2,347 research outputs found
An automatic adaptive method to combine summary statistics in approximate Bayesian computation
To infer the parameters of mechanistic models with intractable likelihoods,
techniques such as approximate Bayesian computation (ABC) are increasingly
being adopted. One of the main disadvantages of ABC in practical situations,
however, is that parameter inference must generally rely on summary statistics
of the data. This is particularly the case for problems involving
high-dimensional data, such as biological imaging experiments. However, some
summary statistics contain more information about parameters of interest than
others, and it is not always clear how to weight their contributions within the
ABC framework. We address this problem by developing an automatic, adaptive
algorithm that chooses weights for each summary statistic. Our algorithm aims
to maximize the distance between the prior and the approximate posterior by
automatically adapting the weights within the ABC distance function.
Computationally, we use a nearest neighbour estimator of the distance between
distributions. We justify the algorithm theoretically based on properties of
the nearest neighbour distance estimator. To demonstrate the effectiveness of
our algorithm, we apply it to a variety of test problems, including several
stochastic models of biochemical reaction networks, and a spatial model of
diffusion, and compare our results with existing algorithms
The impact of temporal sampling resolution on parameter inference for biological transport models
Imaging data has become widely available to study biological systems at
various scales, for example the motile behaviour of bacteria or the transport
of mRNA, and it has the potential to transform our understanding of key
transport mechanisms. Often these imaging studies require us to compare
biological species or mutants, and to do this we need to quantitatively
characterise their behaviour. Mathematical models offer a quantitative
description of a system that enables us to perform this comparison, but to
relate these mechanistic mathematical models to imaging data, we need to
estimate the parameters of the models. In this work, we study the impact of
collecting data at different temporal resolutions on parameter inference for
biological transport models by performing exact inference for simple velocity
jump process models in a Bayesian framework. This issue is prominent in a host
of studies because the majority of imaging technologies place constraints on
the frequency with which images can be collected, and the discrete nature of
observations can introduce errors into parameter estimates. In this work, we
avoid such errors by formulating the velocity jump process model within a
hidden states framework. This allows us to obtain estimates of the
reorientation rate and noise amplitude for noisy observations of a simple
velocity jump process. We demonstrate the sensitivity of these estimates to
temporal variations in the sampling resolution and extent of measurement noise.
We use our methodology to provide experimental guidelines for researchers
aiming to characterise motile behaviour that can be described by a velocity
jump process. In particular, we consider how experimental constraints resulting
in a trade-off between temporal sampling resolution and observation noise may
affect parameter estimates.Comment: Published in PLOS Computational Biolog
Increased productivity of Clostridium acetobutylicum fermentation of acetone, butanol, and ethanol by pervaporation through supported ionic liquid membrane
Pervaporation proved to be one of the best methods to remove solvents out of a solvent producing Clostridium acetobutylicum culture. By using an ionic liquid (IL)-polydimethylsiloxane (PDMS) ultrafiltration membrane (pore size 60 nm), we could guarantee high stability and selectivity during all measurements carried out at 37C. Overall solvent productivity of fermentation connected with continuous product removal by pervaporation was 2.34 g l(-1) h(-1). The supported ionic liquid membrane (SILM) was impregnated with 15 wt% of a novel ionic liquid (tetrapropylammonium tetracyano-borate) and 85 wt% of polydimethylsiloxane. Pervaporation, accomplished with the optimized SILM, led to stable and efficient removal of the solvents butan-1-ol and acetone out of a C. acetobutylicum culture. By pervaporation through SILM, we removed more butan-1-ol than C. acetobutylicum was able to produce. Therefore, we added an extra dose of butan-1-ol to run fermentation on limiting values where the bacteria would still be able to survive its lethal concentration (15.82 g/l). After pervaporation was switched off, the bacteria died from high concentration of butan-1-ol, which they produced
Characteristics and causes of severe poverty and hunger:
Poverty reduction, Poverty, Hunger, Landlessness in rural areas, Poverty dynamics, Measuring severe poverty, Characteristics of poor and hungry, Women,
Nonthermal Radio Emission from Planetary Nebulae
In a recent analysis of the radio emission from the planetary nebula A30,
Dgani, Evans & White (1998) claim that the emission, located in the inner
region, is probably dominated by nonthermal emission.
We propose a model to explain this.
We assume that the fast wind, blown by the central star of A30 carries a very
weak magnetic field. The interaction of this wind with a cluster of dense
condensations traps the magnetic field lines for a long time and stretches
them, leading to a strong magnetic field.
If relativistic particles are formed as the fast wind is shocked, then the
enhanced magnetic field will result in nonthermal radio emission.
The typical nonthermal radio flux at 1 GHz can be up to several milli-Jansky.
In order to detect the nonthermal emission, the emitting region should be
spatially resolved from the main optical nebula.
We list other planetary nebulae which may possess nonthermal radio emission.Comment: 11 page
Form factors for semi-leptonic B decays
We report on form factors for the B->K l^+ l^- semi-leptonic decay process.
We use several lattice spacings from a=0.12 fm down to 0.06 fm and a variety of
dynamical quark masses with 2+1 flavors of asqtad quarks provided by the MILC
Collaboration. These ensembles allow good control of the chiral and continuum
extrapolations. The b-quark is treated as a clover quark with the Fermilab
interpretation. We update our results for f_\parallel and f_\perp, or,
equivalently, f_+ and f_0. In addition, we present new results for the tensor
form factor f_T. Model independent results are obtained based upon the
z-expansion.Comment: 7 pages, 4 figures, presented at The XXXth International Symposium on
Lattice Field Theory - Lattice 2012, June 24-29, 2012 Cairns, Australia, to
appear as PoS(Lattice 2012)12
Global monopoles in dilaton gravity
We analyse the gravitational field of a global monopole within the context of
low energy string gravity, allowing for an arbitrary coupling of the monopole
fields to the dilaton. Both massive and massless dilatons are considered. We
find that, for a massless dilaton, the spacetime is generically singular,
whereas when the dilaton is massive, the monopole generically induces a long
range dilaton cloud. We compare and contrast these results with the literature.Comment: 15 pages, 3 figures, version to appear in Class Quant Gra
Family Distress and Eating Disorders among Undergraduate Students of University of Port Harcourt, Rivers State, Nigeria
The study investigated the relative relationship between family distress and eating disorders among undergraduate students of University of Port Harcourt. The study was guided by three research questions and three null hypotheses to test the tenability of the independent variables on the dependent variable at 0.05 level of significance. The study adopted correlation research design. A sample of 388 was drawn from a population of 14,000 undergraduate students of University of Port Harcourt (predominantly 100 and 200) level, using simple random and purposive sampling techniques. The instruments for data collection were Eating Attitude Test (EAT) and questionnaire for family distress which were validated by experts. The reliability of the instruments was ascertained to be 0.73. Mean and Standard deviation statistics were used to answer the research questions while Pearson product moment correlation analysis was used to test the null hypothesis. The study revealed that there is a relationship between the independent variable and the dependent variable while hypothesis 2 was not statistically significant. It was also revealed that, hypothesis 3 was statistically significant indicating an existence influence of the independent variable on the dependent variable. It was recommended that parents, educational institutions and the government should wake up to their responsibilities of teaching certain aspects of eating attitude in order to curb the danger inherent in eating disorders. Keywords: Family, Distress, Eating, Disorders, Anorexia, Bulimia, Bing
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