A new EUVE-detected flare star (EUVE J0613-23.9B)

Extreme Ultraviolet Explorer (EUVE) observations have provided detailed spectroscopic and timing studies of several flare stars, including AU Mic (Cully et al., 1993), AD Leo (Hawley et al., 1995) and EQ Peg (Monsignori-Fossi et al., 1995). In this bulletin, we present the EUVE and optical follow-up observations of a newly detected flare star. This star was serendipitously discovered during an EUVE observation of the G star HD 43162 as part of the analysis for the 3rd EUVE Right Angle Program Catalog (Christian, 2002). Analysis of the EUVE spectra obtained during the largest flare (Fe XIX-XXIV emission and a strong 300-650 Å continuum) have been presented elsewhere (Christian et al., 2003). We present optical spectroscopy and results obtained at MT Stromlo Observatory to identify the optical counterpart in § 1, and the long-term EUVE Deep Survey light-curves in § 2

The influence of gibberellic acid and paclobutrazol on induction of somatic embryogenesis in wild type and hairy root cultures of Centaurium erythraea Gillib.

The effects of exogenous gibberellic acid (GA3) and paclobutrazol on induction of somatic embryos in wild type and hairy root culture of Centaurium erythraea Gillib. were investigated. Both compoundswere incorperated into 1/2 MS medium at 6 concentrations (0.01, 0.03, 0.1, 0.3, 1.0 and 3.0 ìM). Wild type root and hairy root explants cultured in the presence of GA3 at all tested concentrations under 16-h photoperiod or in the darkness decreased the number of somatic embryos that were produced. Paclobutrazol (0.3 mM) induced the largest number (19.7, 16.5) of somatic embryos in wild type and hairy root cultures, respectively. Rooting of plants derived from somatic embryos as achieved on ½MSmedium. These results indicate that paclobutrazol is beneficial for somatic embryo induction and formation in wild type and hairy root culture

Analiza mehaničkih svojstava F75 Co-Cr legure za primjenu kod selektivnog laserskog topljenja (SLT) izrade djelomičnih zubnih proteza

The presented work discusses the applicability of the selective laser melting technique (SLM) in manufacture of removable partial denture (RPD) frameworks with the emphasis on material properties. The paper presents initial results of a conducted test of the mechanical properties of the F75 Co-Cr dental alloy used with selective laser melting.Dana istraživanja se odnose na primjenljivost tehnike selektivnog laserskog topljenja (SLT) u proizvodnji djelomičnih zubnih proteza, pri čemu je posebna pažnja usmjerena na svojstva materijala. Rad prikazuje inicijalne rezultate sprovedenog testiranja mehaničkih svojstva F75 Co-Cr dentalne legure za primjenu kod selektivnog laserskog topljenja

Very Low Mass Stars and Brown Dwarfs in Taurus-Auriga

We present high resolution optical spectra obtained with the HIRES spectrograph on the Keck I telescope of low mass T Tauri stars and brown dwarfs (LMTTs) in Taurus-Auriga. Of particular interest is the previously classified "continuum T Tauri star" GM Tau, which has a spectral type of M6.5 and a mass just below the stellar/substellar boundary. None of the LMTTs in Taurus are rapidly rotating (vsini < 30 km/s), unlike low mass objects in Orion. Many of the slowly rotating, non-accreting stars and brown dwarfs exhibit prominent H-alpha emission (EWs of 3 - 36 A), indicative of active chromospheres. We demonstrate empirically that the full-width at 10% of the H-alpha emission profile peak is a more practical and possibly more accurate indicator of accretion than either the equivalent width of H-alpha or optical veiling: 10%-widths > 270 km/s are classical T Tauri stars (i.e. accreting), independent of stellar spectral type. Although LMTTs can have accretion rates comparable to that of more typical, higher-mass T Tauri stars (e.g. K7-M0), the average mass accretion rate appears to decrease with decreasing mass. The diminished frequency of accretion disks for LMTTs, in conjunction with their lower, on average, mass accretion rates, implies that they are formed with less massive disks than higher-mass T Tauri stars. The radial velocities, circumstellar properties and known binaries do not support the suggestion that many of the lowest mass members of Taurus have been ejected from higher stellar density regions within the cloud. Instead, LMTTs appear to have formed and are evolving in the same way as higher-mass T Tauri stars, but with smaller disks and shorter disk lifetimes.Comment: 27 pages, plus 8 figures, accepted for publication in Ap

