Refining low-volume, high-concentration herbicide applications to control Chromolaena odorata (L.) King & Robinson (Siam weed) in remote areas

Chromolaena odorata (L.) King and Robinson (Siam weed) is a highly invasive plant and a high priority for control in north Queensland. It can be effectively treated using high-volume, groundbased herbicide spray equipment, but operational information shows that this control method becomes increasingly difficult in areas where vehicle access is prevented by rougher terrain. Low-volume, high-concentration herbicide applications have proven capable of causing high mortality in these remote situations. Two trials were undertaken between May 2010 and May 2012 to refine effective rates of aminopyralid/fluroxypyr, fluroxypyr and metsulfuron-methyl, only using low-volume, high-concentration applications on Siam weed. Fluroxypyr on its own was as effective as aminopyralid/fluroxypyr as both herbicides caused 95-100% mortality at overlapping rates containing 5 to 18.85 g a.i. L-1 of fluroxypyr. Metsulfuron-methyl caused 100% mortality when applied at 3 and 6 g a.i. L-1. Effective control was achieved with approximately 16 to 22 mL of the solutions per plant, so a 5 L mixture in a backpack could treat 170 to 310 adult plants. There are several options for treating Siam weed on the ground and the choice of methods reflects the area, plant density and accessibility of the infestation. Control information from Siam weed field crews shows that low volume, high concentration herbicide applications applied using a splatter gun are a more efficient method for controlling larger, denser remote infestations than physical removal. By identifying effective herbicides that are applied through low-volume equipment, these trials provide an additional and more efficient tool for controlling Siam weed in remote areas

Refining low-volume, high-concentration herbicide applications to control Chromolaena odorata (L.) King & Robinson (Siam weed) in remote areas

Chromolaena odorata (L.) King and Robinson (Siam weed) is a highly invasive plant and a high priority for control in north Queensland. It can be effectively treated using high-volume, groundbased herbicide spray equipment, but operational information shows that this control method becomes increasingly difficult in areas where vehicle access is prevented by rougher terrain. Low-volume, high-concentration herbicide applications have proven capable of causing high mortality in these remote situations. Two trials were undertaken between May 2010 and May 2012 to refine effective rates of aminopyralid/fluroxypyr, fluroxypyr and metsulfuron-methyl, only using low-volume, high-concentration applications on Siam weed. Fluroxypyr on its own was as effective as aminopyralid/fluroxypyr as both herbicides caused 95-100% mortality at overlapping rates containing 5 to 18.85 g a.i. L-1 of fluroxypyr. Metsulfuron-methyl caused 100% mortality when applied at 3 and 6 g a.i. L-1. Effective control was achieved with approximately 16 to 22 mL of the solutions per plant, so a 5 L mixture in a backpack could treat 170 to 310 adult plants. There are several options for treating Siam weed on the ground and the choice of methods reflects the area, plant density and accessibility of the infestation. Control information from Siam weed field crews shows that low volume, high concentration herbicide applications applied using a splatter gun are a more efficient method for controlling larger, denser remote infestations than physical removal. By identifying effective herbicides that are applied through low-volume equipment, these trials provide an additional and more efficient tool for controlling Siam weed in remote areas

