ALBERT

Description: Cereal infection by the broad host range fungal pathogen Fusarium graminearum is a significant global agricultural and food safety issue due to the deposition of mycotoxins within infected grains. Methods to study the intracellular effects of mycotoxins often use the baker's yeast model system ( Saccharomyces cerevisiae ); however, this organism has an efficient drug export network known as the pleiotropic drug resistance (PDR) network, which consists of a family of multidrug exporters. This study describes the first study that has evaluated the potential involvement of all known or putative ATP-binding cassette (ABC) transporters from the PDR network in exporting the F. graminearum trichothecene mycotoxins deoxynivalenol (DON) and 15-acetyl-deoxynivalenol (15A-DON) from living yeast cells. We found that Pdr5p appears to be the only transporter from the PDR network capable of exporting these mycotoxins. We engineered mutants of Pdr5p at two sites previously identified as important in determining substrate specificity and inhibitor susceptibility. These results indicate that it is possible to alter inhibitor insensitivity while maintaining the ability of Pdr5p to export the mycotoxins DON and 15A-DON, which may enable the development of resistance strategies to generate more Fusarium -tolerant crop plants. Fusarium mycotoxins are efficiently exported from yeast cells by the multidrug resistance exporter Pdr5p. This ATP-binding cassette transporter can be modified to resist inhibition by both FK506 and enniatin B which suggests it may be possible to use this to engineer Fusarium resistance in plants.

Description: Ionospheric disturbances observed by bottom-side soundings of the ionosphere appear at many temporal and spatial scales. Australia has many simultaneous observations from vertically orientated ionospheric sounders with spatial separations on the scale of 1000 km. However, with this spatial sampling only large scale ionospheric disturbances can be mapped and subsequently modeled. DSTO has an experimental program in progress to investigate the smaller spatial scale disturbances. These are often seen on vertical incidence soundings and are uncorrelated with soundings from greater than 500 km away. They can also be uncorrelated with soundings from the same site only 15 min later. The DSTO program to investigate these ionospheric disturbances is called SpICE, for Spatial Ionospheric Correlation Experiment. SpICE uses a small set of transmitters and receivers with varying separations to achieve a geographically spread set of near-vertical incidence ionospheric “reflection” points separated by 50–150 km, allowing us to probe disturbances at this spatial scale. Using the latest digital receiver technology we can collect amplitude and phase information from the ionospheric returns of the continuous wave transmissions of a nearby transmitter that is rapidly sweeping through the HF band. The returned signal is processed at a very high resolution to achieve good signal-to-noise complex ionograms at better than one-minute time updates. To date there have been three SpICE campaigns. This paper will discuss the SpICE program goals and highlight some of the unusual features observed in the first campaign. Following papers will look more closely at this data set and the subsequent campaigns.

Description: [1]  DSTO has initiated an experimental programme, SpICE (Spatial Ionospheric Correlation Experiment), utilising state-of-the-art DSTO designed high frequency (HF) digital receivers. This programme seeks to understand ionospheric disturbances at scales 〈 150 km and temporal resolutions under 1 minute through the simultaneous observation and recording of multiple quasi-vertical ionograms (QVI) with closely spaced ionospheric control points. A detailed description of and results from the first campaign conducted in February 2008 were presented by [13]. In this paper we employ a 3D magneto-ionic Hamiltonian ray tracing engine (PHaRLAP), developed by DSTO, to (1) model the various disturbance features observed on both the O and X polarization modes in our QVI data and (2) understand how they are produced. The ionospheric disturbances which produce the observed features were modelled by perturbing the ionosphere with atmospheric gravity waves.

Description: The Jindalee Over-the-horizon Radar Network (JORN) is an integral part of Australia's national defence capability. JORN uses a real-time ionospheric model as part of its operations. The primary source of data for this model is a set of 13 vertical-incidence sounders (VIS) scattered around the Australian coast and inland locations. These sounders are a mix of Lowell DPS-1 and DPS-4. Both of these sounders, the DPS-1 in particular, are near the end of their maintainable life. A replacement for these aging sounders was required as part of the ongoing sustainment program for JORN. Over the last few years the High-Frequency Radar Branch (HFRB) of the Defence Science and Technology (DST) Group, Australian Department of Defence, has been developing its own sounders based on its successful radar hardware technology. The DST Group VIS solution known as PRIME (Portable Remote Ionospheric Monitoring Equipment) is a 100% duty-cycle, continuous-wave (CW) system that receives the returned ionospheric signal while it is still transmitting, and operates the receiver in the near-field of the transmitter. Of considerable importance to a successful VIS is the autoscaling software, which takes the ionogram data and produces an ionogram trace (group delay as a function of frequency), and from that produces a set of ionospheric parameters that represents the (bottomside) overhead electron density profile. HFRB has developed its own robust autoscaling software. The performance of DST Group's PRIME under a multitude of challenging ionospheric conditions has been studied. In December 2014, PRIME was trialled at a JORN VIS site collocated with the existing Lowell Digisonde DPS-1. This side-by-side testing determined that PRIME was fit-for-purpose. A summary of the results of this comparison and example PRIME output will be discussed. Note that this paper compares PRIME with the 25 year old Lowell Digisonde DPS-1, which is planned to be replaced. Our future plans include PRIME comparisons with the much newer Digisonde DPS-4D located at Learmonth in Western Australia.

