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| 2. |
- Olsson, Urban, 1954, et al.
(författare)
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The Lanius excubitor (Aves, Passeriformes) conundrum – Taxonomic dilemma when molecular and non-molecular data tell different stories.
- 2010
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Ingår i: Molecular Phylogenetics and Evolution. - : Elsevier BV. - 1055-7903 .- 1095-9513. ; 55:2, s. 347-357
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Tidskriftsartikel (refereegranskat)abstract
- The phylogeny of 18 taxa in the Lanius excubitor complex, and the related species L. sphenocercus, L. ludovicianus and L. somalicus, was estimated based on the mitochondrial cytochrome b gene and the non-coding D-loop (in total ∼1.3 kb). According to the mitochondrial gene tree, Lanius excubitor s.l. is non-monophyletic, with some of its subspecies being more closely related to L. sphenocercus, L. ludovicianus, and L. somalicus. Also the division of the L. excubitor complex into a northern (L. excubitor) and a southern (L. meridionalis) species, as has been proposed based on morphological and ecological similarity and geographical distributions, is not compatible with the mitochondrial tree. Overall, genetic divergences among the ingroup taxa are small, indicating a recent radiation. A tree based on the nuclear ornithine decarboxylase (ODC) introns 6–7 is unresolved with respect to the ingroup, but provides strong support for a clade containing the Lanius excubitor complex, L. sphenocercus, L. ludovicianus and L. somalicus. We discuss the incongruence between the current taxonomy and the mitochondrial gene tree, and conclude that based on the latter the Lanius excubitor complex may be treated as at least six species, L. borealis, L. elegans, L. excubitor, L. lahtora, L. meridionalis, and L. uncinatus, but that other taxonomic treatments are also possible. However, uncertainty regarding to which extent the mitochondrial gene tree reflects the species phylogeny prevents us from recommending taxonomic change without further investigation. This study highlights the possible danger of relying on a single molecular marker, such as mitochondrial DNA, in taxonomic revisions and phylogenetic inference
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| 3. |
- Tapani, Sofia, 1982
(författare)
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Stochastic modelling and analysis of early mouse development
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis is to model and describe dynamical events for biological cells using statistical and mathematical tools. The thesis includes five papers that all relate to stochastic modelling of cells. In order to understand the development and patterning of the early mammalian embryo, stochastic modelling has become a more important tool than ever. It allows for studying the processes that mediate the transition from pluripotency of the embryonic cells to their differentiation. It is still unclear whether the positions of cells determine their future fates. One alternative possibility is that cells are pre-specified at random positions and then sort according to a already set fate. Mouse embryonic cells are thought to be equivalent in their developmental properties until approaching the eight-cell stage. Some biological studies show, in comparison, that patterning can be present already at sperm entry and in the pronuclei migration. We investigate in Paper I the dynamics of the pronuclei migration by analysing their trajectories and find that not only do the pronuclei follow a noise corrupted path towards the centre of the egg but they also have some attraction to each other which affects their dynamics. Continuing in Paper II and III, we use these results to model this behaviour with a coupled stochastic differential equation model. This enables us to simulate distributions that describe the meeting plane between pronuclei which in turn can be related to the orientation of the first cleavage of the egg. Our results show that adding randomness in sperm entry point is different from the randomness added through the environment of the egg. We are also able to show that data sets with normal eggs and eggs treated with an actin growth inhibitor give rise to considerably different model dynamics, suggesting that the treatment is affecting the migration in an invasive way. Altering the pronuclei dynamics can alter the polarity of the egg and may transfer into the later axis-formation process. Invasiveness of experimental procedures is a difficult issue to handle. The alternative to invasive procedures is not appealing since it means that important developmental features may not be discovered because of individual variability and noise, leading to guesswork of the underlying mechanisms. The embryonic cells are easily affected by treatments performed to make the measuring, made by hand, easier or by the light exposure of the microscope. Treatments as such are used for example for producing flourescent proteins in membranes or slowing processes down. Paper IV and Paper V serve to analyse how light induced stress affects yeast cells and we employ a method for analysing the noisy non-stationary time series, which are a result of the yeast experiments, using wavelet decomposition.
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| 5. |
- Backhaus, Thomas, 1967
(författare)
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Interactions and their impact on the applicability of Concentration Addition for environmentally realistic mixtures
- 2011
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Ingår i: Ecosystem Protection in a Sustainable World: A challange for Science and Regulation, Abstract Book.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Regulatory guidelines make heavy use of Concentration Addition (CA) as a tool for predicting and assessing the toxicity of chemical mixtures. CA assumes that the compounds in a mixture do not interact with each other, neither in their toxicokinetic nor in their toxicodynamic phase. However, several of those interactions are described in the scientific literature for almost all major groups of environmental chemicals. These result in essentially synergistic or antagonistic mixture toxicities, i.e. higher, respectively lower mixture toxicities than expected by CA. With a view on the regulatory risk assessment of chemical mixtures, it is hence important to quantify the range of expectable synergisms, respectively antagonisms. I discuss the quantitative consequences of interactions for the predictive power of CA using two published studies on the hazards and risks of environmentally realistic mixtures. One case study concerns the human health effects of a mixture of anti-androgens, the other the ecotoxicity of a pesticide mixture. Based on a series of simulation studies in which interactions were gradually assumed to occur in the mixtures, I outline the limiting cases (worst case situations) as well as the fundamental relationship between expectable deviations from CA and number of mixture components, mixture ratio and number of interacting substances in the mixture.
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| 7. |
- Franz, Jan, 1973, et al.
(författare)
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Molecule Formation by Radiative Association
- 2010
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Ingår i: The Chemical Cosmos: Understanding Chemistry in Astronomical Environments.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Franz, Jan, 1973, et al.
(författare)
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Molecule Formation in Interstellar Space
- 2010
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Ingår i: Department of Chemical- and Biological Engineering at Chalmers University of Technology and Chemistry at University of Gothenburg.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 9. |
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| 10. |
- Zhang, Rui, et al.
(författare)
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Positron collisions with molecular hydrogen: cross sections and annihilation parameters calculated using the R-matrix with pseudo-states method
- 2011
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Ingår i: J. Phys. B: At. Mol. Opt. Phys.. - 0953-4075 .- 1361-6455. ; 44:3
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Tidskriftsartikel (refereegranskat)abstract
- The molecular R-matrix with pseudo-states (MRMPS) method is employed to study positron collisions with H2. The calculations employ pseudo-continuum orbital sets containing up to h (l = 5) functions. Use of these high l functions is found to give converged eigenphase sums. Below the positronium formation threshold, the calculated cross sections agree with other high-accuracy theories and generally with the measurements. Calculation of the positron annihilation parameter Zeff with the MRMPS wavefunctions gives values significantly higher than other R-matrix wavefunctions but still do not completely converge with h functions. Extrapolation to higher l-values leads to a predicted value of Zeff for H2 of about 10.4. The MRMPS method is both completely general and ab initio; it can therefore be applied to positron collisions with other molecular targets.
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