239 research outputs found
The Influence of Sporulation Conditions on the Spore Coat Protein Composition of <em>Bacillus subtilis</em> Spores
Activated Random Walkers: Facts, Conjectures and Challenges
We study a particle system with hopping (random walk) dynamics on the integer
lattice . The particles can exist in two states, active or
inactive (sleeping); only the former can hop. The dynamics conserves the number
of particles; there is no limit on the number of particles at a given site.
Isolated active particles fall asleep at rate , and then remain
asleep until joined by another particle at the same site. The state in which
all particles are inactive is absorbing. Whether activity continues at long
times depends on the relation between the particle density and the
sleeping rate . We discuss the general case, and then, for the
one-dimensional totally asymmetric case, study the phase transition between an
active phase (for sufficiently large particle densities and/or small )
and an absorbing one. We also present arguments regarding the asymptotic mean
hopping velocity in the active phase, the rate of fixation in the absorbing
phase, and survival of the infinite system at criticality. Using mean-field
theory and Monte Carlo simulation, we locate the phase boundary. The phase
transition appears to be continuous in both the symmetric and asymmetric
versions of the process, but the critical behavior is very different. The
former case is characterized by simple integer or rational values for critical
exponents (, for example), and the phase diagram is in accord with
the prediction of mean-field theory. We present evidence that the symmetric
version belongs to the universality class of conserved stochastic sandpiles,
also known as conserved directed percolation. Simulations also reveal an
interesting transient phenomenon of damped oscillations in the activity
density
Monitoring van groene burgerinitiatieven : analyse van de resultaten van een pilot en nulmeting in vier gemeenten
To inform the evaluation of the Nature Pact (Natuurpact) and the Assessment of the Dutch Human Environment (Balans van de Leefomgeving), PBL Netherlands Environmental Assessment Agency needs a quantitative measure of the size and scope of green citizens’ initiatives and their impact. The need for this information reflects the ambition of many government authorities to bring the wider community, including individuals, into closer contact with nature and involve them more in nature policy. This report describes the results of a baseline assessment and pilot study to test the newly developed methodology for monitoring green citizens’ initiatives. Besides the results, the report includes several analyses based on the data and presents the main findings
Evolutionary phase space in driven elliptical billiards
We perform the first long-time exploration of the classical dynamics of a
driven billiard with a four dimensional phase space. With increasing velocity
of the ensemble we observe an evolution from a large chaotic sea with
stickiness due to regular islands to thin chaotic channels with diffusive
motion leading to Fermi acceleration. As a surprising consequence, we encounter
a crossover, which is not parameter induced but rather occurs dynamically, from
amplitude dependent tunable subdiffusion to universal normal diffusion in
momentum space. In the high velocity case we observe particle focusing in phase
space.Comment: 5 pages, 4 figure
Intraspecific variability of popcorn S7 lines for phosphorus efficiency in the soil.
The expansion of agriculture, coupled with the need for sustainable cropping, is one of the greatest challenges of the scientific community working on the generation of new cultivars adapted to abiotic stress conditions. The aim of this study was to evaluate the variability of popcorn lines as to responsiveness and efficiency in phosphorus use, as a first step towards the implementation of a breeding program interested in the practice of sustainable agriculture. Twenty-five popcorn lines were evaluated in two locations with different phosphorus levels in the soil, using a randomized block design. The following traits were measured: plant height, ear height, female flowering date, male flowering date, male-female flowering interval, ear diameter, ear length, 100-grain weight, grain yield, popping expansion, and expanded popcorn volume per hectare. A combined analysis of variance and test of means were performed, and the lines were classified as to their phosphorus use efficiency, according to their production performance in the different environments. The genetic diversity between the lines was estimated by Tocher?s and UPGMA clustering methods, using generalized Mahalanobis distance. Lines L59, P7, P2, P3, P4, P8, P10, P9, L66, L70, L69, and P5 were efficient and responsive, whereas lines L75, L80, L61, L77, L63, L65, P1, L54, L53, L88, and L71 were inefficient and nonresponsive. Genetic variability was greater in the environments with low phosphorus in the soil, suggesting that the selection pressure exerted in the stressing environment is a decisive factor to obtain a higher expression of variability
Genetic effects on the efficiency and responsiveness to phosphorus use in popcorn as estimated by diallel analysis.