Starquakes spring stellar surprises

Don Kurtz, Simon Jeffrey and Conny Aerts describe discoveries in the new era of precision asteroseismology. We call it the “Tychonic Principle”: a revolutionary improvement in observational precision inevitably leads to discovery. For Tycho Brahe, the improvement was in precision of astromet- ric position; for us, over the decades since we were students, it has been orders of magnitude improvement in the precision of radial velocity and photometric measure- ments for stars. Three decades ago, stellar radial velocities were measured to 1 kms–1 precision; now, in the best cases they are measured to 10s of cms–1. Three decades ago, stellar light variability was measured to mmag precision (one part per thousand); now in the best cases it is measured to better than µmag precision (one part per million). Stellar astrophysics is being revo- lutionized by this new ultra-high precision. The driving force has been the search for exoplanets. The two main techniques for exoplanet searches – radial velocity and transit measurements – require exquisite precision to detect either the tiny perturba- tive motion of a star being tugged about by a planet, or the slight drop in stellar bright- ness as a planet transits its star. The improvement in radial velocity preci- sion came about from brilliant engineering: 1 Luminosity– effective temperature (Hertzsprung–Russell) diagram showing locations of major pulsating variables coloured roughly by spectral type, the zero- age main sequence and horizontal branch, the Cepheid instability strip, and evolution tracks for model stars of various masses, indicated by small numbers (M⊙). Shadings represent heat-engine p modes (\\\), g modes (///) and strange modes (|||) and acoustically driven stochastic modes (≡). Rough spectral types are shown on the top axis. (Based on figures by J Christensen-Dalsgaard and then by CS Jeffery. See Jeffery & Saio 2016) of stellar apparent brightnesses – the µmag revolution – came with space missions that took photometers above the Earth’s atmos- phere. The highest precision ground-based photometry of one particular star reached 14 µmag – 14 parts per million (Kurtz et al. 2005) – in pulsation amplitude, but typically 1 mmag has been considered old photoelectric photometers, or dozens with CCDs on the ground. The third – and for some purposes the most important – benefit is the nearly continuous observa- tions for four years of about 150000 stars. For decades, groups of astronomers have organized campaigns to observe pulsating stars contemporaneously ground-based spectrographs have been placed in temperature-stabilized vacuums on vibrationally stable platforms with the light from the telescope fibre-fed to the ultra-stable spectrographs. For exoplanet good. With the advent of the French-led ESA CoRoT mis- sion and the NASA Kepler mission, it has become pos- sible to reach µmag precision “Stellar astrophysics is being revolutionized by this new ultra-high precision” from observatories around the world to try to get con- tinuous measurement of the changes in stellar brightness; one project for this is called searches the spectroscopic measurements have to provide true radial velocities to feed into Newton’s form of Kepler’s third law to determine the planets’ masses. This carries its own difficulties; at radial velocity preci- sion better than 1 ms–1 even the definition of radial velocity is interestingly complex (Lindegren & Dravins 2003). But, for astero- seismology, the fundamental data are the pulsation frequencies, with only secondary information coming from the amplitudes of the radial velocity excursions. The improvement in the measurement for thousands of stars simultaneously. The planet hunters have built beautifully stable spectrographs and ultra-precise photometers in their search for exoplanets; we asteroseismologists have used those precision data for new stellar astrophysics. Here, we are primarily showing results from the Kepler mission. For asteroseismol- ogy this mission provided multifold ben- efits over ground-based observations. The obvious one is the µmag precision; another is the observation of 200000 stars simulta- neously, instead of just one at a time with the “Whole Earth Telescope”, (WET; see Provencal et al. 2014). But where WET can observe a single target, or a few targets, for several weeks with duty cycles (fraction of time observing out of the full time possible) of, say, 50%, Kepler observations have bet- ter than 90% duty cycles for four years for 150000 stars. For many asteroseismic tar- gets this unprecedented length of observing time has been the key to discovery. So the planet hunters drove the technol- ogy development. We asteroseismologists have put that technology to excellent use. I

Convective quenching of stellar pulsations

Context: we study the convection-pulsation coupling that occurs in cold Cepheids close to the red edge of the classical instability strip. In these stars, the surface convective zone is supposed to stabilise the radial oscillations excited by the kappa-mechanism. Aims: we study the influence of the convective motions onto the amplitude and the nonlinear saturation of acoustic modes excited by kappa-mechanism. We are interested in determining the physical conditions needed to lead to a quenching of oscillations by convection. Methods: we compute two-dimensional nonlinear simulations (DNS) of the convection-pulsation coupling, in which the oscillations are sustained by a continuous physical process: the kappa-mechanism. Thanks to both a frequential analysis and a projection of the physical fields onto an acoustic subspace, we study how the convective motions affect the unstable radial oscillations. Results: depending on the initial physical conditions, two main behaviours are obtained: (i) either the unstable fundamental acoustic mode has a large amplitude, carries the bulk of the kinetic energy and shows a nonlinear saturation similar to the purely radiative case; (ii) or the convective motions affect significantly the mode amplitude that remains very weak. In this second case, convection is quenching the acoustic oscillations. We interpret these discrepancies in terms of the difference in density contrast: larger stratification leads to smaller convective plumes that do not affect much the purely radial modes, while large-scale vortices may quench the oscillations.Comment: 15 pages, 17 figures, 3 tables, accepted for publication in A&

