The role of FAST in pulsar timing arrays     

George Hobbs  Shi Dai  Richard N.Manchester  Ryan M.Shannon  Matthew Kerr  Ke-Jia Lee  Ren-Xin Xu 《天文和天体物理学研究(英文版)》2019,(2)

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) will become one of the world-leading telescopes for pulsar timing array(PTA) research. The primary goals for PTAs are to detect(and subsequently study) ultra-low-frequency gravitational waves, to develop a pulsar-based time standard and to improve solar system planetary ephemerides. FAST will have the sensitivity to observe known pulsars with significantly improved signal-to-noise ratios and will discover a large number of currently unknown pulsars. We describe how FAST will contribute to PTA research and show that jitter-and timing-noise will be the limiting noise processes for FAST data sets. Jitter noise will limit the timing precision achievable over data spans of a few years while timing noise will limit the precision achievable over many years.  相似文献   

Edgar Hynes Thompson Centenary     

S. Thompson    K. B. Atkinson 《The Photogrammetric Record》2010,25(129):47-54

A significant landmark for British and international photogrammetry, as well as for this journal, occurred in January 2010 with the centenary of the birth of E. H. Thompson. Soldier and academic, polymath and wit, his scholarly contribution to our discipline has endured long after his too early death in 1976. So too have the vivid memories of those who worked with him or who were taught by him. This centenary tribute has been written by an author, E. H. Thompson's first cousin once removed, who has researched the Thompson family genealogy. The second author was a student and then an academic colleague of Thompson as well as being Assistant Editor of this journal for 11 years under Thompson's editorship.  相似文献   

Edgar Hynes Thompson: a collection of centenary reminiscences     

Collected  compiled by K. B. Atkinson 《The Photogrammetric Record》2010,25(129):55-68

The idea for this collection of memories of E. H. Thompson began as a suggestion to potential contributors for anything from "a couple of sentences to a couple of paragraphs". Both their willingness to write and the length of some contributions show how influential Thompson has been in the lives of so many of his colleagues and students. Contributors include two past-presidents of the International Society for Photogrammetry and Remote Sensing and six past-presidents of the Photogrammetric Society. Three longer essays are published as separate contributions to this feature.  相似文献   

Evaluating post-hurricane impacts in co-management areas: a framework for expert consensus     

Diaz  John  Carnevale  Shannon  Millett  Cheryl  Abd-Elrahman  Amr  Britt  Katie 《Natural Hazards》2020,103(2):1905-1916

Natural Hazards - Natural ecosystems are characterized as dynamic systems that evolve through natural patterns of disturbance. Land managers can work within this system of natural disturbance by...  相似文献   

High-resolution X-ray fluorescence profiling of hybrid event beds: Implications for sediment gravity flow behaviour and deposit structure     

Arif Hussain  Peter D. W. Haughton  Patrick M. Shannon  Jonathan N. Turner  Colm S. Pierce  Arnau Obradors-Latre  Simon P. Barker  Ole J. Martinsen 《Sedimentology》2020,67(6):2850-2882

Hybrid event beds form when turbidity currents that transport or locally acquire significant quantities of mud decelerate. The mud dampens turbulence driving flow transformations, allowing both mud and sand to settle into dense, near-bed fluid layers and debris flows. Quantifying details of the mud distribution vertically in what are often complex tiered deposits is critical to reconstructing flow processes and explaining the diverse bed types left by mud-bearing gravity flows. High-resolution X-ray fluorescence core scanning provides continuous vertical compositional profiles that can help to constrain mud distribution at sub-millimetre scale, offering a significant improvement over discrete sampling. The approach is applied here to cores acquired from the Pennsylvanian Ross Sandstone Formation, western Ireland, where a range of hybrid event beds have been identified. Raw X-ray fluorescence counts are calibrated against element concentrations and mineral abundances determined on coincident core plugs, with element and element log-ratios used as proxies to track vertical changes in abundances of quartz, illite (including mica), chlorite and calcite cement. New insights include ‘stepped’ (to higher values) as opposed to ‘saw-tooth’ vertical changes in mud content and the presence of compositional banding that would otherwise be overlooked. Hybrid event beds in basin floor sheets that arrived ahead of the prograding fan system have significantly cleaner sandy components than those in mid-fan lobes. The latter may imply that the heads of the currents emerging from mid-fan channels entrained significant mud immediately before they collapsed. Many of the H3 debrites are bipartite with a sandier H3a division attributed to re-entrainment and mixing of a trailing debris or fluid mud flow (H3b) with sand left by the forward part of the flow. Hybrid event bed structure may thus partly reflect substrate interaction and mixing during deposition, and the texture of the bed divisions may not simply mirror those in the suspensions from which they formed.  相似文献   

Population vulnerability models for asteroid impact risk assessment   总被引：1，自引：0，他引：1       下载免费PDF全文

Clemens M. Rumpf  Hugh G. Lewis  Peter M. Atkinson 《Meteoritics & planetary science》2017,52(6):1082-1102

