The effect of competition on the control of invading plant pathogens

1. New invading pathogen strains must compete with endemic pathogen strains to emerge and spread. As disease control measures are often non-specific, i.e. they do not distinguish between strains, applying control not only affects the invading pathogen strain but the endemic as well. We hypothesise that the control of the invasive strain could be compromised due to the non-specific nature of the control. 2. A spatially-explicit model, describing the East African cassava mosaic virus-Uganda strain (EACMV-UG) outbreak, is used to evaluate methods of controlling both disease incidence and spread of invading pathogen strains in pathosystems with and without an endemic pathogen strain present. 3. We find that while many newly introduced or intensified control measures (such as resistant cultivars or roguing) decrease the expected incidence, they have the unintended consequence of increasing, or at least not reducing, the speed with which the invasive pathogen spreads geographically. We identify which controls cause this effect and methods in which these controls may be applied to prevent it. 4. We found that the spatial spread of the invading strain is chiefly governed by the incidence at the wave front. Control can therefore be applied, or intensified, once the wave front has passed without increasing the pathogen’s rate of spread. 5. When trade of planting material occurs, it is possible that the planting material is already infected. The only forms of control in this study that reduces the speed of geographic spread, regardless of the presence of an endemic strain, are those that reduce the amount of trade and the distance over which trade takes place. 6. Synthesis and applications. Imposing trade restrictions before the epidemic has reached a given area and increasing other control methods only once the wave front has passed is the most effective way of both slowing down spread and controlling incidence when the presence of an endemic strain is unknow

Voltage imaging of waking mouse cortex reveals emergence of critical neuronal dynamics.

Complex cognitive processes require neuronal activity to be coordinated across multiple scales, ranging from local microcircuits to cortex-wide networks. However, multiscale cortical dynamics are not well understood because few experimental approaches have provided sufficient support for hypotheses involving multiscale interactions. To address these limitations, we used, in experiments involving mice, genetically encoded voltage indicator imaging, which measures cortex-wide electrical activity at high spatiotemporal resolution. Here we show that, as mice recovered from anesthesia, scale-invariant spatiotemporal patterns of neuronal activity gradually emerge. We show for the first time that this scale-invariant activity spans four orders of magnitude in awake mice. In contrast, we found that the cortical dynamics of anesthetized mice were not scale invariant. Our results bridge empirical evidence from disparate scales and support theoretical predictions that the awake cortex operates in a dynamical regime known as criticality. The criticality hypothesis predicts that small-scale cortical dynamics are governed by the same principles as those governing larger-scale dynamics. Importantly, these scale-invariant principles also optimize certain aspects of information processing. Our results suggest that during the emergence from anesthesia, criticality arises as information processing demands increase. We expect that, as measurement tools advance toward larger scales and greater resolution, the multiscale framework offered by criticality will continue to provide quantitative predictions and insight on how neurons, microcircuits, and large-scale networks are dynamically coordinated in the brain

Anisotropic Distribution of SDSS Satellite Galaxies: Planar (not Polar) Alignment

The distribution of satellite galaxies relative to isolated host galaxies in the Sloan Digital Sky Survey (SDSS) is investigated. Host-satellite systems are selected using three different methods, yielding samples of ~3300, ~1600, and \~950 satellites. In the plane of the sky, the distributions of all three samples show highly significant deviations from circular symmetry (> 99.99%, > 99.99%, and 99.79% confidence levels, respectively), and the degree of anisotropy is a strong function of the projected radius, r_p, at which the satellites are found. For r_p < 100 kpc, the SDSS satellites are aligned preferentially with the major axes of the hosts. This is in stark contrast to the Holmberg effect, in which satellites are aligned with the minor axes of host galaxies. The degree of anisotropy in the distribution of the SDSS satellites decreases with r_p and is consistent with an isotropic distribution at of order the 1-sigma level for 250 kpc < r_p < 500 kpc.Comment: ApJ Letters (in press); Discussion section substantially revised, SDSS DR3 included in the analysis, no significant changes to the result

