8,139 research outputs found
The gene complement of the ancestral bilaterian - was Urbilateria a monster?
Expressed sequence tag analyses of the annelid Pomatoceros lamarckii, recently published in BMC Evolutionary Biology, are consistent with less extensive gene loss in the Lophotrochozoa than in the Ecdysozoa, but it would be premature to generalize about patterns of gene loss on the basis of the limited data available
Epidemics on random intersection graphs
In this paper we consider a model for the spread of a stochastic SIR
(Susceptible Infectious Recovered) epidemic on a network of
individuals described by a random intersection graph. Individuals belong to a
random number of cliques, each of random size, and infection can be transmitted
between two individuals if and only if there is a clique they both belong to.
Both the clique sizes and the number of cliques an individual belongs to follow
mixed Poisson distributions. An infinite-type branching process approximation
(with type being given by the length of an individual's infectious period) for
the early stages of an epidemic is developed and made fully rigorous by proving
an associated limit theorem as the population size tends to infinity. This
leads to a threshold parameter , so that in a large population an epidemic
with few initial infectives can give rise to a large outbreak if and only if
. A functional equation for the survival probability of the
approximating infinite-type branching process is determined; if , this
equation has no nonzero solution, while if , it is shown to have
precisely one nonzero solution. A law of large numbers for the size of such a
large outbreak is proved by exploiting a single-type branching process that
approximates the size of the susceptibility set of a typical individual.Comment: Published in at http://dx.doi.org/10.1214/13-AAP942 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Differential expression of three galaxin-related genes during settlement and metamorphosis in the scleractinian coral Acropora millepora
BACKGROUND: The coral skeleton consists of CaCO3 deposited upon an organic matrix primarily
as aragonite. Currently galaxin, from Galaxea fascicularis, is the only soluble protein component of
the organic matrix that has been characterized from a coral. Three genes related to galaxin were
identified in the coral Acropora millepora.
RESULTS: One of the Acropora genes (Amgalaxin) encodes a clear galaxin ortholog, while the others
(Amgalaxin-like 1 and Amgalaxin-like 2) encode larger and more divergent proteins. All three
proteins are predicted to be extracellular and share common structural features, most notably the
presence of repetitive motifs containing dicysteine residues. In situ hybridization reveals distinct,
but partially overlapping, spatial expression of the genes in patterns consistent with distinct roles
in calcification. Both of the Amgalaxin-like genes are expressed exclusively in the early stages of
calcification, while Amgalaxin continues to be expressed in the adult, consistent with the situation
in the coral Galaxea.
CONCLUSION: Comparisons with molluscs suggest functional convergence in the two groups; lustrin
A/pearlin proteins may be the mollusc counterparts of galaxin, whereas the galaxin-like proteins
combine characteristics of two distinct proteins involved in mollusc calcification. Database searches
indicate that, although sequences with high similarity to the galaxins are restricted to the
Scleractinia, more divergent members of this protein family are present in other cnidarians and
some other metazoans. We suggest that ancestral galaxins may have been secondarily recruited to
roles in calcification in the Triassic, when the Scleractinia first appeared. Understanding the
evolution of the broader galaxin family will require wider sampling and expression analysis in a
range of cnidarians and other animals
Household epidemic models with varying infection response
This paper is concerned with SIR (susceptible--infected--removed) household epidemic models in which the infection response may be either mild or severe, with the type of response also affecting the infectiousness of an individual. Two different models are analysed. In the first model, the infection status of an individual is predetermined, perhaps due to partial immunity, and in the second, the infection status of an individual depends on the infection status of its infector and on whether the individual was infected by a within- or between-household contact. The first scenario may be modelled using a multitype household epidemic model, and the second scenario by a model we denote by the infector-dependent-severity household epidemic model. Large population results of the two models are derived, with the focus being on the distribution of the total numbers of mild and severe cases in a typical household, of any given size, in the event that the epidemic becomes established. The aim of the paper is to investigate whether it is possible to determine which of the two underlying explanations is causing the varying response when given final size household outbreak data containing mild and severe cases. We conduct numerical studies which show that, given data on sufficiently many households, it is generally possible to discriminate between the two models by comparing the Kullback-Leibler divergence for the two fitted models to these data
An SIR epidemic model on a population with random network and household structure and several types of individuals
We consider a stochastic SIR (susceptible → infective → removed) epidemic model with several types of individuals. Infectious individuals can make infectious contacts on two levels, within their own ‘household’ and with their neighbours in a random graph representing additional social contacts. This random graph is an extension of the well-known configuration model to allow for several types of individuals. We give a strong approximation theorem which leads to a threshold theorem for the epidemic model and a method for calculating the probability of a major outbreak given few initial infectives. A multitype analogue of a theorem of Ball et al. (2009) heuristically
motivates a method for calculating the expected size of such a major outbreak. We also consider vaccination and give some short numerical illustrations of our results
The gene complement of the ancestral bilaterian - was Urbilateria a monster?
Expressed sequence tag analyses of the annelid Pomatoceros lamarckii, recently published in BMC Evolutionary Biology, are consistent with less extensive gene loss in the Lophotrochozoa than in the Ecdysozoa, but it would be premature to generalize about patterns of gene loss on the basis of the limited data available
Matrix isolation as a tool for studying interstellar chemical reactions
Since the identification of the OH radical as an interstellar species, over 50 molecular species were identified as interstellar denizens. While identification of new species appears straightforward, an explanation for their mechanisms of formation is not. Most astronomers concede that large bodies like interstellar dust grains are necessary for adsorption of molecules and their energies of reactions, but many of the mechanistic steps are unknown and speculative. It is proposed that data from matrix isolation experiments involving the reactions of refractory materials (especially C, Si, and Fe atoms and clusters) with small molecules (mainly H2, H2O, CO, CO2) are particularly applicable to explaining mechanistic details of likely interstellar chemical reactions. In many cases, matrix isolation techniques are the sole method of studying such reactions; also in many cases, complexations and bond rearrangements yield molecules never before observed. The study of these reactions thus provides a logical basis for the mechanisms of interstellar reactions. A list of reactions is presented that would simulate interstellar chemical reactions. These reactions were studied using FTIR-matrix isolation techniques
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