Moreover, the superconducting transition is significantly
broadened upon applying a magnetic field, indicating strong thermal fluctuation
effects in the superconducting state of
TlRbFeSe. The derived thermal activation energy
for vortex motion is compatible with those of the 1111-type iron pnictides.Comment: 7 pages, 6 figure
Lytic viral infection of bacterioplankton in deep waters of the western Pacific Ocean
As the most abundant biological entities in the ocean, viruses influence host
mortality and nutrient recycling mainly through lytic infection. Yet, the
ecological characteristics of virioplankton and viral impacts on host
mortality and biogeochemical cycling in the deep sea are largely unknown. In
the present study, viral abundance and lytic infection were investigated
throughout the water column in the western Pacific Ocean. Both the
prokaryotic and viral abundance and production showed a significantly
decreasing trend from epipelagic to meso- and bathypelagic waters. Viral
abundance decreased from 0.36–1.05 × 10<sup>10</sup> particles L<sup>−1</sup>
to 0.43–0.80 × 10<sup>9</sup> particles L<sup>−1</sup>, while the
virus : prokaryote ratio varied from 7.21 to
16.23 to 2.45–23.40, at the surface and 2000 m, respectively. Lytic viral
production rates in surface and 2000 m waters were, on average,
1.03 × 10<sup>10</sup> L<sup>−1</sup> day<sup>−1</sup> and
5.74 × 10<sup>8</sup> L<sup>−1</sup> day<sup>−1</sup>. Relatively high percentages of
prokaryotic cells lysed by viruses at 1000 and 2000 m were observed,
suggesting a significant contribution of viruses to prokaryotic mortality in
the deep ocean. The carbon released by viral lysis in deep western Pacific
Ocean waters was from 0.03 to 2.32 μg C L<sup>−1</sup> day<sup>−1</sup>. Our
findings demonstrated a highly dynamic and active viral population in these
deep waters and suggested that virioplankton play an important role in the
microbial loop and subsequently biogeochemical cycling in deep oceans
Oxidation and mechanical properties of in situ hybrid (TiCp+TiBw)/Ti6Al4V composites with tailored network microstructure
Ocean Acidification Regulates the Activity, Community Structure, and Functional Potential of Heterotrophic Bacterioplankton in an Oligotrophic Gyre
Ocean acidification (OA), a consequence of increased global carbon dioxide (CO2) emissions, is considered a major threat to marine ecosystems. Its effects on bacterioplankton activity, diversity, and community composition have received considerable attention. However, the direct impact of OA on heterotrophic bacterioplankton is often masked by the significant response of phytoplankton due to the close coupling of heterotrophic bacterioplankton and autotrophs. Here we investigated the responses of a heterotrophic bacterioplankton assemblage to high pCO2 (790-ppm) treatment in warm tropical western Pacific waters by conducting a microcosm experiment in dark for 12 days. Heterotrophic bacterioplankton abundance and production were enhanced by OA over the first 6 days of incubation, while the diversity and species richness were negatively affected. Bacterioplankton community composition in the high pCO2 treatment changed faster than that in the control. The molecular ecological network analysis showed that the elevated CO2 changed the overall connections among the bacterial community and resulted in a simple network under high CO2 condition. Species-specific responses to OA were observed and could be attributed to the different life strategies and to the ability of a given species to adapt to environmental conditions. In addition, high-throughput functional gene array analysis revealed that genes related to carbon and nitrogen cycling were positively affected by acidification. Together, our findings suggest that OA has direct effects on heterotrophic bacterioplankton in a low-latitude warm ocean and may therefore affect global biogeochemical cycles
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