260 research outputs found
Fronts and interfaces in bistable extended mappings
We study the interfaces' time evolution in one-dimensional bistable extended
dynamical systems with discrete time. The dynamics is governed by the
competition between a local piece-wise affine bistable mapping and any
couplings given by the convolution with a function of bounded variation. We
prove the existence of travelling wave interfaces, namely fronts, and the
uniqueness of the corresponding selected velocity and shape. This selected
velocity is shown to be the propagating velocity for any interface, to depend
continuously on the couplings and to increase with the symmetry parameter of
the local nonlinearity. We apply the results to several examples including
discrete and continuous couplings, and the planar fronts' dynamics in
multi-dimensional Coupled Map Lattices. We eventually emphasize on the
extension to other kinds of fronts and to a more general class of bistable
extended mappings for which the couplings are allowed to be nonlinear and the
local map to be smooth.Comment: 27 pages, 3 figures, submitted to Nonlinearit
Optimization of control parameters of a hot cold controller by means of Simplex type methods
This paper describes a hot/cold controller for regulating crystallization
operations. The system was identified with a common method (the Broida method) and the parameters were obtained by the Ziegler-Nichols method. The paper shows that this empirical method will only allow a qualitative approach to regulation and that, in some instances, the parameters obtained are unreliable and therefore cannot be used to cancel variations between the set point and the actual values. Optimization methods were used to
determine the regulation parameters and solve this identcation problem. It was found that the weighted centroid method was the best one
Oxidative phosphorylation flexibility in the liver of mice resistant to high-fat diet-induced hepatic steatosis.
OBJECTIVE To identify metabolic pathways that may underlie susceptibility or resistance to high-fat diet-induced hepatic steatosis. RESEARCH DESIGN AND METHODS We performed comparative transcriptomic analysis of the livers of A/J and C57Bl/6 mice, which are, respectively, resistant and susceptible to high-fat diet-induced hepatosteatosis and obesity. Mice from both strains were fed a normal chow or a high-fat diet for 2, 10, and 30 days, and transcriptomic data were analyzed by time-dependent gene set enrichment analysis. Biochemical analysis of mitochondrial respiration was performed to confirm the transcriptomic analysis. RESULTS Time-dependent gene set enrichment analysis revealed a rapid, transient, and coordinate upregulation of 13 oxidative phosphorylation genes after initiation of high-fat diet feeding in the A/J, but not in the C57Bl/6, mouse livers. Biochemical analysis using liver mitochondria from both strains of mice confirmed a rapid increase by high-fat diet feeding of the respiration rate in A/J but not C57Bl/6 mice. Importantly, ATP production was the same in both types of mitochondria, indicating increased uncoupling of the A/J mitochondria. CONCLUSIONS Together with previous data showing increased expression of mitochondrial ÎČ-oxidation genes in C57Bl/6 but not A/J mouse livers, our present study suggests that an important aspect of the adaptation of livers to high-fat diet feeding is to increase the activity of the oxidative phosphorylation chain and its uncoupling to dissipate the excess of incoming metabolic energy and to reduce the production of reactive oxygen species. The flexibility in oxidative phosphorylation activity may thus participate in the protection of A/J mouse livers against the initial damages induced by high-fat diet feeding that may lead to hepatosteatosis
Oscillation of linear ordinary differential equations: on a theorem by A. Grigoriev
We give a simplified proof and an improvement of a recent theorem by A.
Grigoriev, placing an upper bound for the number of roots of linear
combinations of solutions to systems of linear equations with polynomial or
rational coefficients.Comment: 16 page
Close to Uniform Prime Number Generation With Fewer Random Bits
In this paper, we analyze several variants of a simple method for generating
prime numbers with fewer random bits. To generate a prime less than ,
the basic idea is to fix a constant , pick a
uniformly random coprime to , and choose of the form ,
where only is updated if the primality test fails. We prove that variants
of this approach provide prime generation algorithms requiring few random bits
and whose output distribution is close to uniform, under less and less
expensive assumptions: first a relatively strong conjecture by H.L. Montgomery,
made precise by Friedlander and Granville; then the Extended Riemann
Hypothesis; and finally fully unconditionally using the
Barban-Davenport-Halberstam theorem. We argue that this approach has a number
of desirable properties compared to previous algorithms.Comment: Full version of ICALP 2014 paper. Alternate version of IACR ePrint
Report 2011/48
Sharpenings of Li's criterion for the Riemann Hypothesis
Exact and asymptotic formulae are displayed for the coefficients
used in Li's criterion for the Riemann Hypothesis. For we obtain
that if (and only if) the Hypothesis is true,
(with and explicitly given, also for the case of more general zeta or
-functions); whereas in the opposite case, has a non-tempered
oscillatory form.Comment: 10 pages, Math. Phys. Anal. Geom (2006, at press). V2: minor text
corrections and updated reference
FFAT motif phosphorylation controls formation and lipid transfer function of interâorganelle contacts
Organelles are physically connected in membrane contact sites. The endoplasmic reticulum possesses three major receptors, VAPâA, VAPâB, and MOSPD2, which interact with proteins at the surface of other organelles to build contacts. VAPâA, VAPâB, and MOSPD2 contain an MSP domain, which binds a motif named FFAT (two phenylalanines in an acidic tract). In this study, we identified a nonâconventional FFAT motif where a conserved acidic residue is replaced by a serine/threonine. We show that phosphorylation of this serine/threonine is critical for nonâconventional FFAT motifs (named PhosphoâFFAT) to be recognized by the MSP domain. Moreover, structural analyses of the MSP domain alone or in complex with conventional and PhosphoâFFAT peptides revealed new mechanisms of interaction. Based on these new insights, we produced a novel prediction algorithm, which expands the repertoire of candidate proteins with a PhosphoâFFAT that are able to create membrane contact sites. Using a prototypical tethering complex made by STARD3 and VAP, we showed that phosphorylation is instrumental for the formation of ERâendosome contacts, and their sterol transfer function. This study reveals that phosphorylation acts as a general switch for interâorganelle contacts
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