3,786 research outputs found
Modeling the effect of soil meso- and macropores topology on the biodegradation of a soluble carbon substrate
Soil structure and interactions between biotic and abiotic processes are increasingly recognized as important for explaining the large uncertainties in the outputs of macroscopic SOM decomposition models. We present a numerical analysis to assess the role of meso- and macropore topology on the biodegradation of a soluble carbon substrate in variably water saturated and pure diffusion conditions . Our analysis was built as a complete factorial design and used a new 3D pore-scale model, LBioS, that couples a diffusion Lattice-Boltzmann model and a compartmental biodegradation model. The scenarios combined contrasted modalities of four factors: meso- and macropore space geometry, water saturation, bacterial distribution and physiology. A global sensitivity analysis of these factors highlighted the role of physical factors in the biodegradation kinetics of our scenarios. Bacteria location explained 28% of the total variance in substrate concentration in all scenarios, while the interactions among location, saturation and geometry explained up to 51% of it
Time-dependent q-deformed coherent states for generalized uncertainty relations
We investigate properties of generalized time-dependent q-deformed coherent states for a noncommutative harmonic oscillator. The states are shown to satisfy a generalized version of Heisenberg's uncertainty relations. For the initial value in time the states are demonstrated to be squeezed, i.e. the inequalities are saturated, whereas when time evolves the uncertainty product oscillates away from this value albeit still respecting the relations. For the canonical variables on a noncommutative space we verify explicitly that Ehrenfest's theorem hold at all times. We conjecture that the model exhibits revival times to infinite order. Explicit sample computations for the fractional revival times and superrevival times are presented
Inertial terms to magnetization dynamics in ferromagnetic thin films
Inertial magnetization dynamics have been predicted at ultrahigh speeds, or
frequencies approaching the energy relaxation scale of electrons, in
ferromagnetic metals. Here we identify inertial terms to magnetization dynamics
in thin NiFe and Co films near room temperature. Effective
magnetic fields measured in high-frequency ferromagnetic resonance (115-345
GHz) show an additional stiffening term which is quadratic in frequency and
80 mT at the high frequency limit of our experiment. Our results extend
understanding of magnetization dynamics at sub-picosecond time scales.Comment: 11 pages, 3 figure
Homogenization of linear transport equations in a stationary ergodic setting
We study the homogenization of a linear kinetic equation which models the
evolution of the density of charged particles submitted to a highly oscillating
electric field. The electric field and the initial density are assumed to be
random and stationary. We identify the asymptotic microscopic and macroscopic
profiles of the density, and we derive formulas for these profiles when the
space dimension is equal to one.Comment: 24 page
Productivity and Subsidies in European Union Countries: An Analysis for Dairy Farms Using Input Distance Frontiers
The major objective of this paper is to examine the association between agricultural subsidies and farm efficiency using data from the European Farm Accountancy Data Network (FADN) for operations specializing on dairy. The analysis covers the 18 year period going from 1990 to 2007 and includes the following seven countries: Denmark; France; Germany; Ireland; Spain; the Netherlands; and the United Kingdom. Separate translog stochastic input distance frontiers are estimated for each country. The key results show high average technical efficiency (TE) ranging from 91.8% to 94.9%, average rates of technological change going from -0.6% to 1.4%, and increasing returns to scale (1.24 to 1.44) across all seven countries. In addition, higher subsidy and hired labor dependence are found to be significantly associated with higher technical inefficiency across all seven countries. Moreover, the latest Common Agricultural Policy (CAP) regime introducing fully decoupled payments has reduced TE in all countries considered except Denmark.Subsidies, CAP, technical efficiency, technological progress, returns to scale, Europe, dairy production, input distance frontiers, Livestock Production/Industries, Productivity Analysis,
Numerical Simulations of Dynamos Generated in Spherical Couette Flows
We numerically investigate the efficiency of a spherical Couette flow at
generating a self-sustained magnetic field. No dynamo action occurs for
axisymmetric flow while we always found a dynamo when non-axisymmetric
hydrodynamical instabilities are excited. Without rotation of the outer sphere,
typical critical magnetic Reynolds numbers are of the order of a few
thousands. They increase as the mechanical forcing imposed by the inner core on
the flow increases (Reynolds number ). Namely, no dynamo is found if the
magnetic Prandtl number is less than a critical value .
Oscillating quadrupolar dynamos are present in the vicinity of the dynamo
onset. Saturated magnetic fields obtained in supercritical regimes (either
or ) correspond to the equipartition between magnetic and
kinetic energies. A global rotation of the system (Ekman numbers ) yields to a slight decrease (factor 2) of the critical magnetic
Prandtl number, but we find a peculiar regime where dynamo action may be
obtained for relatively low magnetic Reynolds numbers (). In this
dynamical regime (Rossby number , spheres in opposite direction) at
a moderate Ekman number (), a enhanced shear layer around the inner
core might explain the decrease of the dynamo threshold. For lower
() this internal shear layer becomes unstable, leading to small
scales fluctuations, and the favorable dynamo regime is lost. We also model the
effect of ferromagnetic boundary conditions. Their presence have only a small
impact on the dynamo onset but clearly enhance the saturated magnetic field in
the ferromagnetic parts. Implications for experimental studies are discussed
Signatures of Secondary Collisionless Magnetic Reconnection Driven by Kink Instability of a Flux Rope
The kinetic features of secondary magnetic reconnection in a single flux rope
undergoing internal kink instability are studied by means of three-dimensional
Particle-in-Cell simulations. Several signatures of secondary magnetic
reconnection are identified in the plane perpendicular to the flux rope: a
quadrupolar electron and ion density structure and a bipolar Hall magnetic
field develop in proximity of the reconnection region. The most intense
electric fields form perpendicularly to the local magnetic field, and a
reconnection electric field is identified in the plane perpendicular to the
flux rope. An electron current develops along the reconnection line in the
opposite direction of the electron current supporting the flux rope magnetic
field structure. Along the reconnection line, several bipolar structures of the
electric field parallel to the magnetic field occur making the magnetic
reconnection region turbulent. The reported signatures of secondary magnetic
reconnection can help to localize magnetic reconnection events in space,
astrophysical and fusion plasmas
Lipid And Oxylipin Profiles During Aging And Sprout Development In Potato Tubers (Solanum Tuberosum L.)
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