Looking for activity cycles in late-type Kepler stars using time-frequency analysis

We analyse light curves covering four years of 39 fast-rotating ($P_\mathrm{rot}< 1d$) late-type active stars from the Kepler database. Using time-frequency analysis (Short-Term Fourier-Transform), we find hints for activity cycles of 300-900 days at 9 targets from the changing typical latitude of the starspots, which, with the differential rotation of the stellar surface change the observed rotation period over the activity cycle. We also give a lowest estimation for the shear parameter of the differential rotation, which is ~0.001 for the cycling targets. These results populate the less studied, short period end of the rotation-cycle length relation.Comment: 12 pages, 7 figures, accepted for publication in MNRA

The use of activated charcoal in grapevine tissue cultures

The microporous structure, the extremely large inner surface associated with adsorptive capacity and evidence of positive effects of activated charcoal (AC) in plant tissue culture media were published in several reviews (Pan and van Staden, 1998, Thomas 2008, Ahmadian et al. 2013). However a detailed overview on its application for grapevine is still lacking. In this review we present a comprehensive scale of results about the application of AC in different areas of grapevine tissue culture such as micropropagation, embryo rescue, somatic embryogenesis, gene transfer, protoplast culture, cryopreservation, viroid and virus elimination. These summarized data of positive results are aimed at stimulating a more extensive and effective use of AC as a powerful and beneficial component of grapevine tissue culture media

Erratum

Thidiazuron-induced regeneration and genetic transformation of grapevine rootstock varietiesVitis 42 (3), 133- 136 (2003

Thidiazuron-induced regeneration and genetic transformation of grapevine rootstock varieties

In vitro regeneration from cell to plant, a technique considered to be an important precondition of gene transfer, was attempted in 12 grapevine rootstocks starting with anthers of the plants as inocula. Embryogenic callus was induced in solid Murashige-Skoog medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) and thidiazuron (TDZ). Five of the tested rootstock cultivars (Börner, Richter 110, SO 4, St. George and Teleki 5 C) yielded embryogenic callus lines that regenerated entire plants. From these cultures Richter 110 and St. George varieties produced transgenic plants following Agrobacterium-mediated transformation with an nptII/gusA gene construct using a simple, but effective cocultivation protocol. The putative transgenic lines expressed the gusA gene. The T-DNA transfer and integration was confirmed by PCR analysis.

Temporal walk based centrality metric for graph streams

Abstract A plethora of centrality measures or rankings have been proposed to account for the importance of the nodes of a network. In the seminal study of Boldi and Vigna (2014), the comparative evaluation of centrality measures was termed a difficult, arduous task. In networks with fast dynamics, such as the Twitter mention or retweet graphs, predicting emerging centrality is even more challenging. Our main result is a new, temporal walk based dynamic centrality measure that models temporal information propagation by considering the order of edge creation. Dynamic centrality measures have already started to emerge in publications; however, their empirical evaluation is limited. One of our main contributions is creating a quantitative experiment to assess temporal centrality metrics. In this experiment, our new measure outperforms graph snapshot based static and other recently proposed dynamic centrality measures in assigning the highest time-aware centrality to the actually relevant nodes of the network. Additional experiments over different data sets show that our method perform well for detecting concept drift in the process that generates the graphs

Investigating magnetic activity in very stable stellar magnetic fields: long-term photometric and spectroscopic study of the fully convective M4 dwarf V374 Peg

The ultrafast-rotating ($P_\mathrm{rot}\approx0.44 d$) fully convective single M4 dwarf V374 Peg is a well-known laboratory for studying intense stellar activity in a stable magnetic topology. As an observable proxy for the stellar magnetic field, we study the stability of the light curve, and thus the spot configuration. We also measure the occurrence rate of flares and coronal mass ejections (CMEs). We analyse spectroscopic observations, $BV(RI)_C$ photometry covering 5 years, and additional $R_C$ photometry that expands the temporal base over 16 years. The light curve suggests an almost rigid-body rotation, and a spot configuration that is stable over about 16 years, confirming the previous indications of a very stable magnetic field. We observed small changes on a nightly timescale, and frequent flaring, including a possible sympathetic flare. The strongest flares seem to be more concentrated around the phase where the light curve indicates a smaller active region. Spectral data suggest a complex CME with falling-back and re-ejected material, with a maximal projected velocity of $\approx$675km/s. We observed a CME rate much lower than expected from extrapolations of the solar flare-CME relation to active stars.Comment: 15 figures, 4 tables, accepted for publication in A&

M-Dwarf Fast Rotators and the Detection of Relatively Young Multiple M-Star Systems

We have searched the Kepler light curves of ~3900 M-star targets for evidence of periodicities that indicate, by means of the effects of starspots, rapid stellar rotation. Several analysis techniques, including Fourier transforms, inspection of folded light curves, 'sonograms', and phase tracking of individual modulation cycles, were applied in order to distinguish the periodicities due to rapid rotation from those due to stellar pulsations, eclipsing binaries, or transiting planets. We find 178 Kepler M-star targets with rotation periods, P_rot, of < 2 days, and 110 with P_rot < 1 day. Some 30 of the 178 systems exhibit two or more independent short periods within the same Kepler photometric aperture, while several have three or more short periods. Adaptive optics imaging and modeling of the Kepler pixel response function for a subset of our sample support the conclusion that the targets with multiple periods are highly likely to be relatively young physical binary, triple, and even quadruple M star systems. We explore in detail the one object with four incommensurate periods all less than 1.2 days, and show that two of the periods arise from one of a close pair of stars, while the other two arise from the second star, which itself is probably a visual binary. If most of these M-star systems with multiple periods turn out to be bound M stars, this could prove a valuable way of discovering young hierarchical M-star systems; the same approach may also be applicable to G and K stars. The ~5% occurrence rate of rapid rotation among the ~3900 M star targets is consistent with spin evolution models that include an initial contraction phase followed by magnetic braking, wherein a typical M star can spend several hundred Myr before spinning down to periods longer than 2 days.Comment: 17 pages, 12 figures, 2 tables; accepted for publication in The Astrophysical Journa

Evaluation of intron containing potential reference gene-specific primers to validate grapevine nucleic acid samples prepared for conventional PCR and RT-PCR

Previously we proved the usefulness of an intron containing reference gene, phosphoenolpyruvate carboxylase (PEP) to validate cDNA synthesis for detection of grapevine viruses by conventional RT-PCR from crude nucleic acid preparations. Thus amplicons derived from residual genomic DNA (gDNA) and cDNA can be clearly distinguished by their sizes. Here we designed novel sets of primers which encompass one or two intron containing sequences of grapevine housekeeping genes such as actin, tubulin and elongation factor 1-α. Using these primers the expected sequences were amplified from gDNAs of the tested 24 grapevine cultivars. Thereafter they were challenged using cDNAs prepared from total nucleic acid samples isolated from cambial scrapings of dormant canes, leaf laminas, petioles and in vitro leaves of 12 grapevine cultivars. All of these novel, and the previously published PEP gene-specific primers generated the amplification of the expected shorter DNA fragments without introns. Thus they are suitable to check the quality of nucleic acid preparations and to validate subsequent cDNA synthesis prior to pathogen detection assays