27,709 research outputs found
Improving green manure quality with phosphate rocks in Ontario Canada
Phosphate rock (PR) was applied to one conventional and two organic dairy fields and planted with buckwheat (Fagopyrum esculentum) as a green manure crop. In total, five types of PR were applied at three application rates in order to determine the yield, concentration of P in the aboveground tissue and the P uptake of buckwheat. It was found that PR of relatively high carbonate substitution and small particle diameter could increase buckwheat tissue concentrations to a quality such that mineralization of the buckwheat mulch could occur. Buckwheat mulch and residual PR increased soil P flux as determined by anion exchange membranes in situ in the following spring. This provides evidence that buckwheat of high P quality has the potential to supply P to a subsequent crop
Dynamics and structure of an aging binary colloidal glass
We study aging in a colloidal suspension consisting of micron-sized particles
in a liquid. This system is made glassy by increasing the particle
concentration. We observe samples composed of particles of two sizes, with a
size ratio of 1:2.1 and a volume fraction ratio 1:6, using fast laser scanning
confocal microscopy. This technique yields real-time, three-dimensional movies
deep inside the colloidal glass. Specifically, we look at how the size, motion
and structural organization of the particles relate to the overall aging of the
glass. Particles move in spatially heterogeneous cooperative groups. These
mobile regions tend to be richer in small particles, and these small particles
facilitate the motion of nearby particles of both sizes.Comment: 7 pages; submitted to Phys. Rev. E. Revised with 1 new figure,
improved tex
Adaptive evolution of molecular phenotypes
Molecular phenotypes link genomic information with organismic functions,
fitness, and evolution. Quantitative traits are complex phenotypes that depend
on multiple genomic loci. In this paper, we study the adaptive evolution of a
quantitative trait under time-dependent selection, which arises from
environmental changes or through fitness interactions with other co-evolving
phenotypes. We analyze a model of trait evolution under mutations and genetic
drift in a single-peak fitness seascape. The fitness peak performs a
constrained random walk in the trait amplitude, which determines the
time-dependent trait optimum in a given population. We derive analytical
expressions for the distribution of the time-dependent trait divergence between
populations and of the trait diversity within populations. Based on this
solution, we develop a method to infer adaptive evolution of quantitative
traits. Specifically, we show that the ratio of the average trait divergence
and the diversity is a universal function of evolutionary time, which predicts
the stabilizing strength and the driving rate of the fitness seascape. From an
information-theoretic point of view, this function measures the
macro-evolutionary entropy in a population ensemble, which determines the
predictability of the evolutionary process. Our solution also quantifies two
key characteristics of adapting populations: the cumulative fitness flux, which
measures the total amount of adaptation, and the adaptive load, which is the
fitness cost due to a population's lag behind the fitness peak.Comment: Figures are not optimally displayed in Firefo
Two-Bit Messages are Sufficient to Implement Atomic Read/Write Registers in Crash-prone Systems
Atomic registers are certainly the most basic objects of computing science.
Their implementation on top of an n-process asynchronous message-passing system
has received a lot of attention. It has been shown that t \textless{} n/2
(where t is the maximal number of processes that may crash) is a necessary and
sufficient requirement to build an atomic register on top of a crash-prone
asynchronous message-passing system. Considering such a context, this paper
presents an algorithm which implements a single-writer multi-reader atomic
register with four message types only, and where no message needs to carry
control information in addition to its type. Hence, two bits are sufficient to
capture all the control information carried by all the implementation messages.
