9,347 research outputs found
Selenium as a Catalyst in the Determination of Kitrogen in Cotton Seed Meal by the Kjeldahl Method
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
Nonlinear transverse cascade and sustenance of MRI-turbulence in Keplerian disks with an azimuthal magnetic field
We investigate magnetohydrodynamic turbulence driven by the magnetorotational
instability (MRI) in Keplerian disks with a nonzero net azimuthal magnetic
field using shearing box simulations. As distinct from most previous studies,
we analyze turbulence dynamics in Fourier (-) space to understand its
sustenance. The linear growth of MRI with azimuthal field has a transient
character and is anisotropic in Fourier space, leading to anisotropy of
nonlinear processes in Fourier space. As a result, the main nonlinear process
appears to be a new type of angular redistribution of modes in Fourier space --
the \emph{nonlinear transverse cascade} -- rather than usual direct/inverse
cascade. We demonstrate that the turbulence is sustained by interplay of the
linear transient growth of MRI (which is the only energy supply for the
turbulence) and the transverse cascade. These two processes operate at large
length scales, comparable to box size and the corresponding small wavenumber
area, called \emph{vital area} in Fourier space is crucial for the sustenance,
while outside the vital area direct cascade dominates. The interplay of the
linear and nonlinear processes in Fourier space is generally too intertwined
for a vivid schematization. Nevertheless, we reveal the \emph{basic subcycle}
of the sustenance that clearly shows synergy of these processes in the
self-organization of the magnetized flow system. This synergy is quite robust
and persists for the considered different aspect ratios of the simulation
boxes. The spectral characteristics of the dynamical processes in these boxes
are qualitatively similar, indicating the universality of the sustenance
mechanism of the MRI-turbulence.Comment: 32 pages, 17 figures, accepted for publication in Ap
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
A relativistically covariant version of Bohm's quantum field theory for the scalar field
We give a relativistically covariant, wave-functional formulation of Bohm's
quantum field theory for the scalar field based on a general foliation of
space-time by space-like hypersurfaces. The wave functional, which guides the
evolution of the field, is space-time-foliation independent but the field
itself is not. Hence, in order to have a theory in which the field may be
considered a beable, some extra rule must be given to determine the foliation.
We suggest one such rule based on the eigen vectors of the energy-momentum
tensor of the field itself.Comment: 1 figure. Submitted to J Phys A. 20/05/04 replacement has additional
references and a few minor changes made for clarity. Accepted by J Phys
Perspectives on partnership: Highlights of a literature review
Working in partnership has become central in efforts to address complex environmental, socio-economic, and technological problems. The terms partner or partnership appear more than 100 times in the Paris Declaration on Aid Effectiveness and more than 200 times in the version of the CGIAR's new Strategy and Results Framework presented at the recent Global Conference on Agricultural Research for Development. It is promoted as an effective means to mobilise the resources and capacities needed to generate knowledge, stimulate innovation and influence decision-making. Nevertheless, partnering is often experienced as timeconsuming and frustrating, and it has proved difficult to demonstrate its 'value added'. To improve partnering at the International Potato Center (CIP), we reviewed publications, evaluations and reports dealing with partnership. Rather than a single 'partnership literature' we found several different literatures that approach the subject from different perspectives. Several themes – relating to partnering processes vs. partnership structures, partnership dynamics, types of partnership, incentives for partnering, the key role of trust, power and equity issues, success factors and evaluation – cut across the distinct literatures. This ILAC Brief presents findings in each of these areas, notes some prominent knowledge gaps and identifies areas for future study
A non-local, Lorentz-invariant, hidden-variable interpretation of relativistic quantum mechanics based on particle trajectories
We demonstrate how to construct a lorentz-invariant, hidden-variable
interpretation of relativistic quantum mechanics based on particle
trajectories. The covariant theory that we propose employs a multi-time
formalism and a lorentz-invariant rule for the coordination of the space-time
points on the individual particle trajectories. In this way we show that there
is no contradiction between nonlocality and lorentz invariance in quantum
mechanics. The approach is illustrated for relativistic bosons, using a simple
model to discuss the individual non-locally correlated particle motion which
ensues when the wavefunction is entangled. A simple example of measurement is
described.Comment: 12 pages, 2 figure
Selenium as a Catalyst in the Determination of Kitrogen in Cotton Seed Meal by the Kjeldahl Method
Soil moisture and evapotranspiration predictions using Skylab data
The author has identified the following significant results. Multispectral reflectance and emittance data from the Skylab workshop were evaluated for prediction of evapotranspiration and soil moisture for an irrigated region of southern Texas. Wavelengths greater than 2.1 microns were required to spectrally distinguish between wet and dry fallow surfaces. Thermal data provided a better estimate of soil moisture than did data from the reflective bands. Thermal data were dependent on soil moisture but not on the type of agricultural land use. The emittance map, when used in conjunction with existing models, did provide an estimate of evapotranspiration rates. Surveys of areas of high soil moisture can be accomplished with space altitude thermal data. Thermal data will provide a reliable input into irrigation scheduling
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
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