Effect of hot-water treatments on budburst and rooting of grapevine cuttings

Basal or apical parts of grapevine cuttings as well as entire cuttings were treated with hot water at a temperature of 50 °c for 30 min. Root initiation was delayed following HWT of entire cuttings and treatment of the basal parts only. HWT of the apical parts of cuttings resulted in a marked stimulating effect on time of sprouting, root initiation, mean number and mass of roots.Einfluß der Warmwasserbehandlung auf Austrieb und Wurzelbildung von RebenstecklingenDreiaugenstecklinge der Rebsorten Salt Creek (Ramsey) und Jacquez (mittleres und unteres Auge geblendet) wurden 30 min lang partiell oder gänzlich in 50 °c warmes Wasser getaucht. Wurden die ganzen Stecklinge oder der basale Pol behandelt, so war die Wurzelbildung gegenüber der Kontrolle verzögert. Durch Warmwasserbehandlung des apikalen Pols wurden dagegen der Austrieb und die Bewurzelung beträchtlich beschleunigt und die Anzahl und Masse der Wurzeln vermehrt

The bar-mode instability in differentially rotating neutron stars: Simulations in full general relativity

We study the dynamical stability against bar-mode deformation of rapidly spinning neutron stars with differential rotation. We perform fully relativistic 3D simulations of compact stars with $M/R \geq 0.1$, where $M$ is the total gravitational mass and $R$ the equatorial circumferential radius. We adopt an adiabatic equation of state with adiabatic index $\Gamma=2$. As in Newtonian theory, we find that stars above a critical value of $\beta \equiv T/W$ (where $T$ is the rotational kinetic energy and $W$ the gravitational binding energy) are dynamically unstable to bar formation. For our adopted choices of stellar compaction and rotation profile, the critical value of $\beta = \beta_{dGR}$ is $\sim 0.24-0.25$, only slightly smaller than the well-known Newtonian value $\sim 0.27$ for incompressible Maclaurin spheroids. The critical value depends only very weakly on the degree of differential rotation for the moderate range we surveyed. All unstable stars form bars on a dynamical timescale. Models with sufficiently large $\beta$ subsequently form spiral arms and eject mass, driving the remnant to a dynamically stable state. Models with moderately large $\beta \gtrsim \beta_{dGR}$ do not develop spiral arms or eject mass but adjust to form dynamically stable ellipsoidal-like configurations. If the bar-mode instability is triggered in supernovae collapse or binary neutron star mergers, it could be a strong and observable source of gravitational waves. We determine characteristic wave amplitudes and frequencies.Comment: 17 pages, accepted for publication in AP

Numerical approach for high precision 3-D relativistic star models

A multi-domain spectral method for computing very high precision 3-D stellar models is presented. The boundary of each domain is chosen in order to coincide with a physical discontinuity (e.g. the star's surface). In addition, a regularization procedure is introduced to deal with the infinite derivatives on the boundary that may appear in the density field when stiff equations of state are used. Consequently all the physical fields are smooth functions on each domain and the spectral method is absolutely free of any Gibbs phenomenon, which yields to a very high precision. The power of this method is demonstrated by direct comparison with analytical solutions such as MacLaurin spheroids and Roche ellipsoids. The relative numerical error reveals to be of the order of $10^{-10}$. This approach has been developed for the study of relativistic inspiralling binaries. It may be applied to a wider class of astrophysical problems such as the study of relativistic rotating stars too.Comment: Minor changes, Phys. Rev. D in pres

The ontogeny of somatic embryos from in vitro cultured grapevine anthers

CITATION: Newton, D. J. & Goussard, P. G.. 1990. The ontogeny of somatic embryos from in vitro cultured grapevine anthers. South African Journal of Enology & Viticulture, 11(2):70-75, doi:10.21548/11-2-2271.The original publication is available at http://www.journals.ac.za/index.php/sajevTranslucent light green to yellow anthers excised from Vitis rupestris cv. Rupestris du Lot flower buds, produced from cuttings grown in a climate-controlled room, produced somatic embryos when cultured on modified Nitsch & Nitsch (1969) medium supplemented with l μM 6-benzylaminopurine (BAP) and 5 μM 2,4-dichlorophenoxyacetic acid (2,4-D). Anatomical features of developing embryogenic explants were studied at various intervals, before and after the start of in vitro culture, using light microscopy. Results indicated that callus was entirely of somatic origin. Embryogenic cells were apparently present before in vitro culture commenced and multiplied sufficiently within the first 15 days' culture to form visible embryogenic growth centres. Embryogenic callus formed from the lateral and abaxial walls of the anther, all connective tissues and the filament. Somatic embryos were observed after 60 days of culture and possessed primordial vascular tissues and secondary embryoids. No vascular connections between somatic embryos were observed.http://www.journals.ac.za/index.php/sajev/article/view/2271Publisher's versio

The Magnetorotational Instability in Core Collapse Supernova Explosions

We investigate the action of the magnetorotational instability (MRI) in the context of iron-core collapse. Exponential growth of the field on the rotation time scale by the MRI will dominate the linear growth process of field line "wrapping" with the same characteristic time. We examine a variety of initial rotation states, with solid body rotation or a gradient in rotational velocity, that correspond to models in the literature. A relatively modest value of the initial rotation, a period of ~ 10 s, will give a very rapidly rotating PNS and hence strong differential rotation with respect to the infalling matter. We assume conservation of angular momentum on spherical shells. Results are discussed for two examples of saturation fields, a fiducial field that corresponds to Alfven velocity = rotational velocity and a field that corresponds to the maximum growing mode of the MRI. Modest initial rotation velocities of the iron core result in sub-Keplerian rotation and a sub-equipartition magnetic field that nevertheless produce substantial MHD luminosity and hoop stresses: saturation fields of order 10^{15} - 10^{16} G develop within 300 msec after bounce with an associated MHD luminosity of about 10^{52} erg/s. Bi-polar flows driven by this MHD power can affect or even cause the explosions associated with core-collapse supernovae.Comment: 42 pages, including 15 figures. Accepted for publication in ApJ. We have revised to include an improved treatment of the convection, and some figures have been update