15,496 research outputs found
Cyclic asymptotic behaviour of a population reproducing by fission into two equal parts
We study the asymptotic behaviour of the following linear
growth-fragmentation equation and prove that under fairly general assumptions on the division
rate its solution converges towards an oscillatory function,explicitely
given by the projection of the initial state on the space generated by the
countable set of the dominant eigenvectors of the operator. Despite the lack of
hypo-coercivity of the operator, the proof relies on a general relative entropy
argument in a convenient weighted space, where well-posedness is obtained
via semigroup analysis. We also propose a non-dissipative numerical scheme,
able to capture the oscillations
A 2D model for hydrodynamics and biology coupling applied to algae growth simulations
Cultivating oleaginous microalgae in specific culturing devices such as
raceways is seen as a future way to produce biofuel. The complexity of this
process coupling non linear biological activity to hydrodynamics makes the
optimization problem very delicate. The large amount of parameters to be taken
into account paves the way for a useful mathematical modeling. Due to the
heterogeneity of raceways along the depth dimension regarding temperature,
light intensity or nutrients availability, we adopt a multilayer approach for
hydrodynamics and biology. For free surface hydrodynamics, we use a multilayer
Saint-Venant model that allows mass exchanges, forced by a simplified
representation of the paddlewheel. Then, starting from an improved Droop model
that includes light effect on algae growth, we derive a similar multilayer
system for the biological part. A kinetic interpretation of the whole system
results in an efficient numerical scheme. We show through numerical simulations
in two dimensions that our approach is capable of discriminating between
situations of mixed water or calm and heterogeneous pond. Moreover, we exhibit
that a posteriori treatment of our velocity fields can provide lagrangian
trajectories which are of great interest to assess the actual light pattern
perceived by the algal cells and therefore understand its impact on the
photosynthesis process.Comment: 27 pages, 11 figure
Creep behaviour of as received, aged and cold worked INCONEL 617 at 850 °C and 950 °C
The effect of initial microstructure on alloy 617 creep behaviour has been investigated at 850 °C and 950 °C. The solution treated material shows non-classical creep behaviour at both temperatures with a strain rate drop at the beginning of the tests followed by a creep rate increase to a plateau before the onset of the tertiary creep. The intragranular secondary carbides which precipitate early at test temperature are responsible of the strong initial hardening effect by pinning the dislocations. This effect is overpassed during the thermo mechanical ageing of the alloy which induces growth of these carbides. Prior 1000 h thermal ageing at the temperature test totally removes the strain rate drop and reduces the lifetime. The intragranular microstructure has evolved thanks to the prior thermal ageing before the creep tests. Microstructural examinations also show the presence of grain boundary migration and recrystallization in the material during creep tests of the as received and aged materials. Preliminary cold work treatment highly reduces the strain rate of Inconel 617 and enhances the lifetime at 850 °C while the opposite is observed at 950 °C
Understanding interface effects in perovskite thin films
The control of matter properties (transport, magnetic, dielectric,...) using
synthesis as thin films is strongly hindered by the lack of reliable theories,
able to guide the design of new systems, through the understanding of the
interface effects and of the way the substrate constraints are imposed to the
material. The present paper analyses the energetic contributions at the
interfaces, and proposes a model describing the microscopic mechanisms
governing the interactions at an epitaxial interface between a manganite and
another transition metal oxide in perovskite structure (as for instance ). The model is checked against experimental results and literature
analysis
Layer-averaged Euler and Navier-Stokes equations
In this paper we propose a strategy to approximate incompressible hydrostatic
free surface Euler and Navier-Stokes models. The main advantage of the proposed
models is that the water depth is a dynamical variable of the system and hence
the model is formulated over a fixed domain.The proposed strategy extends
previous works approximating the Euler and Navier-Stokes systems using a
multilayer description. Here, the needed closure relations are obtained using
an energy-based optimality criterion instead of an asymptotic expansion.