Stories of hope

This is a narrative account, reflected from the author’s perspective, of three teachers’ resistance to the formulation of metrication and fabrication arising from the influence of STEM in science education. It focuses on the ways transformative science teaching challenges this obstacle viewed through the lens of Critical Realism and how social justice is meshed into science pedagogy

Orbital ordering in transition-metal compounds: I. The 120-degree model

We study the classical version of the 120-degree model. This is an attractive nearest-neighbor system in three dimensions with XY (rotor) spins and interaction such that only a particular projection of the spins gets coupled in each coordinate direction. Although the Hamiltonian has only discrete symmetries, it turns out that every constant field is a ground state. Employing a combination of spin-wave and contour arguments we establish the existence of long-range order at low temperatures. This suggests a mechanism for a type of ordering in certain models of transition-metal compounds where the very existence of long-range order has heretofore been a matter of some controversy.Comment: 40 pages, 1 eps fig; a revised version correcting a bunch of small error

Asteroseismic measurement of surface-to-core rotation in a main-sequence A star, KIC 11145123

We have discovered rotationally split core g-mode triplets and surface p-mode triplets and quintuplets in a terminal age main-sequence A star, KIC 11145123, that shows both δ Sct p-mode pulsations and γ Dor g-mode pulsations. This gives the first robust determination of the rotation of the deep core and surface of a main-sequence star, essentially model independently. We find its rotation to be nearly uniform with a period near 100 d, but we show with high confidence that the surface rotates slightly faster than the core. A strong angular momentum transfer mechanism must be operating to produce the nearly rigid rotation, and a mechanism other than viscosity must be operating toproduce a more rapidly rotating surface than core. Our asteroseismic result, along with previous asteroseismic constraints on internal rotation in some B stars, and measurements of internal rotation in some subgiant, giant and white dwarf stars,has made angular momentum transport in stars throughout their lifetimes an observational science

Asteroseismic measurement of slow, nearly uniform surface-to-core rotation in the main-sequence F star KIC 9244992

We have found a rotationally split series of core g-mode triplets and surface p-mode multiplets in a main-sequence F star, KIC 9244992. Comparison with models shows that the star has a mass of about 1.45 M�, and is at an advanced stage of main-sequence evolution in which the central hydrogen abundance mass fraction is reduced to about 0.1. This is the second case, following KIC 11145123, of an asteroseismic determination of the rotation of the deep core and surface of an A-F main-sequence star. We have found, essentially model independently, that the rotation near the surface, obtained from p-mode splittings, is 66 d, slightly slower than the rotation of 64 d in the core, measured by g-mode splittings. KIC 9244992 is similar to KIC 11145123 in that both are near the end of main-sequence stage with very slow and nearly uniform rotation. This indicates the angular momentum transport in the interior of an A-F star during the main-sequence stage is much stronger than that expected from standard theoretical formulations

Mesoscale flows in large aspect ratio simulations of turbulent compressible convection

We present the results of a very large aspect ratio (42.6) numerical simulation of fully compressible turbulent convection in a polytropic atmosphere, and focus on the properties of large-scale flows. Mesoscale patterns dominate the turbulent energy spectrum. We show that these structures, which had already been observed in Boussinesq simulations by Cattaneo et al. (2001), have a genuine convective origin and do not result directly from collective interactions of the smaller scales of the flow, even though their growth is strongly affected by nonlinear transfers. If this result is relevant to the solar photosphere, it suggests that the dominant convective mode below the Sun's surface may be at mesoscales.Comment: 5 pages, 7 figures (reduced quality) -- published in A&A in 2005 but not uploaded to the arxi