Moreover, the messages of two types need to carry a data value while the
messages of the two other types carry no value at all. As far as we know, this
algorithm is the first with such an optimality property on the size of control
information carried by messages. It is also particularly efficient from a time
complexity point of view
(2+1) resonant enhanced multiphoton ionization of H_2 via the E, F^(1)ÎŁ^+_g state
In this paper, we report the results of ab initio calculations of photoelectron angular distributions and vibrational branching ratios for the (2+1) REMPI of H_2 via the E, F^(1)ÎŁ^+_g state, and compare these with the experimental data of Anderson et al. [Chem. Phys. Lett. 105, 22 (1984)]. These results show that the observed nonâFranckâCondon behavior is predominantly due to the R dependence of the transition matrix elements, and to a lesser degree to the energy dependence. This work presents the first molecular REMPI study employing a correlated wave function to describe the Rydbergâvalence mixing in the resonant intermediate state
Legumes as a Biological Tool to Address the Sustainability of Ruminant Production Systems
Growing public concern regarding accelerated rates of climate change, the depletion and degradation of natural resources such as biodiversity water and soils, coupled with policy commitments to address these challenges, are placing increasing pressures to enhance sustainability metrics associated with agriculture in general, and ruminant production systems in particular. At EU and indeed global scale, there has probably never before been so many potentially conflicting challenges for agriculture. On one hand, agricultural systems need to produce more, to feed the increasing global human population, while at the same time being much less reliant on economically and environmentally costly chemical inputs and protecting natural resources. Within this paper we provide an overview of recent research that demonstrates the potential contributions that legume inclusion within grass swards can make to developing more sustainable and resilient ruminant productions systems
The statistical mechanics of a polygenic characterunder stabilizing selection, mutation and drift
By exploiting an analogy between population genetics and statistical
mechanics, we study the evolution of a polygenic trait under stabilizing
selection, mutation, and genetic drift. This requires us to track only four
macroscopic variables, instead of the distribution of all the allele
frequencies that influence the trait. These macroscopic variables are the
expectations of: the trait mean and its square, the genetic variance, and of a
measure of heterozygosity, and are derived from a generating function that is
in turn derived by maximizing an entropy measure. These four macroscopics are
enough to accurately describe the dynamics of the trait mean and of its genetic
variance (and in principle of any other quantity). Unlike previous approaches
that were based on an infinite series of moments or cumulants, which had to be
truncated arbitrarily, our calculations provide a well-defined approximation
procedure. We apply the framework to abrupt and gradual changes in the optimum,
as well as to changes in the strength of stabilizing selection. Our
approximations are surprisingly accurate, even for systems with as few as 5
loci. We find that when the effects of drift are included, the expected genetic
variance is hardly altered by directional selection, even though it fluctuates
in any particular instance. We also find hysteresis, showing that even after
averaging over the microscopic variables, the macroscopic trajectories retain a
memory of the underlying genetic states.Comment: 35 pages, 8 figure
Time-Efficient Read/Write Register in Crash-prone Asynchronous Message-Passing Systems
The atomic register is certainly the most basic object of computing science.
Its implementation on top of an n-process asynchronous message-passing system
has received a lot of attention. It has been shown that t \textless{} n/2
(where t is the maximal number of processes that may crash) is a necessary and
sufficient requirement to build an atomic register on top of a crash-prone
asynchronous message-passing system. Considering such a context, this paper
visits the notion of a fast implementation of an atomic register, and presents
a new time-efficient asynchronous algorithm. Its time-efficiency is measured
according to two different underlying synchrony assumptions. Whatever this
assumption, a write operation always costs a round-trip delay, while a read
operation costs always a round-trip delay in favorable circumstances
(intuitively, when it is not concurrent with a write). When designing this
algorithm, the design spirit was to be as close as possible to the one of the
famous ABD algorithm (proposed by Attiya, Bar-Noy, and Dolev)
Bulk photonic metamaterial with hyperbolic dispersion
In this work, we demonstrate a self-standing bulk three-dimensional
metamaterial based on the network of silver nanowires in an alumina membrane.
This constitutes an anisotropic effective medium with hyperbolic dispersion,
which can be used in sub-diffraction imaging or optical cloaks. Highly
anisotropic dielectric constants of the material range from positive to
negative, and the transmitted laser beam shifts both toward the normal to the
surface, as in regular dielectrics, and off the normal, as in anisotropic
dielectrics with the refraction index smaller than one. The designed photonic
metamaterial is the thickest reported in the literature, both in terms of its
physical size 1cm x 1cm x 51 mm, and the number of vacuum wavelengths, N=61 at
l=0.84 mm.Comment: 6 pages, 4 figur
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