Moreover, the layer-averaged description is successfully applied to the
Navier-Stokes system with a general form of the Cauchy stress tensor
An Analytical Expression for the Hubble diagram of supernovae and gamma-ray bursts
A recent paper by Harmut Traunm\"uller shows that the most adequate equation
to interpret the observations on magnitude and redshift from 892 type 1a
supernovae would be mu = 5 log[(1+z) ln(1+z)] + const. We discuss this result
which is exacly the one we have obtained few years ago when postulating a
relation between the speed of light and the expansion of the universe. We also
compare our analytical result to the conclusion of Marosi who studied 280
supernovae and gamma-ray bursts in the range 0.1014 < z < 8.1. The difference
between his results and ours is at worst of 0.3 %.Comment: 7 pages, 1 figur
Semantic and pragmatic motivations for constructional preferences: a corpus-based study of provide, supply, and present
A select group of transfer verbs can enter into four different constructions: the ditransitive construction (He provided John the money), the prepositional-dative construction (He provided the money to John), a construction with a prepositional theme (He provided John with the money), and a construction with a recipient realized by a for-phrase (He provided the money for John). In this article, we take a close look at three such verbs: provide, supply, and present. Corpus analysis shows that these three verbs display different structural preferences with respect to the for-, to-, and with-patterns. To explain these preferences, the study investigates pragmatic principles (following Mukherjee 2001 on provide) and the role played by semantic factors. An examination of the semantics of the verbs and the lexically motivated constructional semantics of the to, for, and with-patterns shows (i) that the three constructions are not interchangeable, and (ii) that the preferential differences between the three verbs find an explanation in the compatibility between lexical and constructional semantics. The description is mainly based on data from the British National Corpus
Tax Evasion and Social Interactions
The paper extends the standard tax evasion model by allowing for social interactions. In Manski's (1993) nomenclature, our model takes into account social conformity effects (i.e., endogenous interactions), fairness effects (i.e., exogenous interactions) and sorting effects (i.e., correlated effects). Our model is tested using experimental data. Participants must decide how much income to report given their tax rate and audit probability, and given those faced by the other members of their group as well as their mean reported income. The estimation is based on a two-limit simultaneous tobit with fixed group effects. A unique social equilibrium exists when the model satisfies coherency conditions. In line with Brock and Durlauf (2001b), the intrinsic nonlinearity between individual and group responses is sufficient to identify the model without imposing any exclusion restrictions. Our results are consistent with fairness effects but reject social conformity and correlated effects.social interactions; tax evasion; simultaneous tobit; laboratory experiments
Tax Evasion and Social Interactions
The paper extends the standard tax evasion model by allowing for social interactions. In Manski's (1993) nomenclature, our model takes into account social conformity effects (i.e., endogenous interactions), fairness effects (i.e., exogenous interactions) and sorting effects (i.e., correlated effects). Our model is tested using experimental data. Participants must decide how much income to report given their tax rate and audit probability, and given those faced by the other members of their group as well as their mean reported income. The estimation is based on a two-limit simultaneous tobit with fixed group effects. A unique social equilibrium exists when the model satisfies coherency conditions. In line with Brock and Durlauf (2001b), the intrinsic nonlinearity between individual and group responses is sufficient to identify the model without imposing any exclusion restrictions. Our results are consistent with fairness effects but reject social conformity and correlated effects.laboratory experiments; simultaneous Tobit; social interactions; tax evasion
Tax Evasion and Social Interactions
The paper extends the standard tax evasion model by allowing for social interactions. In Manski's (1993) nomenclature, our model takes into account social conformity effects (i.e., endogenous interactions), fairness effects (i.e., exogenous interactions) and sorting effects (i.e., correlated effects). Our model is tested using experimental data. Participants must decide how much income to report given their tax rate and audit probability, and given those faced by the other members of their group as well as their mean reported income. The estimation is based on a two-limit simultaneous tobit with fixed group effects. A unique social equilibrium exists when the model satisfies coherency conditions. In line with Brock and Durlauf (2001b), the intrinsic nonlinearity between individual and group responses is sufficient to identify the model without imposing any exclusion restrictions. Our results are consistent with fairness effects but reject social conformity and correlated effects.Social interactions, tax evasion, simultaneous tobit, laboratory experiments
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