1,422 research outputs found

    Effect of cultivation, tillage practice, and fertilization on total organic carbon, light fraction, and microbial biomass carbon in soils from the Loess Plateau of China and the Canadian prairies

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    Non-Peer ReviewedThree soils: Huangmian, Huihe, Heilu soil, from the Loess Plateau and one soil: Orthic Brown Chernozem, from the Canadian Prairies, were used to evaluate the effect of cultivation time, tillage system and fertilization, on total soil organic carbon (SOC), light fraction (LF), and microbial biomass carbon (MB-C). Upon cultivation, Huangmian soil lost 77% of total organic carbon within 5 years (0-20 cm), at a decrease rate of 2.15 tonnes C ha-1 yr-1. The Huihe soil lost 70% of total organic carbon at rate of 0.96-1.06 tonnes C ha-1 yr—1 over 42 years (0-20 cm). Comparably, the Orthic Brown Chernozem lost 11% and 44% of the total soil organic carbon mass (0-20 cm), after 40 and 80 years of cultivation respectively, at a corresponding rate of 0.17 tonnes C ha-1 yr-1 and 0.45 tonnes C ha-1 yr-1. Water erosion for the Huangmian and Huihe soil, and wind erosion for the Brown Chernozem during 1930’s, are the main reasons for organic carbon decline. The light fraction of organic carbon (LFOC) decreased more rapidly than total organic carbon: LFOC decreased by 73% and 90% for the Huangmian and Huihe soil for the corresponding period, and decreased by 70% and 74% for Brown Chernozem brought under cultivated 40 and 80 years ago respectively. The change of microbial biomass carbon (MB-C) showed same trend as total organic carbon and LFOC. On the Heilu soil, a 29% decrease of SOC, which was comparable to average 22% decline of SOC during about hundred years of cultivation on the Prairie, was observed after thousands of years of cultivation relative to native sod. Some management practices had a positive effect on restoring and maintaining soil organic carbon. On the Orthic Brown Chernozem, dry matter of light fraction in 0-5 cm was increased after no-tillage was practiced for 7 years. As well, LFOC in 0-5 cm was increased significantly after switching from cereal-fallow to continuous cropping for 10 years. Growing alfalfa for 10 years after 60 years cereal-fallow increased total organic carbon by 80% and 27% in 0-5 cm and 5-10 cm depths respectively, while dry matter of LF and LFOC were increased by 54% and 194%, and 245% and 286% in 0-5 cm and 5-10 cm respectively. Application of manure alone and manure plus chemical fertilizer was found to restore total organic carbon, LFOC, and MB-C in the Heilu soil

    Crystallization of diamond-like carbon to graphene under low energy ion beam modification

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    Low-energy ion beam modification was proposed to create graphene on the top of the insulated diamond-like carbon films. In such low-temperature fabrication process the surface of the amorphous carbon could crystallize to graphene as a result of point defect creation and enhanced diffusion caused by the ion bombardment. In the experiment 130 eV argon ion irradiation was used. After the modification the resistivity of the sample surface drops. Raman spectra of the samples measured at 633 nm showed partial crystallization and were similar to the spectra of defected graphene. This result is very encouraging and we hope that by improving this technology it will be possible to fabricate defect-free graphene, which can be used in electronics without transfer to other substrate

    Knotlike Cosmic Strings in The Early Universe

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    In this paper, the knotlike cosmic strings in the Riemann-Cartan space-time of the early universe are discussed. It has been revealed that the cosmic strings can just originate from the zero points of the complex scalar quintessence field. In these strings we mainly study the knotlike configurations. Based on the integral of Chern-Simons 3-form a topological invariant for knotlike cosmic strings is constructed, and it is shown that this invariant is just the total sum of all the self-linking and linking numbers of the knots family. Furthermore, it is also pointed out that this invariant is preserved in the branch processes during the evolution of cosmic strings

