588 research outputs found
Ensiling of Different Legumes Compared to Grass
The objective of this study was to examine the ensiling characteristics of four different forage legumes: galega (Galega orientalis), lucerne (Medicago sativa), white clover (Trifolium repens) and red clover (Trifolium pratense), and compare these with perennial ryegrass (Lolium perenne), using different additives. The crops were mowed using a sickle bar mower and chopped using a precision chop harvester. The crops were ensiled either direct cut or wilted to 35-45% DM. Wilting took place on a barn drier. Forages were ensiled either untreated or with addition of formic acid, Promyr or Ecosyl. The silos were stored for 100 days before opening. Silages were generally well fermented, but application of Promyr or formic acid lowered the ammonia content of the silages
Weak localization effects in granular metals
The weak localization correction to the conductivity of a granular metal is
calculated using the diagrammatic technique in the reciprocal grain lattice
representation. The properties of this correction are very similar to that one
in disordered metal, with the replacement of the electron mean free path by the grain diameter and the dimensionless conductance by the
tunnelling dimensionless conductance . In particular, we demonstrate
that at zero temperature no conducting phase can exist for dimensions . We also analyze the WL correction to magnetoconductivity in the weak field
limit.Comment: 4 pages, 3 figures; minor corrections adde
Localization of Matter Waves in 2D-Disordered Optical Potentials
We consider ultracold atoms in 2D-disordered optical potentials and calculate
microscopic quantities characterizing matter wave quantum transport in the
non-interacting regime. We derive the diffusion constant as function of all
relevant microscopic parameters and show that coherent multiple scattering
induces significant weak localization effects. In particular, we find that even
the strong localization regime is accessible with current experimental
techniques and calculate the corresponding localization length.Comment: 4 pages, 3 figures, figures changed, references update
A renormalization group approach to time dependent transport through correlated quantum dots
We introduce a real time version of the functional renormalization group
which allows to study correlation effects on nonequilibrium transport through
quantum dots. Our method is equally capable to address (i) the relaxation out
of a nonequilibrium initial state into a (potentially) steady state driven by a
bias voltage and (ii) the dynamics governed by an explicitly time-dependent
Hamiltonian. All time regimes from transient to asymptotic can be tackled; the
only approximation is the consistent truncation of the flow equations at a
given order. As an application we investigate the relaxation dynamics of the
interacting resonant level model which describes a fermionic quantum dot
dominated by charge fluctuations. Moreover, we study decoherence and relaxation
phenomena within the ohmic spin-boson model by mapping the latter to the
interacting resonant level model
Transport properties of a periodically driven superconducting single electron transistor
We discuss coherent transport of Cooper pairs through a Cooper pair shuttle.
We analyze both the DC and AC Josephson effect in the two limiting cases where
the charging energy is either much larger or much smaller than the
Josephson coupling . In the limit we present the detailed
behavior of the critical current as a function of the damping rates and the
dynamical phases. The AC effect in this regime is very sensitive to all
dynamical scales present in the problem. The effect of fluctuations of the
external periodic driving is discussed as well. In the opposite regime the
system can be mapped onto the quantum kicked rotator, a classically chaotic
system. We investigate the transport properties also in this regime showing
that the underlying classical chaotic dynamics emerges as an incoherent
transfer of Cooper pairs through the shuttle. For an appropriate choice of the
parameters the Cooper pair shuttle can exhibit the phenomenon of dynamical
localization. We discuss in details the properties of the localized regime as a
function of the phase difference between the superconducting electrodes and the
decoherence due to gate voltage fluctuations. Finally we point how dynamical
localization is reflected in the noise properties of the shuttle.Comment: 22 pages, 7 figures; v3 (published version): added references,
improved readabilit
Solution of the Boltzmann equation in a random magnetic field
A general framework for solving the Boltzmann equation for a 2-dimensional
electron gas (2DEG) in random magnetic fields is presented, when the random
fields are included in the driving force. The formalism is applied to some
recent experiments, and a possible extension to composite fermions at
is discussed.Comment: 15 pages, Revtex 3.0. The 5 postscript figures can be obtained from
our WWW-server: http://roemer.fys.ku.dk/randbolt.htm , or on request from the
author
State-dependent impedance of a strongly coupled oscillator-qubit system
We investigate the measurements of two-state quantum systems (qubits) at
finite temperatures using a resonant harmonic oscillator as a quantum probe.
The reduced density matrix and oscillator correlators are calculated by a
scheme combining numerical methods with an analytical perturbation theory.
Correlators provide us information about the system impedance, which depends on
the qubit state. We show in detail how this property can be exploited in the
qubit measurement.Comment: 8 pages, 16 image
Suppression of the critical temperature of superconducting NdFeAs(OF) single crystals by Kondo-like defect sites induced by alpha-particle irradiation
We report a comprehensive investigation of the suppression of the critical
temperature Tc of NdFeAs(OF) single crystal by alpha-particle irradiation. Our
data indicate that irradiation defects produce both nonmagnetic and magnetic
scattering, resulting in the Kondo-like excess resistance over 2 decades in temperatures above . Despite high densities of
irradiation defects, the dose at which is suppressed to zero is
comparable to that for MgB2 but is well above the corresponding values for
cuprates.Comment: 11 pages, 4 figure
Counting statistics of interfering Bose-Einstein condensates
A method is presented that is able to predict the probability of outcomes of
snapshot measurements, such as the images of the instantaneous particle density
distribution in a quantum many-body system. It is shown that a gauge-like
transformation of the phase of the many-body wave function allows one to
construct a probability generating functional, the Fourier transform of which
with respect to the "gauge" field returns the joint probability distribution to
detect any given number of particles at various locations. The method is
applied to the problem of interference of two independent clouds of
Bose-Einstein condensates, where the initially separated clouds with fixed
boson numbers expand and the density profile image of the overlapping clouds is
registered. In the limit of large particle numbers, the probability to observe
a particular image of the density profile is shown to be given by a sum of
partial probability distributions, each of which corresponds to a noisy image
of interference of two matter waves with definite phase difference. In
agreement with earlier theoretical arguments, interference fringes are,
therefore, expected in any single shot measurement, the fringe pattern randomly
varying from run to run. These results conform to the physical picture where
the Bose-Einstein clouds are in spontaneously symmetry broken states, the
hidden phases of which are revealed by the density profile measurement via the
position of the interference fringes.Comment: Some changes in presentation, as published, 6 pages, LaTe
Divergence of the orbital nuclear magnetic relaxation rate in metals
We analyze the nuclear magnetic relaxation rate due to the
coupling of nuclear spin to the orbital moment of itinerant electrons in
metals. In the clean non--interacting case, contributions from large--distance
current fluctuations add up to cause a divergence of . When
impurity scattering is present, the elastic mean free time cuts off the
divergence, and the magnitude of the effect at low temperatures is controlled
by the parameter , where is the chemical potential. The
spin--dipolar hyperfine coupling, while has the same spatial variation
as the orbital hyperfine coupling, does not produce a divergence in the nuclear
magnetic relaxation rate.Comment: 11pages; v4: The analysis of the normal state is more compelete now,
including a comparison with other hyperfine interactions and a detailed
discussion of the effect in representative metals. The superconducting state
is excluded from consideration in this pape
- …