56Ni dredge-up in Supernova 1987A

We use early-time observations of He I 10830 \AA to measure the extent of upward mixing of radioactive material in SN 1987A. This work develops and extends the work of Graham (1988), and places constraints on actual explosion models. The presence of the He I 10830 \AA (2s^{3}S--2p^{3}P) line at $\geq 10$ days post-explosion implies re-ionisation by $\gamma$-rays from upwardly-mixed radioactive material produced during the explosion. Using the unmixed explosion model 10H (Woosley 1988) as well as mixed versions of it, we estimated the $\gamma$-ray energy deposition by applying a purely absorptive radiative transfer calculation. The deposition energy was used to find the ionisation balance as a function of radius, and hence the 2s$^{3}$S population density profile. This was then applied to a spectral synthesis model and the synthetic spectra were compared with the observations. Neither model 10H nor the mixed version, 10HMM, succeeded in reproducing the observed He I 10830 \AA line. The discrepancy with the data found for 10HMM is particularly significant, as this model has successfully reproduced the X-ray and $\gamma$-ray observations and the UVOIR light curve. We find that a match to the He I line profile is achieved by reducing the extent of mixing in 10HMM. Our reduced-mixing models also reproduce the observed $\gamma$-ray line light curves and the iron-group velocities deduced from late-time infrared line profiles. We suggest that the He I line method provides a more sensitive measure of the extent of mixing in a type II supernova explosion.Comment: 18 pages, 5 figures, accepted for publication in MNRAS (uses epsf.sty - included

Early-time Spitzer observations of the type II-Plateau supernova, 2004dj

We present mid-infrared observations with the Spitzer Space Telescope of the nearby type II-P supernova, SN 2004dj, at epochs of 89 to 129 days. We have obtained the first mid-IR spectra of any supernova apart from SN 1987A. A prominent [NiII] 6.64 micron line is observed, from which we deduce that the mass of stable nickel must be at least 2.2e10(-4) Msun. We also observe the red wing of the CO-fundamental band. We relate our findings to possible progenitors and favour an evolved star, most likely a red supergiant, with a probable initial mass between ~10 and 15 Msun.Comment: ApJ Letters (accepted

Spectroscopically Peculiar Type Ia Supernovae and Implications for Progenitors

In a recent paper Li et al. (2000) reported that 36 percent of 45 Type Ia supernovae (SNe Ia) discovered since 1997 in two volume-limited supernova searches were spectroscopically peculiar, and they suggested that because this peculiarity rate is higher than that reported for an earlier observational sample by Branch et al. (1993), it is now more likely that SNe Ia are produced by more than one kind of progenitor. In this paper I discuss and clarify the differences between the results of Li et al. and Branch et al. and I suggest that multiple progenitor systems are now less likely than they were before.Comment: 11 pages; accepted by PASP; several minor changes, 2 references added, main conclusions unchange

Cross Border Community Research, Opportunities and Challenges: Case Study Analyses

In the context of a global knowledge economy, this paper underscores the need for cross border social and community research and suggests several critical procedures necessary for successful implementation of such research projects. Using data derived from diverse sources it describes the importance of cross border knowledge sharing, and critical procedures that enlarge the perimeter of traditional teaching and learning experiences. It further describes the advantages of implementing a combination of in-class instruction and field-based activities in international settings. A discussion of the constraints and benefits of conducting social and community-based fieldwork in politically stable developing countries follows

On the High--Velocity Ejecta of the Type Ia Supernova 1994D

Synthetic spectra generated with the parameterized supernova synthetic-spectrum code SYNOW are compared to spectra of the Type Ia SN 1994D that were obtained before the time of maximum brightness. Evidence is found for the presence of two-component Fe II and Ca II features, forming in high velocity ($\ge 20,000$ \kms) and lower velocity ($\le 16,000$ \kms) matter. Possible interpretations of these spectral splits, and implications for using early--time spectra of SNe Ia to probe the metallicity of the progenitor white dwarf and the nature of the nuclear burning front in the outer layers of the explosion, are discussed.Comment: 15 pages, 3 figures, 3 tables, Astrophysical Journal, in pres

