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The extraordinary linear polarisation structure of the Southern Centaurus a lobe revealed by ASKAP
No full textWe present observations of linear polarisation in the southern radio lobe of Centaurus A, conducted during commissioning of the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. We used 16 antennas to observe a 30 square degree region in a single 12-h pointing over a 240 MHz band centred on 913 MHz. Our observations achieve an angular resolution of 26
733 arcseconds (480 parsecs), a maximum recoverable angular scale of 30 arcminutes, and a full-band sensitivity of 85 \u3bc Jy beam 121 . The resulting maps of polarisation and Faraday rotation are amongst the most detailed ever made for radio lobes, with order 10 5 resolution elements covering the source. We describe several as-yet unreported observational features of the lobe, including its detailed peak Faraday depth structure, and intricate networks of depolarised filaments. These results demonstrate the exciting capabilities of ASKAP for widefield radio polarimetry.Peer reviewed: YesNRC publication: Ye
The transcriptional landscape of polyploid wheat
No full textINTRODUCTION: Polyploidy, arising from whole-genome duplication or interspecific hybridization, is ubiquitous across the plant and fungal kingdoms. The presence of highly related genes in polyploids, referred to as homoeologs, has been proposed to confer adaptive plasticity\u2014for example, through neofunctionalization of duplicated genes or tissue-specific expression. This plasticity has facilitated the domestication and adaptation of major polyploid crops (e.g., wheat, cotton, and coffee). However, despite its likely importance, we have a limited understanding of the effect of polyploidy on gene expression and the extent to which homoeologs are similar or different in their expression patterns across development and tissues. RATIONALE: Bread wheat is a polyploid derived from the hybridizations between three distinct diploid species and is an informative system for analyzing the effects of recent polyploidy on gene expression. Understanding the coordination of homoeologs and identifying the mechanisms associated with these processes should help define strategies to improve trait biology in a crop that provides more than 20% of the protein and caloric intake of humans. RESULTS: Here we leverage 850 wheat RNA-sequencing samples, alongside the annotated genome, to determine the similarities and differences between homoeolog expression across a range of tissues, developmental stages, and cultivars. On average, ~30% of wheat homoeolog triads (composed of A, B, and D genome copies) showed nonbalanced expression patterns, with higher or lower expression from a single homoeolog with respect to the other two. These differences between homoeologs were associated with epigenetic changes affecting DNA methylation and histone modifications. Although nonbalanced homoeolog expression could be partially predicted by expression in diploid ancestors, large changes in relative homoeolog expression were observed owing to polyploidization. Our results suggest that the transposable elements in promoters relate more closely to the variation in the relative expression of homoeologs across tissues than to a ubiquitous effect across all tissues. We found that homoeologs with the highest inter-tissue variation had promoters with more frequent transposable element insertions and more varied cis-regulatory elements than homoeologs that were stable across tissues. We also identified expression asymmetry along wheat chromosomes. Homoeologs with the largest inter-tissue, inter-cultivar, and coding sequence variation were most often located in the highly recombinogenic distal ends of chromosomes. These transcriptionally dynamic homoeologs are under more relaxed selection pressure, potentially representing the first steps toward functional innovation through neo- or subfunctionalization. We generated tissue- and stress-specific coexpression networks that reveal extensive coordination of homoeolog expression throughout development. These networks, alongside detailed gene expression atlases (www.wheat-expression.com and http://bar.utoronto.ca), lay the groundwork to identify candidate genes influencing agronomic traits in wheat. CONCLUSION: This study provides detailed insights into the transcriptional landscape of bread wheat, an evolutionarily young polyploid. Our work shows that homoeolog expression patterns in bread wheat have been shaped by polyploidy and are associated with both epigenetic modifications and variation in transposable elements within promoters of homoeologous genes. The extensive datasets and analyses presented here provide a framework that can help researchers and breeders develop strategies to improve crops by manipulating individual or multiple homoeologs to modulate trait responses.Peer reviewed: YesNRC publication: Ye
