Evaluating White Clover for Resistance to Cylindrocladium Root Rot

A rapid screening technique was developed for use in evaluating white clover (Trifolium repens L.) for resistance to Cylindrocladium root rot incited by Cylindrocladium crotalariae. Culture plates of the fungus were evaluated for number of infective propagules after four weeks of growth on potato dextrose agar, and no differences were detected among plates. Seedlings of ‘Osceola’ white clover were exposed in the greenhouse to four levels of inoculum over a six-week period, with resistance based on percent survival of uninoculated controls. It was shown that suspending 1 culture plate in 100ml of water and rating plants four weeks after inoculation was suitable for screening seedlings. A field test was conducted to verify greenhouse results. Results indicated that the greenhouse technique gave similar results, and would be sufficient to use in a breeding program to develop resistance to this disease

Selection of morphological traits to improve forage characteristics of Setaria sphacelata grown in Florida.

A genetically diverse population of Setaria sphacelata was developed at Gainesville, Florida by intercrossing the cultivars ?Narok?, ?Kazungula? and ?Solander? and a local persistent population. To determine heritability of traits that may improve setaria as a forage plant in Florida, progeny of the intercrossed population underwent two cycles of selection for inflorescence number and one cycle for leaf width. The selected populations, together with cultivars and introductions, were evaluated for morphological characters, yield and forage quality in field experiments with close- and wide-spaced plants. Increase of inflorescence number was not obtained by selection but resulted in decreased plant height, inflorescence length, yield, leaf width, and leafiness. Leaf width was increased by selection and was associated with increased leafiness and whole-plant crude protein content. The results suggest good prospects for selection of setaria cultivars suited to Florida with improved yield and quality providing they tolerate winter cold and reliably produce seed

A Comprehensive Comparative Test of Seven Widely-Used Spectral Synthesis Models Against Multi-Band Photometry of Young Massive Star Clusters

We test the predictions of spectral synthesis models based on seven different massive-star prescriptions against Legacy ExtraGalactic UV Survey (LEGUS) observations of eight young massive clusters in two local galaxies, NGC 1566 and NGC 5253, chosen because predictions of all seven models are available at the published galactic metallicities. The high angular resolution, extensive cluster inventory and full near-ultraviolet to near-infrared photometric coverage make the LEGUS dataset excellent for this study. We account for both stellar and nebular emission in the models and try two different prescriptions for attenuation by dust. From Bayesian fits of model libraries to the observations, we find remarkably low dispersion in the median E(B-V) (~0.03 mag), stellar masses (~10^4 M_\odot) and ages (~1 Myr) derived for individual clusters using different models, although maximum discrepancies in these quantities can reach 0.09 mag and factors of 2.8 and 2.5, respectively. This is for ranges in median properties of 0.05-0.54 mag, 1.8-10x10^4 M_\odot and 1.6-40 Myr spanned by the clusters in our sample. In terms of best fit, the observations are slightly better reproduced by models with interacting binaries and least well reproduced by models with single rotating stars. Our study provides a first quantitative estimate of the accuracies and uncertainties of the most recent spectral synthesis models of young stellar populations, demonstrates the good progress of models in fitting high-quality observations, and highlights the needs for a larger cluster sample and more extensive tests of the model parameter space.Comment: Accepted for publication in MNRAS (14 Jan. 2016). 30 pages, 16 figures, 9 table

Oxidation resistance of graphene-coated Cu and Cu/Ni alloy

The ability to protect refined metals from reactive environments is vital to many industrial and academic applications. Current solutions, however, typically introduce several negative effects, including increased thickness and changes in the metal physical properties. In this paper, we demonstrate for the first time the ability of graphene films grown by chemical vapor deposition to protect the surface of the metallic growth substrates of Cu and Cu/Ni alloy from air oxidation. SEM, Raman spectroscopy, and XPS studies show that the metal surface is well protected from oxidation even after heating at 200 \degree C in air for up to 4 hours. Our work further shows that graphene provides effective resistance against hydrogen peroxide. This protection method offers significant advantages and can be used on any metal that catalyzes graphene growth