Performance of AAOmega: the AAT multi-purpose fibre-fed spectrograph

AAOmega is the new spectrograph for the 2dF fibre-positioning system on the Anglo-Australian Telescope. It is a bench-mounted, double-beamed design, using volume phase holographic (VPH) gratings and articulating cameras. It is fed by 392 fibres from either of the two 2dF field plates, or by the 512 fibre SPIRAL integral field unit (IFU) at Cassegrain focus. Wavelength coverage is 370 to 950nm and spectral resolution 1,000-8,000 in multi-Object mode, or 1,500-10,000 in IFU mode. Multi-object mode was commissioned in January 2006 and the IFU system will be commissioned in June 2006. The spectrograph is located off the telescope in a thermally isolated room and the 2dF fibres have been replaced by new 38m broadband fibres. Despite the increased fibre length, we have achieved a large increase in throughput by use of VPH gratings, more efficient coatings and new detectors - amounting to a factor of at least 2 in the red. The number of spectral resolution elements and the maximum resolution are both more than doubled, and the stability is an order of magnitude better. The spectrograph comprises: an f/3.15 Schmidt collimator, incorporating a dichroic beam-splitter; interchangeable VPH gratings; and articulating red and blue f/1.3 Schmidt cameras. Pupil size is 190mm, determined by the competing demands of cost, obstruction losses, and maximum resolution. A full suite of VPH gratings has been provided to cover resolutions 1,000 to 7,500, and up to 10,000 at particular wavelengths.Comment: 13 pages, 4 figures; presented at SPIE, Astronomical Telescopes and Instrumentation, 24 - 31 May 2006, Orlando, Florida US

Sequence structure emission in The Red Rectangle Bands

We report high resolution (R~37,000) integral field spectroscopy of the central region (r<14arcsec) of the Red Rectangle nebula surrounding HD44179. The observations focus on the 5800A emission feature, the bluest of the yellow/red emission bands in the Red Rectangle. We propose that the emission feature, widely believed to be a molecular emission band, is not a molecular rotation contour, but a vibrational contour caused by overlapping sequence bands from a molecule with an extended chromophore. We model the feature as arising in a Polycyclic Aromatic Hydrocarbon (PAH) with 45-100 carbon atoms.Comment: 13 pages, 9 figures, accepted for publication in ApJ. A version of the paper with full resolution figures is available at: http://www.aao.gov.au/local/www/rgs/Sequence-Structure

Recent changes in area and thickness of Torngat Mountain glaciers (northern Labrador, Canada)

The Torngat Mountains National Park, northern Labrador, Canada, contains more than 120 small glaciers: the only remaining glaciers in continental northeast North America. These small cirque glaciers exist in a unique topo-climatic setting, experiencing temperate maritime summer conditions yet very cold and dry winters, and may provide insights into the deglaciation dynamics of similar small glaciers in temperate mountain settings. Due to their size and remote location, very little information exists regarding the health of these glaciers. Just a single study has been published on the contemporary glaciology of the Torngat Mountains, focusing on net mass balances from 1981 to 1984. This paper addresses the extent to which glaciologically relevant climate variables have changed in northern Labrador in concert with 20th-century Arctic warming, and how these changes have affected Torngat Mountain glaciers. Field surveys and remote-sensing analyses were used to measure regional glacier area loss of 27 % from 1950 to 2005, substantial rates of ice surface thinning (up to 6 m yr−1) and volume losses at Abraham, Hidden, and Minaret glaciers, between 2005 and 2011. Glacier mass balances appear to be controlled by variations in winter precipitation and, increasingly, by strong summer and autumn atmospheric warming since the early 1990s, though further observations are required to fully understand mass balance sensitivities. This study provides the first comprehensive contemporary assessment of Labrador glaciers and will inform both regional impact assessments and syntheses of global glacier mass balance