(Borel) convergence of the variationally improved mass expansion and the O(N) Gross-Neveu model mass gap

We reconsider in some detail a construction allowing (Borel) convergence of an alternative perturbative expansion, for specific physical quantities of asymptotically free models. The usual perturbative expansions (with an explicit mass dependence) are transmuted into expansions in 1/F, where $F \sim 1/g(m)$ for $m \gg \Lambda$ while $F \sim (m/\Lambda)^\alpha$ for m \lsim \Lambda, $\Lambda$ being the basic scale and $\alpha$ given by renormalization group coefficients. (Borel) convergence holds in a range of $F$ which corresponds to reach unambiguously the strong coupling infrared regime near $m\to 0$, which can define certain "non-perturbative" quantities, such as the mass gap, from a resummation of this alternative expansion. Convergence properties can be further improved, when combined with $\delta$ expansion (variationally improved perturbation) methods. We illustrate these results by re-evaluating, from purely perturbative informations, the O(N) Gross-Neveu model mass gap, known for arbitrary $N$ from exact S matrix results. Comparing different levels of approximations that can be defined within our framework, we find reasonable agreement with the exact result.Comment: 33 pp., RevTeX4, 6 eps figures. Minor typos, notation and wording corrections, 2 references added. To appear in Phys. Rev.

Bone Morphogenetic Protein-6 (BMP-6) induces atresia in goat primordial follicles cultured in vitro

This study investigated the effects of bone morphogenetic protein 6 (BMP-6) on in vitro primordial follicle development in goats. Samples of goat ovarian cortex were cultured in vitro for 1 or 7 days in Minimum Essential Medium (control medium) supplemented with different concentrations of BMP-6. Follicle survival, activation and growth were evaluated through histology and transmission electron microscopy (TEM). After 7 days of culture, histological analysis demonstrated that BMP-6 enhanced the percentages of atretic primordial follicles when compared to fresh control (day 0). Nevertheless, BMP-6 increased follicular and oocyte diameter during both culture periods. As the culture period progressed from day 1 to day 7, a significant increase in follicle diameter was observed with 1 or 50ng/ml BMP-6. However, on the contrary to that observed with the control medium TEM revealed that follicles cultured for up to 7 days with 1 or 50ng/ml BMP-6 had evident signs of atresia. In conclusion, this study demonstrated that BMP-6 negatively affects the survival and ultrastructure of goat primordial follicles.O presente estudo investigou os efeitos da proteína morfogenética óssea-6 (BMP-6) no desenvolvimento in vitro de folículos primordiais caprinos. Amostras de córtex ovariano de cabras foram cultivados por 1 ou 7 dias em Meio Essencial Mínimo (meio controle) suplementado com diferentes concentrações de BMP-6. As taxas de sobrevivência, ativação e crescimento foram avaliadas por histologia clássica e microscopia eletrônica de transmissão (MET). Após 7 dias de cultivo, a análise histológica demonstrou que a BMP-6 aumentou o percentual de folículos primordiais degenerados no dia 7 quando comparados ao controle fresco (D0). Além disso, houve um aumento significativo do diâmetro folicular e oocitário em ambos os períodos de cultivo em todos os tratamentos na presença de BMP-6. Com a progressão do cultivo do dia 1 para o dia 7, nos tratamentos com 1 ou 50ng/ml de BMP-6, foi observado um aumento significativo no diâmetro folicular. Entretanto, contrário ao observado no meio controle, a MET revelou que os folículos cultivados nesses tratamentos apresentavam sinais evidentes de atresia. Em conclusão, esse estudo demonstrou que a BMP-6 afeta negativamente a sobrevivência e a ultra-estrutura de folículos primordiais caprinos

Constraining the wind launching region in Herbig Ae stars: AMBER/VLTI spectroscopy of HD 104237

Astronomy and Astrophysics, 464, pp. 55-58, http://dx.doi.org./10.1051/0004-6361:20065719International audienc