On the Determination of N and O Abundances in Low Metallicity Systems

We show that in order to minimize the uncertainties in the N and O abundances of low mass, low metallicity (O/H less than or equal to solar/5) emission-line galaxies, it is necessary to employ separate parameterizations for inferring Te[N II] and Te[O II] from Te[O III]. In addition, we show that for the above systems, the ionization correction factor (ICF) for obtaining N/O from N+/O+, where the latter is derived from optical emission-line flux ratios, is = 1.08 +/- 0.09. These findings are based on state-of-the-art single-star H II region simulations, employing our own modeled stellar spectra as input. Our models offer the advantage of having matching stellar and nebular abundances. In addition, they have O/H as low as solar/50 (lower than any past work), as well as log(N/O) and log(C/O) fixed at characteristic values of -1.46 and -0.7, respectively. The above results were used to re-derive N and O abundances for a sample of 68 systems with 12 + log(O/H) less than or equal to 8.1, whose de-reddened emission-line strengths were collected from the literature. The analysis of the log(N/O) versus 12 + log(O/H) diagram of the above systems shows the following: (1) the largest group of objects forms the well-known N/O plateau with a value for the mean (and its statistical error) of -1.43 (+.0084/-.0085); (2) the objects are distributed within a range in log(N/O) of -1.54 to -1.27 in Gaussian fashion around the mean with a standard deviation of sigma = +.071 / -.084; and (3) a chi-square analysis suggests that only a small amount of the observed scatter in log(N/O) is intrinsic.Comment: 15 pages, 13 figures, 6 tables, accepted for publication in Ap

Linked MRI signatures of the brain\u27s acute and persistent response to concussion in female varsity rugby players

Acute brain changes are expected after concussion, yet there is growing evidence of persistent abnormalities well beyond clinical recovery and clearance to return to play. Multiparametric MRI is a powerful approach to non-invasively study structure-function relationships in the brain, however it remains challenging to interpret the complex and heterogeneous cascade of brain changes that manifest after concussion. Emerging conjunctive, data-driven analysis approaches like linked independent component analysis can integrate structural and functional imaging data to produce linked components that describe the shared inter-subject variance across images. These linked components not only offer the potential of a more comprehensive understanding of the underlying neurobiology of concussion, but can also provide reliable information at the level of an individual athlete. In this study, we analyzed resting-state functional MRI (rs-fMRI) and diffusion tensor imaging (DTI) within a cohort of female varsity rugby players (n = 52) through the in-and off-season, including concussed athletes (n = 21) who were studied longitudinally at three days, three months and six months after a diagnosed concussion. Linked components representing co-varying white matter microstructure and functional network connectivity characterized (a) the brain\u27s acute response to concussion and (b) persistent alterations beyond clinical recovery. Furthermore, we demonstrate that these long-term brain changes related to specific aspects of a concussion history and allowed us to monitor individual athletes before and longitudinally after a diagnosed concussion

Analysis and modeling of high temporal resolution spectroscopic observations of flares on AD Leo

We report the results of a high temporal resolution spectroscopic monitoring of the flare star AD Leo. During 4 nights, more than 600 spectra were taken in the optical range using the Isaac Newton Telescope (INT) and the Intermediate Dispersion Spectrograph (IDS). We have observed a large number of short and weak flares occurring very frequently (flare activity > 0.71 hours-1). This is in favour of the very important role that flares can play in stellar coronal heating. The detected flares are non white-light flares and, though most of solar flares belong to this kind, very few such events had been previously observed on stars. The behaviour of different chromospheric lines (Balmer series from H_alpha to H_11, Ca II H & K, Na I D_1 & D_2, He I 4026 AA and He I D_3) has been studied in detail for a total of 14 flares. We have also estimated the physical parameters of the flaring plasma by using a procedure which assumes a simplified slab model of flares. All the obtained physical parameters are consistent with previously derived values for stellar flares, and the areas - less than 2.3% of the stellar surface - are comparable with the size inferred for other solar and stellar flares. Finally, we have studied the relationships between the physical parameters and the area, duration, maximum flux and energy released during the detected flares.Comment: Latex file with 17 pages, 11 figures. Available at http://www.ucm.es/info/Astrof/invest/actividad/actividad_pub.html Accepted for publication in: Astronomy & Astrophysics (A&A