Star formation history of Canis Major OB1 - II. A bimodal X-ray population revealed by XMM-Newton

The Canis Major OB1 Association has an intriguing scenario of star formation, especially in the Canis Major R1 (CMa R1) region traditionally assigned to a reflection nebula, but in reality an ionized region. This work is focused on the young stellar population associated to CMa R1, for which our previous results from ROSAT, optical and near-infrared data had revealed two stellar groups with different ages, suggesting a possible mixing of populations originated from distinct star-formation episodes. The X-ray data allow the detected sources to be characterized according to hardness ratios, light curves and spectra. Estimates of mass and age were obtained from the 2MASS catalogue, and used to define a complete subsample of stellar counterparts, for statistical purposes. A catalogue of 387 XMM-Newton sources is provided, 78% being confirmed as members or probable members of the CMa R1 association. Flares were observed for 13 sources, and the spectra of 21 bright sources could be fitted by a thermal plasma model. Mean values of fits parameters were used to estimate X-ray luminosities. We found a minimum value of log(L$_X$[erg/s]) = 29.43, indicating that our sample of low-mass stars (M$_\star$ $\leq$ 0.5 M$_\odot$), being faint X-ray emitters, is incomplete. Among the 250 objects selected as our complete subsample (defining our best sample), 171 are found to the East of the cloud, near Z CMa and dense molecular gas, 50% of them being young ( 10 Myr). The opposite happens to the West, near GU CMa, in areas lacking molecular gas: among 79 objects, 30% are young and 50% are older. These findings confirm that a first episode of distributed star formation occurred in the whole studied region ~10 Myr ago and dispersed the molecular gas, while a second, localized episode (< 5 Myr) took place in the regions where molecular gas is still present.Comment: 38 pages, 21 figures, accepted for A&

Slavnov-Taylor identities for noncommutative QED4_4

In this work we present an analysis of the one-loop Slavnov-Taylor identities in noncommutative QED$_4$. The vectorial fermion-photon and the triple photon vertex functions were studied, with the conclusion that no anomalies arise.Comment: 24 pages, revtex4, v2: typos correcte

Logarithmic behavior of degradation dynamics in metal--oxide semiconductor devices

In this paper the authors describe a theoretical simple statistical modelling of relaxation process in metal-oxide semiconductor devices that governs its degradation. Basically, starting from an initial state where a given number of traps are occupied, the dynamics of the relaxation process is measured calculating the density of occupied traps and its fluctuations (second moment) as function of time. Our theoretical results show a universal logarithmic law for the density of occupied traps $\bar{} \sim \phi (T,E_{F}) (A+B \ln t)$, i.e., the degradation is logarithmic and its amplitude depends on the temperature and Fermi Level of device. Our approach reduces the work to the averages determined by simple binomial sums that are corroborated by our Monte Carlo simulations and by experimental results from literature, which bear in mind enlightening elucidations about the physics of degradation of semiconductor devices of our modern life

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Carryover effect of fomesafen, applied on edible bean, on sucessional maize.

Em dois experimentos fomesafen foi aplicado em pós-emergência em culturas do feijoeiro nas doses de O; 0.125; 0.25; 0.375 e 0.5 kg/ha, em 1992 (abril e agosto) e em 1993 (março e agosto) em parcelas distintas, para avaliar os efeitos de seus resíduos no solo argiloso (Latossolo Vermelho-Escuro) na cultura do milho. O milho foi plantado em sucessão 65 e 198 dias após aplicação de fomesafen em 1992 e 65 e 2 12 dias em 1993. Resíduos de fomesafen no solo foram determinados por cromatografia líquida e foram detectados até 20 cm de profundidade, porém a maior concentração encontrada foi a 0-10 cm de profundidade. Nesta profundidade, a concentração de fomesafen variou de 21 a 24 e 55 a 60 ppb aos 2 I 2 e 65 dias após aplicação de 0,25 kg.ha-1 de fomesafen, respectivamente, enquanto que a aplicação de 0.5 kg.ha-1, apresentou concentrações de 46 a 61 e 137 a 193 ppb aos 212 e 65 dias após aplicação, respectivamente. No plantio de milho aos 65 dias após aplicação de fomesafen. resíduos do herbicida no solo reduziram o teor de clorofila na folha e volume de raiz do milho aos 10 dias após emergência. A diminuição do teor de clorofila na folha e volume de raiz, entretanto, não afetaram o rendimento de grãos