    Theoretical study of the two-proton halo candidate 17^{17}Ne including contributions from resonant continuum and pairing correlations

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    With the relativistic Coulomb wave function boundary condition, the energies, widths and wave functions of the single proton resonant orbitals for 17^{17}Ne are studied by the analytical continuation of the coupling constant (ACCC) approach within the framework of the relativistic mean field (RMF) theory. Pairing correlations and contributions from the single-particle resonant orbitals in the continuum are taken into consideration by the resonant Bardeen-Cooper-Schrieffer (BCS) approach, in which constant pairing strength is used. It can be seen that the fully self-consistent calculations with NL3 and NLSH effective interactions mostly agree with the latest experimental measurements, such as binding energies, matter radii, charge radii and densities. The energy of π\pi2s1/2_{1/2} orbital is slightly higher than that of π1d5/2\pi1d_{5/2} orbital, and the occupation probability of the (π(\pi2s1/2)2_{1/2})^2 orbital is about 20%, which are in accordance with the shell model calculation and three-body model estimation

    Critical depinning force and vortex lattice order in disordered superconductors

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    We simulate the ordering of vortices and its effects on the critical current in superconductors with varied vortex-vortex interaction strength and varied pinning strengths for a two-dimensional system. For strong pinning the vortex lattice is always disordered and the critical depinning force only weakly increases with decreasing vortex-vortex interactions. For weak pinning the vortex lattice is defect free until the vortex-vortex interactions have been reduced to a low value, when defects begin to appear with a simultaneous rapid increase in the critical depinning force. In each case the depinning force shows a maximum for non-interacting vortices. The relative height of the peak increases and the peak width decreases for decreasing pinning strength in excellent agreement with experimental trends associated with the peak effect. We show that scaling relations exist between the distance between defects in the vortex lattice and the critical depinning force.Comment: 5 pages, 6 figure

    Studying Precipitation Processes in WRF with Goddard Bulk Microphysics in Comparison with Other Microphysical Schemes

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    A Goddard bulk microphysical parameterization is implemented into the Weather Research and Forecasting (WRF) model. This bulk microphysical scheme has three different options, 2ICE (cloud ice & snow), 3ICE-graupel (cloud ice, snow & graupel) and 3ICE-hail (cloud ice, snow & hail). High-resolution model simulations are conducted to examine the impact of microphysical schemes on different weather events: a midlatitude linear convective system and an Atlantic hurricane. The results suggest that microphysics has a major impact on the organization and precipitation processes associated with a summer midlatitude convective line system. The Goddard 3ICE scheme with the cloud ice-snow-hail configuration agreed better with observations ill of rainfall intensity and having a narrow convective line than did simulations with the cloud ice-snow-graupel and cloud ice-snow (i.e., 2ICE) configurations. This is because the Goddard 3ICE-hail configuration has denser precipitating ice particles (hail) with very fast fall speeds (over 10 m/s) For an Atlantic hurricane case, the Goddard microphysical scheme (with 3ICE-hail, 3ICE-graupel and 2ICE configurations) had no significant impact on the track forecast but did affect the intensity slightly. The Goddard scheme is also compared with WRF's three other 3ICE bulk microphysical schemes: WSM6, Purdue-Lin and Thompson. For the summer midlatitude convective line system, all of the schemes resulted in simulated precipitation events that were elongated in southwest-northeast direction in qualitative agreement with the observed feature. However, the Goddard 3ICE-hail and Thompson schemes were closest to the observed rainfall intensities although the Goddard scheme simulated more heavy rainfall (over 48 mm/h). For the Atlantic hurricane case, none of the schemes had a significant impact on the track forecast; however, the simulated intensity using the Purdue-Lin scheme was much stronger than the other schemes. The vertical distributions of model-simulated cloud species (e.g., snow) are quite sensitive to the microphysical schemes, which is an issue for future verification against satellite retrievals. Both the Purdue-Lin and WSM6 schemes simulated very little snow compared to the other schemes for both the midlatitude convective line and hurricane case. Sensitivity tests with these two schemes showed that increasing the snow intercept, turning off the auto-conversion from snow to graupel, eliminating dry growth, and reducing the transfer processes from cloud-sized particles to precipitation-sized ice collectively resulted in a net increase in those schemes' snow amounts