Description: Inferring species interactions from co-occurrence data is one of the most controversial tasks in community ecology. One difficulty is that a single pairwise Interaction can ripple through an ecological network and produce surprising indirect consequences. For example, the negative correlation between two competing species can be reversed in the presence of a third species that outcompetes both of them. Here, I apply models from statistical physics, called Markov networks or Markov random fields, that can predict the direct and indirect consequences of any possible species interaction matrix. Interactions in these models can be estimated from observed co-occurrence rates via maximum likelihood, controlling for indirect effects. Using simulated landscapes with known interactions, I evaluated Markov networks and six existing approaches. Markov networks consistently outperformed the other methods, correctly isolating direct interactions between species pairs even when indirect interactions or abiotic factors largely overpowered them. Two computationally efficient approximations, which controlled for indirect effects with partial correlations or generalized linear models, also performed well. Null models showed no evidence of being able to control for indirect effects, and reliably yielded incorrect inferences when such effects were present. This article is protected by copyright. All rights reserved.

Description: From July to October 2015, the Australian Defence Science and Technology Group (DST Group) conducted an experiment during which a vertical incidence sounder (VIS) was set up at Alice Springs Airport. During September 2015 this VIS observed the passage of many large-scale traveling ionospheric disturbances (TIDs). By plotting the measured virtual heights across multiple frequencies as a function of time, the passage of the TID can be clearly displayed. Using this plotting method we show that all the TIDs observed during the campaign by the VIS at Alice Springs show an apparent downward phase progression of the crests and troughs. The passage of the TID can be more clearly interpreted by plotting the true height of iso-ionic contours across multiple plasma frequencies; the true heights can be obtained by inverting each ionogram to obtain an electron density profile. These plots can be used to measure the vertical phase speed of a TID, and also reveal a time lag between events seen in true height compared to virtual height. To the best of our knowledge this style of analysis has not previously been applied to other swept-frequency sounder observations. We develop a simple model to investigate the effect of the passage of a large-scale TID on a VIS. The model confirms that for a TID with a downward vertical phase progression, the crests and troughs will appear earlier in virtual height than in true height, and will have a smaller apparent speed in true height than in virtual height.

Description: The oblique-incidence sounder (OIS) is a well-established instrument for determining the state of the ionosphere, with several advantages over vertical-incidence sounders (VIS). However, the processing and interpretation of OIS ionograms is more complicated than that of VIS ionograms. Due to the Earth's magnetic field, the ionosphere is birefringent at radio frequencies and a VIS or OIS will typically see two distinct ionospheric returns, known as the O - and X -modes. The separation of these two modes on a VIS, using a polarimetric receive antenna, is a well-established technique. However, this process is more complicated on an OIS due to a variable phase separation in the phase difference between the two modes, as measured between the two arms of a polarimetric antenna. Using a polarimetric antenna that can be rotated and tilted, we show that this variation in phase separation within an ionogram is caused by the variation in incidence angle, with some configurations leading to greater variation in phase separation. We then develop an algorithm for separating O - and X -modes in oblique ionograms which can account for the variation in phase separation and we demonstrate successful separation even in relatively difficult cases. The variation in phase separation can also be exploited to estimate the incident elevation, a technique which may be useful for other applications of HF radio.

Description: The sounding of the ionosphere by a vertical-incidence sounder (VIS) is the oldest and most common technique for determining the state of the ionosphere. The automatic extraction of relevant ionospheric parameters from the ionogram image, referred to as scaling , is important for the effective utilisation of data from large ionospheric sounder networks. Due to the Earth's magnetic field, the ionosphere is birefringent at radio frequencies, so a VIS will typically see two distinct returns for each frequency. For the automatic scaling of ionograms, it is highly desirable to be able to separate the two modes. Defence Science and Technology (DST) Group has developed a new VIS solution which is based on direct digital receiver technology and includes an algorithm to separate the O and X -modes. This algorithm can provide high quality separation even in difficult ionospheric conditions. In this paper we describe the algorithm and demonstrate its consistency and reliability in successfully separating 99.4% of the ionograms during a 27-day experimental campaign under sometimes demanding ionospheric conditions.

Description: [1]  Near-surface heterogeneities produce diffractions in common offset ground-penetrating radar (GPR) data from the Gnangara Groundwater Mound, north of Perth, Western Australia. These diffracted wavefields can be enhanced and show a dispersion pattern if they propagate along a waveguide caused by a low velocity surface layer, such as moist sand on top of dry sand. Until now, GPR waveguide dispersion has been analyzed and inverted using common midpoint data. Using numerical modeling, we demonstrate that the same dispersion information can also be recovered from a diffracted electromagnetic wavefield recorded with common offset geometry. Frequency-slowness analysis of shallow diffractions in common offset GPR field data reveals high resolution dispersion curves. Inverting picked dispersion maxima to modeled curves (i.e., modal wave propagation in waveguide layer) allows estimation of waveguide height and velocities of waveguide and the underlying material. Data analysis in the frequency-wavenumber domain provides an alternative technique for extracting dispersion curves. Preliminary results validate this approach, which could be favorable in large-scale applications due to minimal processing requirement and inherent yet adjustable spatial averaging. The differences between waveguide parameters recovered from two surveys appear to be consistent with seasonal changes in moisture content and lateral changes due to variations in depositional environment. Our approach presents a new method to quantify the shallow dielectric permittivity structure of the subsurface from common offset gathers—the most commonly acquired type of GPR data. Potential applications of this method include estimation of shallow moisture distribution, early target identification for unexploded ordnance (UXO) detection, concrete slab characterization, pedological investigations, or planetary exploration.