Development of an interactive, web-based decision support system to facilitate marine renewable energy site selection
No full textThe authors present recent progress in the development of the British Columbia Marine Energy Resource Atlas (hereafter referred to as the \u201cAtlas\u201d). The Atlas is a web-based geospatial decision support system and was developed to assist marine renewable energy stakeholders with preliminary site selection and feasibility investigations in the rivers and coastal waters of British Columbia, Canada. The Atlas offers a clean and simple interface through which users are able to interact with the underlying geospatial data and customize investigations to fit their specific design and development criteria. The Atlas represents a uniquely flexible and accessible decision support system that can be operated online via a web browser and does not require any specialized geographic information system software. Furthermore, the Atlas is the first marine renewable energy decision support system to offer support for tidal, wave, and river hydrokinetic resources under a common system and interface.Peer reviewed: YesNRC publication: Ye
Risks to marine pipelines from drifting ice: gathering the evidence
No full textMarine pipelines in ice-prone waters are exposed to a number of environmental threats that do not exist in warmer waters. Of particular concern is the damage from ice features such as pressure ridges that drift into shallow areas. The ice keel comes in contact with the seabed and, as the ice feature keeps drifting, it may gouge the seabed to some depth and for considerable distances. Trenching and burial are seen as the best means of protecting these structures, but adequate depth relies on adequate knowledge of these events. This is obtained in various ways. Actual, real-scale events provide valuable information. Seabed mapping allows an appreciation of gouging activity in the target sector. Physical experiments can generate a nearly complete picture of these events, and can be used to validate numerical models. A description is presented of an abandoned marine pipeline in Northern Canada, which represents a rare test case scenario. Plans to conduct field investigations on that pipeline are being considered.Peer reviewed: YesNRC publication: Ye
The subsea Drake pipeline: a challenging case study to check design effectiveness against drifting ice action
No full textThe Drake pipeline is located offshore Melville Island, in the Canadian High Arctic. It was built on-site in 1977-78 and connected to a natural gas production well, which operated for only a few months. The well was plugged in 1995 and the pipeline was abandoned. The pipeline extends from the shoreline to the wellhead located about one kilometer offshore to a water depth of 55 meters. It is buried at the shoreline crossing, to a target depth of 1.5 meters below sea bottom. A system to generate a frozen soil shield was also devised for further protection against drifting ice. Also, a berm made from ice and gravel was built at the water line. Field investigations could prove highly instructive to assess the state of the structure, and provide guidelines for design of future pipelines in high risks areas. However, significant technical and logistical challenges would face that venture, namely a \u2018no physical contact\u2019 (with the pipeline) restriction from the property owner, which leads to difficulty in understanding what has occurred to the pipeline beneath the soil, and a propensity for the region to be covered with a very thick ice cover.Peer reviewed: YesNRC publication: Ye
A semi-empirical pod model for USCG icebreaker mackinaw. Part I. The empirical data
No full textA semi-empirical pod model is developed based on experimental data for the USCGC Mackinaw to predict propulsion forces for the icebreaker driven by twin podded propulsors. The experiments are conducted in straight-ahead motion with the azimuth angle of one of the twin pods steered in a range from 0 to 180o. In this pod model, assumption was made to extend the test data to the full range of 360o azimuth angles and advance coefficients. Analysis was then performed to allow these test data for application of any planar motion including turning by considering hull-pod interaction. This is Part I of a two-part paper. In this paper, the results from ice tank tests are presented. These include steering moment generated by the propulsors, thrust and torque of the propellers and the forces exerted on the hull at the location of the connection of the propulsors. The procedure to extend the empirical data to the full range is then presented. The agreement between static and dynamic data and the symmetry of the data is considered.Peer reviewed: YesNRC publication: Ye
Hydrodynamic analysis of core-loc units via controlled drop tests
No full textPeer reviewed: YesNRC publication: Ye
