1,248 research outputs found
Examining the nutrient dynamics of willow biomass energy plantations
Non-Peer ReviewedNatural Resources Canada, along with a number of Canadian provinces, considers bioenergy to be a legitimate and sustainable source of energy that will constitute a significant portion of future energy production. Shrub willow (Salix spp.) is a proven viable purpose-grown bioenergy feedstock. The objective of this four-year study was to examine the cycling of nitrogen, phosphorus, potassium, and sulphur within several high density willow stands during the first rotation, in order to forecast the long-term sustainability of these woody crop plantations grown on numerous soil types in Saskatchewan. Soil and plant samples were collected throughout the rotation and analyzed for their nutrient content. The results of this study indicate that sites with relatively fertile soils are more capable of sustaining willow productivity for multiple rotations compared to sites with marginal soils, where supplemental fertility will be required to sustain long-term production levels. Ensuring optimal soil fertility will help promote the sustainability of these purpose-grown biomass energy plantations
Scaling behavior of the directed percolation universality class
In this work we consider five different lattice models which exhibit
continuous phase transitions into absorbing states. By measuring certain
universal functions, which characterize the steady state as well as the
dynamical scaling behavior, we present clear numerical evidence that all models
belong to the universality class of directed percolation. Since the considered
models are characterized by different interaction details the obtained
universal scaling plots are an impressive manifestation of the universality of
directed percolation.Comment: 24 pages, 7 figures, accepted for publication in Nuclear Physics
Changes in Climate and Potential Evapotranspiration Across a Large Irrigated Area in Idaho
Ground level climatic measurements
were taken along a 50
km transect going from dry sagebrush
land into the center of a large
irrigated area in southern Idaho.
Measurements in May, when the
desert area was dry, indicated
that climatic changes across the
transect were minimal. In August,
when the desert was obviously very
dry, air temperatures decreased,
vapor pressure increased, and
windspeed was reduced about
40 percent within the irrigated
area. The results demonstrate
that any weather service agency or
group must consider the distance
from dry surroundings when selecting
sites that are to be representative of
climatic conditions over irrigated
fields
Screening current effects in Josephson junction arrays
The purpose of this work is to compare the dynamics of arrays of Josephson
junctions in presence of magnetic field in two different frameworks: the so
called XY frustrated model with no self inductance and an approach that takes
into account the screening currents (considering self inductances only). We
show that while for a range of parameters the simpler model is sufficiently
accurate, in a region of the parameter space solutions arise that are not
contained in the XY model equations.Comment: Figures available from the author
Policy instruments and welfare state reform
A core, but so far untested, proposition of the new politics perspective, originally introduced by Paul
Pierson, is that welfare state cutbacks will be implemented using so-called âinvisibleâ policy instruments,
for example, a change in indexation rules. Expansion should, by implication, mainly happen using âvisibleâ
policy instruments, for example, a change in nominal benefits. We have coded 1030 legislative reforms of
old-age pensions and unemployment protection in Britain, Denmark, Finland and Germany from 1974 to
2014. With this unique data at hand, we find substantial support for this crucial new politics proposition
Phase transition and selection in a four-species cyclic Lotka-Volterra model
We study a four species ecological system with cyclic dominance whose
individuals are distributed on a square lattice. Randomly chosen individuals
migrate to one of the neighboring sites if it is empty or invade this site if
occupied by their prey. The cyclic dominance maintains the coexistence of all
the four species if the concentration of vacant sites is lower than a threshold
value. Above the treshold, a symmetry breaking ordering occurs via growing
domains containing only two neutral species inside. These two neutral species
can protect each other from the external invaders (predators) and extend their
common territory. According to our Monte Carlo simulations the observed phase
transition is equivalent to those found in spreading models with two equivalent
absorbing states although the present model has continuous sets of absorbing
states with different portions of the two neutral species. The selection
mechanism yielding symmetric phases is related to the domain growth process
whith wide boundaries where the four species coexist.Comment: 4 pages, 5 figure
Josephson flux-flow oscillators in nonuniform microwave fields
We present a simple theory for Josephson flux-flow oscillators in the presence of nonuniform microwave fields. In particular we derive an analytical expression for the IâV characteristic of the oscillator from which we show that satellite steps are spaced around the main flux-flow resonance by only even harmonics of the rf frequency. This result is found to be in good agreement with our numerical results and with experiments
Bias and temperature dependence of the 0.7 conductance anomaly in Quantum Point Contacts
The 0.7 (2e^2/h) conductance anomaly is studied in strongly confined, etched
GaAs/GaAlAs quantum point contacts, by measuring the differential conductance
as a function of source-drain and gate bias as well as a function of
temperature. We investigate in detail how, for a given gate voltage, the
differential conductance depends on the finite bias voltage and find a
so-called self-gating effect, which we correct for. The 0.7 anomaly at zero
bias is found to evolve smoothly into a conductance plateau at 0.85 (2e^2/h) at
finite bias. Varying the gate voltage the transition between the 1.0 and the
0.85 (2e^2/h) plateaus occurs for definite bias voltages, which defines a gate
voltage dependent energy difference . This energy difference is
compared with the activation temperature T_a extracted from the experimentally
observed activated behavior of the 0.7 anomaly at low bias. We find \Delta =
k_B T_a which lends support to the idea that the conductance anomaly is due to
transmission through two conduction channels, of which the one with its subband
edge \Delta below the chemical potential becomes thermally depopulated as the
temperature is increased.Comment: 9 pages (RevTex) with 9 figures (some in low resolution
Can filesharers be triggered by economic incentives? Results of an experiment
Illegal filesharing on the internet leads to considerable financial losses for artists and copyright owners as well as producers and sellers of music. Thus far, measures to contain this phenomenon have been rather restrictive. However, there are still a considerable number of illegal systems, and users are able to decide quite freely between legal and illegal downloads because the latter are still difficult to sanction. Recent economic approaches account for the improved bargaining position of users. They are based on the idea of revenue-splitting between professional sellers and peers. In order to test such an innovative business model, the study reported in this article carried out an experiment with 100 undergraduate students, forming five small peer-to-peer networks.The networks were confronted with different economic conditions.The results indicate that even experienced filesharers hold favourable attitudes towards revenue-splitting.They seem to be willing to adjust their behaviour to different economic conditions
Dynamic Vortex Phases and Pinning in Superconductors with Twin Boundaries
We investigate the pinning and driven dynamics of vortices interacting with
twin boundaries using large scale molecular dynamics simulations on samples
with near one million pinning sites. For low applied driving forces, the vortex
lattice orients itself parallel to the twin boundary and we observe the
creation of a flux gradient and vortex free region near the edges of the twin
boundary. For increasing drive, we find evidence for several distinct dynamical
flow phases which we characterize by the density of defects in the vortex
lattice, the microscopic vortex flow patterns, and orientation of the vortex
lattice. We show that these different dynamical phases can be directly related
to microscopically measurable voltage - current V(I) curves and voltage noise.
By conducting a series of simulations for various twin boundary parameters we
derive several vortex dynamic phase diagrams.Comment: 5 figures, to appear in Phys. Rev.
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