Delayed Babcock-Leighton dynamos in the diffusion-dominated regime

Context. Solar dynamo models of Babcock-Leighton type typically assume the rise of magnetic flux tubes to be instantaneous. Solutions with high-magnetic-diffusivity have too short periods and a wrong migration of their active belts. Only the low-diffusivity regime with advective meridional flows is usually considered. Aims. In the present paper we discuss these assumptions and applied a time delay in the source term of the azimuthally averaged induction equation. This delay is set to be the rise time of magnetic flux tubes which supposedly form at the tachocline. We study the effect of the delay, which adds to the spacial non-locality a non-linear temporal one, in the advective but particularly in the diffusive regime. Methods. Fournier et al. (2017) obtained the rise time according to stellar parameters such as rotation, and the magnetic field strength at the bottom of the convection zone. These results allowed us to constrain the delay in the mean-field model used in a parameter study. Results. We identify an unknown family of solutions. These solutions self-quench, and exhibit longer periods than their non-delayed counterparts. Additionally, we demonstrate that the non-linear delay is responsible for the recover of the equatorward migration of the active belts at high turbulent diffusivities. Conclusions. By introducing a non-linear temporal non-locality (the delay) in a Babcock-Leighton dynamo model, we could obtain solutions quantitatively comparable to the solar butterfly diagram in the diffusion-dominated regime.Comment: 11 pages, 10 Figure

Experimental evolution induces loss of female-fertility in vitro in the fungal pathogen of rice, Magnaporthe oryzae

Sexual reproduction is widespread in eukaryotic organisms. Inmany fungal species previously known to reproduce asexually, some populations have been shown to encounter episodes of sexual reproduction. It has been suggested that mostfungi that are pathogenic on plants may reproduce sexually near their center of origin but have lost this ability during their dispersion. If a population reproduces exclusively clonally forseveral generations, individuals may accumulate deleterious mutations in loci controlling sexual reproduction. This may result in a complete loss of sexual reproduction ability. We tested this hypothesis on /Magnaporthe oryzae/, which is responsible for the most important fungal disease on cultivated rice worldwide: blast. In this species, only asexual spores are observed in the field. However, some strains coming from the putative center of origin of the fungus (in South East Asia, near the Himalayan Foothills) are able to produce viable sexual spores /in vitro/, and indirect evidence that sexual reproduction do occur /in natura/ in this region have been recently provided (see the abstract by E. Fournier).//In this heterothallic fungus,//sexual reproduction can occur only between two different strains of opposite mating type. Moreover, at least one of them, independently from the mating type, must be female-fertile, that is to be able to produce the sexual organs (perithecia) where meiosis takes place. We performed /in vitro /experimental evolution of four female-fertile strains for 10-20 "clonal generations". These strains came from a recombinant population of the center of origin. Each of the four strains became female-sterile in about 100 days in at least one of the two replicates we performed. This loss of female-fertility was accompanied by a reduction of asexual sporulation /in vitro /and /in planta/.//As epigenetical effects could explain the frequent loss of female-fertility observed, we tested if stress could restore it. Four different stresses were tested: extremely low temperature (-80°C), mycelium fragmentation by sonication, monosporic isolation, growth on plant. None of these stresses achieved to restore female-fertility, so the loss of female-fertility might be explained by genetical rather than epigenetical mechanisms. Crosses were performed between mutant strains that had lost female-fertility and wild type strains. In the offspring, the female-fertility phenotype segregated in 1:3 proportions. Backcrosses between F1 female-sterile strains and wild type strains gave the same result, supporting the hypothesis of a genetic control. Here we showed for the first time that female-fertility could be rapidly lost in theabsence of sexual reproduction in /M. oryzae/ strains from rice. We showed that it might be due to mutation accumulation, probably at several loci. From these results we hypothesize that sexual reproduction ability may have been lost rapidly during the dispersion of the disease from Asia to the rest of the world. More generally, this study provides a case study to test hypotheses on the enigma of sex. (Texte intégral

Pinsker estimators for local helioseismology

A major goal of helioseismology is the three-dimensional reconstruction of the three velocity components of convective flows in the solar interior from sets of wave travel-time measurements. For small amplitude flows, the forward problem is described in good approximation by a large system of convolution equations. The input observations are highly noisy random vectors with a known dense covariance matrix. This leads to a large statistical linear inverse problem. Whereas for deterministic linear inverse problems several computationally efficient minimax optimal regularization methods exist, only one minimax-optimal linear estimator exists for statistical linear inverse problems: the Pinsker estimator. However, it is often computationally inefficient because it requires a singular value decomposition of the forward operator or it is not applicable because of an unknown noise covariance matrix, so it is rarely used for real-world problems. These limitations do not apply in helioseismology. We present a simplified proof of the optimality properties of the Pinsker estimator and show that it yields significantly better reconstructions than traditional inversion methods used in helioseismology, i.e.\ Regularized Least Squares (Tikhonov regularization) and SOLA (approximate inverse) methods. Moreover, we discuss the incorporation of the mass conservation constraint in the Pinsker scheme using staggered grids. With this improvement we can reconstruct not only horizontal, but also vertical velocity components that are much smaller in amplitude

Field-dependent diamagnetic transition in magnetic superconductor Sm1.85Ce0.15CuO4−ySm_{1.85} Ce_{0.15} Cu O_{4-y}

The magnetic penetration depth of single crystal $\rm{Sm_{1.85}Ce_{0.15}CuO_{4-y}}$ was measured down to 0.4 K in dc fields up to 7 kOe. For insulating $\rm{Sm_2CuO_4}$, Sm$^{3+}$ spins order at the N\'{e}el temperature, $T_N = 6$ K, independent of the applied field. Superconducting $\rm{Sm_{1.85}Ce_{0.15}CuO_{4-y}}$ ($T_c \approx 23$ K) shows a sharp increase in diamagnetic screening below $T^{\ast}(H)$ which varied from 4.0 K ($H = 0$) to 0.5 K ($H =$ 7 kOe) for a field along the c-axis. If the field was aligned parallel to the conducting planes, $T^{\ast}$ remained unchanged. The unusual field dependence of $T^{\ast}$ indicates a spin freezing transition that dramatically increases the superfluid density.Comment: 4 pages, RevTex

Discrimination of the light CP-odd scalars between in the NMSSM and in the SLHM

The presence of the light CP-odd scalar boson predicted in the next-to-minimal supersymmetric model (NMSSM) and the simplest little Higgs model (SLHM) dramatically changes the phenomenology of the Higgs sector. We suggest a practical strategy to discriminate the underlying model of the CP-odd scalar boson produced in the decay of the standard model-like Higgs boson. We define the decay rate of "the non $b$-tagged jet pair" with which we compute the ratio of decay rates into lepton and jets. They show much different behaviors between the NMSSM and the SLHM.Comment: 5 pages, 2 figures (5 figure files

Alien Registration- Fournier, Rose D. (Lewiston, Androscoggin County)

https://digitalmaine.com/alien_docs/29751/thumbnail.jp

Alien Registration- Fournier, Elizabeth D. (Brunswick, Cumberland County)

https://digitalmaine.com/alien_docs/31474/thumbnail.jp

Alien Registration- Fournier, Fred D. (Van Buren, Aroostook County)

https://digitalmaine.com/alien_docs/33298/thumbnail.jp