Agricultural expansion and the need for sustainable cultivation are challenges faced by researchers involved in the generation of new cultivars that can adapt to abiotic stress. Knowledge of the genetic effects of characteristics related to efficiency and responsiveness to phosphorus use must be considered when implementing methods to obtain better genotypes. The aim of this study was to characterize and select popcorn hybrids based on their efficiency and responsiveness to phosphorus use, and estimate their combining abilities and genetic effects via diallel analysis to implement improvement programs for sustainable agriculture. Eight contrasting inbred lines were used to obtain simple hybrids for diallel analysis. Twenty-eight diallelic hybrids plus the popcorn parental lines were evaluated at two different sites under two contrasting environments for soil phosphorus availability (6Ă—6 lattice design). Grain yield, popping expansion, and volume of expanded popcorn per hectare were measured. A combined analysis of variance and a test of means were performed. The classification and utilization of the phosphorus use efficiency index, according to the grain yield performance of the hybrids under contrasting environments, was considered. Through model 2 of the Griffing?s diallel analysis method, the general and specific combining abilities were estimated, along with their environmental interactions. The best strategy to obtain genotypes that are efficient and responsive to phosphorus involves exploring popcorn hybrids using genitors that result in the accumulation of additive genes that promote popping expansion. Hybrids P7Ă—L80, P7Ă—L59, P7Ă—L76, and P6Ă—L80 presented promising results and may be evaluated as cultivation options in phosphorus-deficient soils
Pair contact process with a particle source
We study the phase diagram and critical behavior of the one-dimensional pair
contact process (PCP) with a particle source using cluster approximations and
extensive simulations. The source creates isolated particles only, not pairs,
and so couples not to the order parameter (the pair density) but to a
non-ordering field, whose state influences the evolution of the order
parameter. While the critical point p_c shows a singular dependence on the
source intensity, the critical exponents appear to be unaffected by the
presence of the source, except possibly for a small change in beta. In the
course of our study we obtain high-precision values for the critical exponents
of the standard PCP, confirming directed-percolation-like scaling.Comment: 15 pages, 9 figure
The non-equilibrium phase transition of the pair-contact process with diffusion
The pair-contact process 2A->3A, 2A->0 with diffusion of individual particles
is a simple branching-annihilation processes which exhibits a phase transition
from an active into an absorbing phase with an unusual type of critical
behaviour which had not been seen before. Although the model has attracted
considerable interest during the past few years it is not yet clear how its
critical behaviour can be characterized and to what extent the diffusive
pair-contact process represents an independent universality class. Recent
research is reviewed and some standing open questions are outlined.Comment: Latexe2e, 53 pp, with IOP macros, some details adde
Universal finite-size scaling amplitudes in anisotropic scaling
Phenomenological scaling arguments suggest the existence of universal
amplitudes in the finite-size scaling of certain correlation lengths in
strongly anisotropic or dynamical phase transitions. For equilibrium systems,
provided that translation invariance and hyperscaling are valid, the
Privman-Fisher scaling form of isotropic equilibrium phase transitions is
readily generalized. For non-equilibrium systems, universality is shown
analytically for directed percolation and is tested numerically in the
annihilation-coagulation model and in the pair contact process with diffusion.
In these models, for both periodic and free boundary conditions, the
universality of the finite-size scaling amplitude of the leading relaxation
time is checked. Amplitude universality reveals strong transient effects along
the active-inactive transition line in the pair contact process.Comment: 16 pages, Latex, 2 figures, final version, to appear in J. Phys.
Metabolomics guided pathway analysis reveals link between cancer metastasis, cholesterol sulfate, and phospholipids
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