    Metastability and Transient Effects in Vortex Matter Near a Decoupling Transition

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    We examine metastable and transient effects both above and below the first-order decoupling line in a 3D simulation of magnetically interacting pancake vortices. We observe pronounced transient and history effects as well as supercooling and superheating between the 3D coupled, ordered and 2D decoupled, disordered phases. In the disordered supercooled state as a function of DC driving, reordering occurs through the formation of growing moving channels of the ordered phase. No channels form in the superheated region; instead the ordered state is homogeneously destroyed. When a sequence of current pulses is applied we observe memory effects. We find a ramp rate dependence of the V(I) curves on both sides of the decoupling transition. The critical current that we obtain depends on how the system is prepared.Comment: 10 pages, 15 postscript figures, version to appear in PR

    History effects and pinning regimes in solid vortex matter

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    We propose a phenomenological model that accounts for the history effects observed in ac susceptibility measurements in YBa2Cu3O7 single crystals [Phys. Rev. Lett. 84, 4200 (2000) and Phys. Rev. Lett. 86, 504 (2001)]. Central to the model is the assumption that the penetrating ac magnetic field modifies the vortex lattice mobility, trapping different robust dynamical states in different regions of the sample. We discuss in detail on the response of the superconductor to an ac magnetic field when the vortex lattice mobility is not uniform inside the sample. We begin with an analytical description for a simple geometry (slab) and then we perform numerical calculations for a strip in a transverse magnetic field which include relaxation effects. In calculations, the vortex system is assumed to coexist in different pinning regimes. The vortex behavior in the regions where the induced current density j has been always below a given threshold (j_c^>) is described by an elastic Campbell-like regime (or a critical state regime with local high critical current density, j_c^>). When the VS is shaken by symmetrical (e.g. sinusoidal) ac fields, the critical current density is modified to j_c^) at regions where vortices have been forced to oscillate by a current density larger than j_c^>. Experimentally, an initial state with high critical current density (j_c^>) can be obtained by zero field cooling, field cooling (with no applied ac field) or by shaking the vortex lattice with an asymmetrical (e.g. sawtooth) field. We compare our calculations with experimental ac susceptibility results in YBa2Cu3O7 single crystals.Comment: 11 pages, 7 figures. To be published in PR

    Disordered Type-II Superconductors: A Universal Phase Diagram for Low-Tc_c Systems

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    A universal phase diagram for weakly pinned low-Tc_c type-II superconductors is revisited and extended with new proposals. The low-temperature ``Bragg glass'' phase is argued to transform first into a disordered, glassy phase upon heating. This glassy phase, a continuation of the high-field equilibrium vortex glass phase, then melts at higher temperatures into a liquid. This proposal provides an explanation for the anomalies observed in the peak effect regime of 2H-NbSe2_2 and several other low-Tc_c materials which is independent of the microscopic mechanisms of superconductivity in these systems.Comment: 23 pages, 9 figure

    Peak effect in a superconducting DyBa2Cu3O7-y film at microwave frequencies

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    We report the observation of a peak in the microwave (9.55 GHz) surface resistance in an epitaxial DyBa2Cu3O7-y superconducting film in magnetic fields (parallel to the c axis) ranging between 0.2 to 0.9 Tesla. Such a peak is absent in the measurements done in zero-field. The temperature and field dependence of the peak suggests that this peak could be associated with the peak effect phenomenon reflecting the order-disorder transformation in the flux-line lattice. A strong dependence of this peak effect at frequencies close to the depinning frequency of the flux line lattice is observed.Comment: 1 text, 4 figures (all postscript) to be published in Phys. Rev.
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