An asteroid impact is a low probability event with potentially devastating consequences. The Asteroid Risk Mitigation Optimization and Research (ARMOR) software tool calculates whether a colliding asteroid experiences an airburst or surface impact and calculates effect severity as well as reach on the global map. To calculate the consequences of an impact in terms of loss of human life, new vulnerability models are derived that connect the severity of seven impact effects (strong winds, overpressure shockwave, thermal radiation, seismic shaking, ejecta deposition, cratering, and tsunamis) with lethality to human populations. With the new vulnerability models, ARMOR estimates casualties of an impact under consideration of the local population and geography. The presented algorithms and models are employed in two case studies to estimate total casualties as well as the damage contribution of each impact effect. The case studies highlight that aerothermal effects are most harmful except for deep water impacts, where tsunamis are the dominant hazard. Continental shelves serve a protective function against the tsunami hazard caused by impactors on the shelf. Furthermore, the calculation of impact consequences facilitates asteroid risk estimation to better characterize a given threat, and the concept of risk as well as its applicability to the asteroid impact scenario are presented.  相似文献   

Co-management of sea turtle fisheries: Biogeography versus geopolitics     

Lisa M. Campbell  Jennifer J. Silver  Noella J. Gray  Sue Ranger  Annette Broderick  Tatum Fisher  Matthew H. Godfrey  Shannon Gore  John Jeffers  Corrine Martin  Andrew McGowan  Peter Richardson  Carlos Sasso  Lorna Slade  Brendan Godley 《Marine Policy》2009

Co-management between local communities and government agencies is promoted as a strategy to improve fisheries management. This paper considers the potential for co-management of sea turtle fisheries within four UK Overseas Territories (OTs) in the Caribbean, and for co-ordinated management among those territories. We focus on fisher incentives for engaging in co-management and on the potential to scale up co-management to a regional level. This paper presents data from Anguilla, British Virgin Islands, Montserrat, and Turks and Caicos Islands, where 110 turtle fishers participated in a socio-economic survey undertaken as part of the ‘Turtles in the UK Overseas Territories in the Caribbean’ project. Based on three established criteria for co-management (perceived crisis in stock, willingness to participate and community cohesion), results suggest that fisher support for co-management exists within each OT, but the extent of support for and views of specific management interventions varies among OTs. The implications of results for co-management in each territory, and for establishing co-ordinated management regimes in the region, are discussed in the context of current debates about the nature of resources and scalar (mis)matches between resource and management regimes.  相似文献   

Variability and predictability of Antarctic krill swarm structure   总被引：6，自引：0，他引：6  

Geraint A. Tarling  Thor Klevjer  Sophie Fielding  Jon Watkins  Angus Atkinson  Eugene Murphy  Rebecca Korb  Mick Whitehouse  Russell Leaper 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(11):1994-2012

Swarming is a fundamental part of the life of Euphausia superba, yet we still know very little about what drives the considerable variability in swarm shape, size and biomass. We examined swarms across the Scotia Sea in January and February 2003 using a Simrad EK60 (38 and 120 kHz) echosounder, concurrent with net sampling. The acoustic data were analysed through applying a swarm-identification algorithm and then filtering out all non-krill targets. The area, length, height, depth, packing-concentration and inter-swarm distance of 4525 swarms was derived by this method. Hierarchical clustering revealed 2 principal swarm types, which differed in both their dimensions and packing-concentrations. Type 1 swarms were generally small (<50 m long) and were not very tightly packed (<10 ind. m⁻³), whereas type 2 swarms were an order of magnitude larger and had packing concentrations up to 10 times greater. Further sub-divisions of these types identified small and standard swarms within the type 1 group and large and superswarms within the type 2 group. A minor group (swarm type 3) was also found, containing swarms that were isolated (>100 km away from the next swarm). The distribution of swarm types over the survey grid was examined with respect to a number of potential explanatory variables describing both the environment and the internal-state of krill (namely maturity, body length, body condition). Most variables were spatially averaged over scales of 100 km and so mainly had a mesoscale perspective. The exception was the level of light (photosynthetically active radiation (PAR)) for which measurements were specific to each swarm. A binary logistic model was constructed from four variables found to have significant explanatory power (P<0.05): surface fluorescence, PAR, krill maturity and krill body length. Larger (type 2) swarms were more commonly found during nighttime or when it was overcast during the day, when surface fluorescence was low, and when the krill were small and immature. A strong pattern of diel vertical migration was not observed although the larger and denser swarms tended to occur more often at night than during the day. The vast majority of krill were contained within a minor fraction of the total number of swarms. These krill-rich swarms were more common in areas dominated by small and immature krill. We propose that, at the mesoscale level, the structure of swarms switches from being predominantly large and tightly packed to smaller and more diffuse as krill grow and mature. This pattern is further modulated according to feeding conditions and then level of light.  相似文献   

Desolate landscapes: Ice‐Age settlement in Eastern Europe     

Shannon P. McPherron 《Geoarchaeology》2003,18(8):904-905

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