9,291 research outputs found
Nonlinear transverse cascade and two-dimensional magnetohydrodynamic subcritical turbulence in plane shear flows
We find and investigate via numerical simulations self-sustained
two-dimensional turbulence in a magnetohydrodynamic flow with a maximally
simple configuration: plane, noninflectional (with a constant shear of
velocity) and threaded by a parallel uniform background magnetic field. This
flow is spectrally stable, so the turbulence is subcritical by nature and hence
it can be energetically supported just by transient growth mechanism due to
shear flow nonnormality. This mechanism appears to be essentially anisotropic
in spectral (wavenumber) plane and operates mainly for spatial Fourier
harmonics with streamwise wavenumbers less than a ratio of flow shear to the
Alfv\'{e}n speed, (i.e., the Alfv\'{e}n frequency is lower than
the shear rate). We focused on the analysis of the character of nonlinear
processes and underlying self-sustaining scheme of the turbulence, i.e., on the
interplay between linear transient growth and nonlinear processes, in spectral
plane. Our study, being concerned with a new type of the energy-injecting
process for turbulence -- the transient growth, represents an alternative to
the main trends of MHD turbulence research. We find similarity of the nonlinear
dynamics to the related dynamics in hydrodynamic flows -- to the \emph{bypass}
concept of subcritical turbulence. The essence of the analyzed nonlinear MHD
processes appears to be a transverse redistribution of kinetic and magnetic
spectral energies in wavenumber plane [as occurs in the related hydrodynamic
flow, see Horton et al., Phys. Rev. E {\bf 81}, 066304 (2010)] and differs
fundamentally from the existing concepts of (anisotropic direct and inverse)
cascade processes in MHD shear flows.Comment: 19 pages, 7 figures, published in Phys. Rev. E 89, 043101 (2014
Measurement of neutrino oscillation with KamLAND: Evidence of spectral distortion
We present results of a study of neutrino oscillation based on a 766 ton/year exposure of KamLAND to reactor antineutrinos. We observe 258 v_e candidate events with energies above 3.4 MeV compared to 365.2±23.7 events expected in the absence of neutrino oscillation. Accounting for 17.8±7.3 expected background events, the statistical significance for reactor v_e over bar (e) disappearance is 99.998%. The observed energy spectrum disagrees with the expected spectral shape in the absence of neutrino oscillation at 99.6% significance and prefers the distortion expected from v_e oscillation effects. A two-neutrino oscillation analysis of the KamLAND data gives Δm^2=7.9_(-0.5)^(+0.6)x10^(-5) eV^2. A global analysis of data from KamLAND and solar-neutrino experiments yields
Δm^2=7.9_(-0.5)^(+0.6)x10^(-5) eV^2 and tan^2θ=0.40_(-0.07)^(+0.10), the most precise determination to date
High Sensitivity Search for v_e’s from the Sun and Other Sources at KamLAND
Data corresponding to a KamLAND detector exposure of 0.28 kton yr has been used to search for ν̅ _e’s in the energy range 8.3 < E_(ν̅e) < 14.8  MeV. No candidates were found for an expected background of 1.1±0.4 events. This result can be used to obtain a limit on ν̅_e fluxes of any origin. Assuming that all ν̅_e flux has its origin in the Sun and has the characteristic ^8B solar ν_e energy spectrum, we obtain an upper limit of 3.7×10^2  cm^(-2) ^(s-1) (90% C.L.) on the ν̅_e flux. We interpret this limit, corresponding to 2.8×10^(-4) of the standard solar model ^8B ν_e flux, in the framework of spin-flavor precession and neutrino decay models
Soil Water Infiltration as Affected by the Use of the Paraplow
DOUBLE-RING infiltration measurements were made during the corn growing season to determine the effect of various tillage systems on 1- and 30-min cumulative infiltration at three locations in Iowa. The Paraplow*, a newly introduced tillage tool in North America, which loosens the soil but does not invert it, was compared with moldboard-plow, chisel-plow, and no-tillage treatments. The Paraplow treatment gave the highest 1- and 30-min cumulative infiltration throughout the growing season. Similar bulk densities to a depth of 10 cm were observed for all the tillage treatments except for immediately after fall tillage at one site where moldboard-plowed and chisel-plowed soils had the lowest bulk densities. No-tillage and Paraplow treatment plots generally had greater moisture contents in the top 10 cm. Deep, surface connected cracks enhanced soil water infiltration considerably, and residue cover, particularly on the surface of no-tillage and Paraplow treatment plots, seemed to prevent surface sealing that would restrict soil water infiltration
Testing a nitrogen fertilizer applicator designed to reduce leaching losses
Conventional practices for nitrogen fertilization of corn produce soil conditions that are conducive to preferential water flow and nitrate leaching. A new fertilizer applicator is proposed that will more effectively protect the fertilizer from infiltrating water and thus reduce the potential for leaching. The device forms a small compacted layer of soil above the subsurface fertilizer band and then mounds soil into a surface dome directly above the fertilizer band. This new localized compaction and doming (LCD) method is evaluated by measuring soil physical properties around the fertilizer band and comparing them with measurements made within the conventional knifing system. The LCD applicator increased penetration resistance from 0.50 to 0.75 MPa at the fertilizer band. As the knife slit above the fertilizer band was closed by the LCD applicator, soil bulk density was increased from 1.2 to 1.4 g/cm3 in the region. The ponded infiltration rate through the fertilizer band was reduced from 19.7 cm/h at the conventional knife slit to 10.1 cm/h at the LCD surface. Reduced water flow through the fertilizer band will result in reduced NO3-N movement. Nitrate movement was measured during a growing season in a corn field, and NO3-N applied by the LCD applicator moved approximately 60% as deep as NO3-N applied by a conventional knife applicator. The ability to restrict NO3-N movement by modifying the surface soil at N application represents a simple yet effective strategy to reduce NO3-N leaching losses and possible impacts on groundwater quality
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