Candidate LBV stars in galaxy NGC 7793 found via HST photometry + MUSE spectroscopy

Only about 19 Galactic and 25 extragalactic bonafide luminous blue variables (LBVs) are known to date. This incomplete census prevents our understanding of this crucial phase of massive star evolution which leads to the formation of heavy binary black holes via the classical channel. With large samples of LBVs one could better determine the duration and maximum stellar luminosity which characterize this phase. We search for candidate LBVs (cLBVs) in a new galaxy, NGC 7793. For this purpose, we combine high spatial resolution images from two Hubble Space Telescope (HST) programs with optical spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE). By combining PSF-fitting photometry measured on F547M, F657N, and F814W images, with restrictions on point-like appearance (at HST resolution) and H α luminosity, we find 100 potential cLBVs, 36 of which fall in the MUSE fields. Five of the latter 36 sources are promising cLBVs which have MV ≤ −7 and a combination of: H α with a P-Cygni profile; no [O I]λ6300 emission; weak or no [O III]λ5007 emission; large [N II]/H α relative to H II regions; and [S II]λ6716/[S II]λ6731∼1⁠. It is not clear if these five cLBVs are isolated from O-type stars, which would favour the binary formation scenario of LBVs. Our study, which approximately covers one fourth of the optical disc of NGC 7793, demonstrates how by combining the above HST surveys with multi-object spectroscopy from 8-m class telescopes, one can efficiently find large samples of cLBVs in nearby galaxies

Spectroscopic and evolutionary analyses of the binary system AzV 14 outline paths toward the WR stage at low metallicity

The origin of the observed population of Wolf-Rayet (WR) stars in low-metallicity (low-Z) galaxies, such as the Small Magellanic Cloud (SMC), is not yet understood. Standard, single-star evolutionary models predict that WR stars should stem from very massive O-type star progenitors, but these are very rare. On the other hand, binary evolutionary models predict that WR stars could originate from primary stars in close binaries. We conduct an analysis of the massive O star, AzV 14, to spectroscopically determine its fundamental and stellar wind parameters, which are then used to investigate evolutionary paths from the O-type to the WR stage with stellar evolutionary models. Multi-epoch UV and optical spectra of AzV 14 are analyzed using the non-LTE stellar atmosphere code PoWR. An optical TESS light curve was extracted and analyzed using the PHOEBE code. The obtained parameters are put into an evolutionary context, using the MESA code. AzV 14 is a close binary system consisting of two similar main sequence stars with masses of 32 Msol. Both stars have weak stellar winds with mass-loss rates of log $\dot{M}$ = -7.7. Binary evolutionary models can explain the empirically derived stellar and orbital parameters. The model predicts that the primary will evolve into a WR star with T = 100 kK, while the secondary, which will accrete significant amounts of mass during the first mass transfer phase, will become a cooler WR star with T = 50 kK and are predicted to have compared to other WR stars increased oxygen abundances. This model prediction is supported by a spectroscopic analysis of a WR star in the SMC. We hypothesize that the populations of WR stars in low-Z galaxies may have bimodal temperature distributions. Hotter WR stars might originate from primary stars, while cooler WR stars are the evolutionary descendants of the secondary stars if they accreted a significant amount of mass.Comment: 21 pages (13 main body + 8 appendix), 16 figures, 9 table

First narrow-band search for continuous gravitational waves from known pulsars in advanced detector data

Spinning neutron stars asymmetric with respect to their rotation axis are potential sources of continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a fully coherent search, based on matched filtering, which uses the position and rotational parameters obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signalto- noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch between the assumed and the true signal parameters. For this reason, narrow-band analysis methods have been developed, allowing a fully coherent search for gravitational waves from known pulsars over a fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of 11 pulsars using data from Advanced LIGO’s first observing run. Although we have found several initial outliers, further studies show no significant evidence for the presence of a gravitational wave signal. Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of the 11 targets over the bands searched; in the case of J1813-1749 the spin-down limit has been beaten for the first time. For an additional 3 targets, the median upper limit across the search bands is below the spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried out so far