1,795 research outputs found
How Planting Density Affects Number and Yield of Potato Minitubers in a Commercial Glasshouse Production System
Commercial potato minituber production systems aim at high tuber numbers per plant. This study investigated by which mechanisms planting density (25.0, 62.5 and 145.8 plants/m2) of in vitro derived plantlets affected minituber yield and minituber number per plantlet. Lowering planting density resulted in a slower increase in soil cover by the leaves and reduced the accumulated intercepted radiation (AIR). It initially also reduced light use efficiency (LUE) and harvest index, and thus tuber weights per m2. At the commercial harvest 10 weeks after planting (WAP), LUE tended to be higher at lower densities. This compensated for the lower AIR and led to only slightly lower tuber yields. Lowering planting density increased tuber numbers per (planted) plantlet in all grades. It improved plantlet survival and increased stem numbers per plant. However, fewer stolons were produced per stem, whereas stolon numbers per plant were not affected. At lower densities, more tubers were initiated per stolon and the balance between initiation and later resorption of tubers was more favourable. Early interplant competition was thought to reduce the number of tubers initiated at higher densities, whereas later-occurring interplant competition resulted in a large fraction of the initiated tubers being resorbed at intermediate planting densities. At low planting densities, the high number of tubers initiated was also retained. Shortening of the production period could be considered at higher planting densities, because tuber number in the commercial grade > 9 mm did not increase any more after 6 WA
Detection, Localization and Characterization of Gravitational Wave Bursts in a Pulsar Timing Array
Efforts to detect gravitational waves by timing an array of pulsars have
focused traditionally on stationary gravitational waves: e.g., stochastic or
periodic signals. Gravitational wave bursts --- signals whose duration is much
shorter than the observation period --- will also arise in the pulsar timing
array waveband. Sources that give rise to detectable bursts include the
formation or coalescence of supermassive black holes (SMBHs), the periapsis
passage of compact objects in highly elliptic or unbound orbits about a SMBH,
or cusps on cosmic strings. Here we describe how pulsar timing array data may
be analyzed to detect and characterize these bursts. Our analysis addresses, in
a mutually consistent manner, a hierarchy of three questions: \emph{i}) What
are the odds that a dataset includes the signal from a gravitational wave
burst? \emph{ii}) Assuming the presence of a burst, what is the direction to
its source? and \emph{iii}) Assuming the burst propagation direction, what is
the burst waveform's time dependence in each of its polarization states?
Applying our analysis to synthetic data sets we find that we can \emph{detect}
gravitational waves even when the radiation is too weak to either localize the
source of infer the waveform, and \emph{detect} and \emph{localize} sources
even when the radiation amplitude is too weak to permit the waveform to be
determined. While the context of our discussion is gravitational wave detection
via pulsar timing arrays, the analysis itself is directly applicable to
gravitational wave detection using either ground or space-based detector data.Comment: 43 pages, 13 figures, submitted to ApJ
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