326 research outputs found
Modelling concentration fluctuation moments for spherically symmetric mean concentration
Clarke and Mole (Environmetrics, 6 (1995) 607-617) presented a model for concentration fluctuation moments of a passive scalar dispersing in a turbulent flow. This followed Sullivan and Moseley’s work in making use of the equation for the evolution of the concentration moments integrated over all space, together with Chatwin and
Sullivan’s (J. Fluid Mech., 212 (1990) 533-556) description relating higher moments to the mean concentration. The model incorporated a simple closure to express the concentration gradient in terms of the concentration. Numerical results were presented for 1, 2 and 3 spatial dimensions under the assumption that the spatial distribution of the mean concentration was spherically symmetric and Gaussian. Two simple functional forms were used for the spreading rate of the mean cloud. Here those results are briefly summarised. Some asymptotic large time results are also given for spherically symmetric mean concentration of general functional form, and numerical results are obtained for a number of different functional forms
Coordinated Spindle Assembly and Orientation Requires Clb5p-Dependent Kinase in Budding Yeast
The orientation of the mitotic spindle along a polarity axis is critical in asymmetric cell divisions. In the budding yeast, Saccharomyces cerevisiae, loss of the S-phase B-type cyclin Clb5p under conditions of limited cyclin-dependent kinase activity (cdc28-4 clb5Δ cells) causes a spindle positioning defect that results in an undivided nucleus entering the bud. Based on time-lapse digital imaging microscopy of microtubules labeled with green fluorescent protein fusions to either tubulin or dynein, we observed that the asymmetric behavior of the spindle pole bodies during spindle assembly was lost in the cdc28-4 clb5Δ cells. As soon as a spindle formed, both poles were equally likely to interact with the bud cell cortex. Persistent dynamic interactions with the bud ultimately led to spindle translocation across the bud neck. Thus, the mutant failed to assign one spindle pole body the task of organizing astral microtubules towards the mother cell. Our data suggest that Clb5p-associated kinase is required to confer mother-bound behavior to one pole in order to establish correct spindle polarity. In contrast, B-type cyclins, Clb3p and Clb4p, though partially redundant with Clb5p for an early role in spindle morphogenesis, preferentially promote spindle assembly
Edge effects and vertical stratification of aerial insectivorous bats across the interface of primary-secondary Amazonian rainforest
Research ArticleEdge effects, abiotic and biotic changes associated with habitat boundaries, are key drivers
of community change in fragmented landscapes. Their influence is heavily modulated by
matrix composition. With over half of the world’s tropical forests predicted to become forest
edge by the end of the century, it is paramount that conservationists gain a better understanding
of how tropical biota is impacted by edge gradients. Bats comprise a large fraction
of tropical mammalian fauna and are demonstrably sensitive to habitat modification. Yet,
knowledge about how bat assemblages are affected by edge effects remains scarce. Capitalizing
on a whole-ecosystem manipulation in the Central Amazon, the aims of this study
were to i) assess the consequences of edge effects for twelve aerial insectivorous bat species
across the interface of primary and secondary forest, and ii) investigate if the activity
levels of these species differed between the understory and canopy and if they were modulated
by distance from the edge. Acoustic surveys were conducted along four 2-km transects,
each traversing equal parts of primary and ca. 30-year-old secondary forest. Five
models were used to assess the changes in the relative activity of forest specialists (three
species), flexible forest foragers (three species), and edge foragers (six species). Modelling
results revealed limited evidence of edge effects, except for forest specialists in the understory.
No significant differences in activity were found between the secondary or primary forest
but almost all species exhibited pronounced vertical stratification. Previously defined bat
guilds appear to hold here as our study highlights that forest bats are more edge-sensitive
than edge foraging bats. The absence of pronounced edge effects and the comparable
activity levels between primary and old secondary forests indicates that old secondary forest can help ameliorate the consequences of fragmentation on tropical aerial insectivorous
batsinfo:eu-repo/semantics/publishedVersio
Investigating the Conformation of HER Membrane Proteins in Cells via Single Molecule and FLIM Microscopy
Ir(III) complexes of diamine ligands for asymmetric ketone hydrogenation
The use of a combination of IrCl3 with a series of ligands derived from the C2-symmetric diamine diphenylethanediamine (DPEN) forms a catalyst capable of the asymmetric hydrogenation of ketones in up to 85% ee
Neonatal encephalopathy: Case definition & guidelines for data collection, analysis, and presentation of maternal immunisation safety data.
To improve comparability of vaccine safety data, the acute neonatal encephalopathy working group has developed a case definition and guidelines neonatal encephalopathy applicable in study settings with different availability of resources, in healthcare settings that differ by availability of and access to health care, and in different geographic regions
Electromigration-Induced Flow of Islands and Voids on the Cu(001) Surface
Electromigration-induced flow of islands and voids on the Cu(001) surface is
studied at the atomic scale. The basic drift mechanisms are identified using a
complete set of energy barriers for adatom hopping on the Cu(001) surface,
combined with kinetic Monte Carlo simulations. The energy barriers are
calculated by the embedded atom method, and parameterized using a simple model.
The dependence of the flow on the temperature, the size of the clusters, and
the strength of the applied field is obtained. For both islands and voids it is
found that edge diffusion is the dominant mass-transport mechanism. The rate
limiting steps are identified. For both islands and voids they involve
detachment of atoms from corners into the adjacent edge. The energy barriers
for these moves are found to be in good agreement with the activation energy
for island/void drift obtained from Arrhenius analysis of the simulation
results. The relevance of the results to other FCC(001) metal surfaces and
their experimental implications are discussed.Comment: 9 pages, 13 ps figure
A probabilistic model for gene content evolution with duplication, loss, and horizontal transfer
We introduce a Markov model for the evolution of a gene family along a
phylogeny. The model includes parameters for the rates of horizontal gene
transfer, gene duplication, and gene loss, in addition to branch lengths in the
phylogeny. The likelihood for the changes in the size of a gene family across
different organisms can be calculated in O(N+hM^2) time and O(N+M^2) space,
where N is the number of organisms, is the height of the phylogeny, and M
is the sum of family sizes. We apply the model to the evolution of gene content
in Preoteobacteria using the gene families in the COG (Clusters of Orthologous
Groups) database
A complete 3D numerical study of the effects of pseudoscalar-photon mixing on quasar polarizations
We present the results of three-dimensional simulations of quasar
polarizations in the presence of pseudoscalar-photon mixing in the
intergalactic medium. The intergalactic magnetic field is assumed to be
uncorrelated in wave vector space but correlated in real space. Such a field
may be obtained if its origin is primordial. Furthermore we assume that the
quasars, located at cosmological distances, have negligible initial
polarization. In the presence of pseudoscalar-photon mixing we show, through a
direct comparison with observations, that this may explain the observed large
scale alignments in quasar polarizations within the framework of big bang
cosmology. We find that the simulation results give a reasonably good fit to
the observed data.Comment: 15 pages, 8 figures, significant changes, to appear in EPJ
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