Heritability of testosterone levels in 12-year-old twins and its relation to pubertal development

The aim of this study was to estimate the heritability of variation in testosterone levels in 12-year-old children, and to explore the overlap in genetic and environmental influences on circulating testosterone levels and androgen dependent pubertal development. Midday salivary testosterone samples were collected on two consecutive days in a sample of 183 unselected twin pairs. Androgen induced pubertal development was assessed using self report Tanner scales of pubic hair development (boys and girls) and genital development (boys). A significant contribution of genetic effects to the variance in testosterone levels was found. Heritability was approximately 50% in both boys and girls. The remaining proportion of the variance in testosterone levels could be explained by non-shared environmental influences. The relatively high correlation between testosterone levels of opposite sex dizygotic twins suggests that sex differences in genes influencing variation in testosterone levels have not yet developed in pre- and early puberty. Variance in pubertal development was explained by a large genetic component, moderate shared environmental influences, and a small non-shared environmental effect. Testosterone levels correlated moderately (r = .31) with pubertal development; the covariance between testosterone levels and pubertal development was entirely accounted for by genetic influences

Plasma ACTH, α-MSH and cortisol variations in the dog during the oestrous cycle in different photoperiods

The hypothalamic-pituitary-adrenal axis (HPA) is a complex system regulated by multiple factors.Sexual dimorphism of this axis has been described in different species under physiological conditions and it hasbeen proposed that sexual hormones could have an effect on it. There are only a few reports about sex-linkedvariations in HPA axis hormones in the dog. Thus, studying the impact of sexual hormones on the HPA axis wouldbroaden the knowledge about its function in this species. Therefore, the objective of this study was to determinewhether there are variations in HPA plasma hormones (ACTH, alfa-melanocyte-stimulating hormone [α-MSH]and cortisol) according to the sex and photoperiod (positive or negative photoperiod were considered when theduration of the light hours of the day was more than 12 or less than 12, respectively) under basal conditions (likeanoestrus) and throughout the oestrous cycle in the female dog. The population under study consisted of 11 intactfemale and 14 intact male dogs. Under basal conditions neither ACTH nor α-MSH concentrations showed differencesbetween sexes and different photoperiods. Cortisol showed greater values in the negative photoperiod thanin the positive, both in females and males (P = 0.03 and P = 0.015, respectively). Throughout the oestrous cycle,all the studied hormones showed variations (P < 0.0001). The greatest concentrations of ACTH were observed atproestrus, while α-MSH and cortisol showed their greatest concentrations at oestrus. The three hormones decreasedin diestrus. ACTH and cortisol concentrations were higher in the negative photoperiod (P = 0.04 and P < 0.0001,respectively), while α-MSH concentrations were higher in the positive photoperiod (P = 0.012). In the group offemales oestradiol and progesterone correlated with ACTH (r = 0.75, P < 0.0001; r = 0.34, P < 0.01, respectively),α-MSH (r = 0.49, P < 0.0001; r = 0.52, P < 0.0001, respectively) and cortisol (r = 0.33, P < 0.01; r = 0.5, P < 0.0001,respectively). These results show that in females, HPA axis hormones vary during the oestrous cycle in relation tooestradiol and progesterone fluctuations. The ACTH, α-MSH and cortisol concentrations also showed differencesbetween photoperiods in females, but only cortisol did so in males. These findings suggest that sexual hormonescould have an effect on the HPA axis. Further research needs to be done to fully understand this interaction andthe mechanisms involved.Fil: Gallelli, María Florencia. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias; ArgentinaFil: Monachesi, N.. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias; ArgentinaFil: Miceli, Diego Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias; ArgentinaFil: Cabrera Battler, M. F.. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias; ArgentinaFil: Gomez, N. V.. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias; ArgentinaFil: Meikle, A.. Universidad de Montevideo; UruguayFil: Castillo, V, A.. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias; Argentin