Periodic nulls in the pulsar B1133+16     

Jeffrey L. Herfindal  Joanna M. Rankin 《Monthly notices of the Royal Astronomical Society》2007,380(2):430-436

Numerous studies of the brightest Cambridge pulsar, B1133+16, have revealed little order in its individual pulses, apart from a weak 30-odd-rotation-period fluctuation feature and that some 15 per cent of the star's pulsars are 'nulls'. New Arecibo observations confirm this fluctuation feature and that it modulates all the emission, not simply the 'saddle' region. By replacing each pulse with a scaled version of the average profile, we were able to quench all subpulse modulation and thereby demonstrate that the star's 'null' pulses exhibit a similar periodicity. A subbeam carousel model with a sparse and irregular 'beamlet' population appears to be compatible with these characteristics.  相似文献   

Ecogeomorphic state variables and phase‐space construction for quantifying the evolution of vegetated aeolian landscapes     

Andreas C. W. Baas  Joanna M. Nield 《地球表面变化过程与地形》2010,35(6):717-731

Cellular automaton modelling for the simulation of dune field formation and evolution has developed progressively in aeolian geomorphology in the last decade or so. A model that incorporates the effects of vegetation and its interactions with geomorphic landscape development – the Discrete Ecogeomorphic Aeolian Landscapes (DECAL) model – can replicate a number of important visual and qualitative aspects of the complex evolution of aeolian dune landscapes under the influence of vegetation dynamics in coastal environments. A key challenge in this research area is the analysis and comparison of both simulated and real‐world vegetated dune landscapes using objective and quantifiable principles. This study presents a methodological framework or protocol for numerically quantifying various ecogeomorphic attributes, using a suite of mathematically defined landscape metrics, to provide a rigorous and statistical evaluation of vegetated dune field evolution. Within this framework the model parameter space can be systematically explored and simulation outcomes can be methodically compared against real‐world landscapes. Based on a simplified scenario of parabolic dunes developing out of blow‐outs the resulting dune field realizations are investigated as a function of variable growth vigour of two simulated vegetation types (pioneer grass and successional woody shrub) by establishing a typological phase‐diagram of different landscape classes. The set of simulation outcomes furthermore defines a higher‐dimensional phase‐space, whose axes or dimensions can be interpreted by analysing how individual ecogeomorphic landscape metrics, or state variables, contribute to the data distribution. Principal component analysis can reduce this to a visual three‐dimensional (3D) phase‐space where landscape evolution can be plotted as time‐trajectories and where we can investigate the effects of changing environmental conditions partway through a simulation scenario. The use of landscape state variables and the construction of a 3D phase‐space presented here may provide a general template for quantifying many other eco‐geomorphic systems on the Earth's surface. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Atmospheric dust contribution to deep-sea particle fluxes in the subtropical Northeast Atlantic     

Juliane Brust  Joanna J. Waniek 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(8):988-998

The lithogenic flux of sediment trap material was analyzed from a three year time series (February 2002–March 2005) at 2000 m depth in the Northeast Atlantic (Kiel 276, 33°N, 22°W) with regards to the seasonal and interannual variability of flux intensity and mineralogy—by applying an automated particle SEM-EDX analysis (scanning electron microscope-energy dispersive X-ray analysis). The lithogenic flux shows strong interannual variations with highest lithogenic flux rates occurring during January–February and April–March coupled to the total particle flux. Mean lithogenic flux rates for the sample years are 7.1 (2002–2003), 5.1 (2003–2004) and 16.1 mg m^?2 d^?1 (2004–2005). Mineral assemblages from the three sample years reveal distinct major minerals related to specific source regions. Clay minerals dominate the lithogenic fraction within the years 2002 and 2004 with illite (2002–2003) and palygorskite (2003–2004) being the major clay minerals. During the year 2004–2005, quartz is the major lithogenic mineral accompanied by smectite. The mineral assemblages hint to a mixture of North African source areas with dominant sources in Mauritania and north western parts of NW Africa for the years 2002–2004 and central Sahara (Algeria–Mali) within the year 2004–2005.  相似文献   

Vertical circulation in shallow tidal inlets and back-barrier basins     

Emil V. Stanev  Burghard W. Flemming  Alex Bartholomä  Joanna V. Staneva  Jörg-Olaf Wolff 《Continental Shelf Research》2007

  相似文献   

Compliance and emission trading rules for asymmetric emission uncertainty estimates   总被引：3，自引：3，他引：0  

Zbigniew Nahorski  Joanna Horabik 《Climatic change》2010,103(1-2):303-325

Greenhouse gases emission inventories are computed with rather low precision. Moreover, their uncertainty distributions may be asymmetric. This should be accounted for in the compliance and trading rules. In this paper we model the uncertainty of inventories as intervals or using fuzzy numbers. The latter allows us to better shape the uncertainty distributions. The compliance and emission trading rules obtained generalize the results for the symmetric uncertainty distributions that were considered in the earlier papers by the present authors (Nahorski et al., Water Air & Soil Pollution. Focus 7(4–5):539–558, 2007; Nahorski and Horabik, 2007, J Energy Eng 134(2):47–52, 2008). However, unlike in the symmetric distribution, in the asymmetric fuzzy case it is necessary to apply approximations because of nonlinearities in the formulas. The final conclusion is that the interval uncertainty rules can be applied, but with a much higher substitutional noncompliance risk, which is a parameter of the rules.  相似文献   

Reply to Comment on ‘Towards an Interpretation of Historical Droughts in Northern Nigeria’     

Aondover Tarhule  Ming-Ko Woo 《Climatic change》1999,41(2):261-262

  相似文献   

Synthesis of recent ESPL research: aeolian processes and landforms     

Joanna E. Bullard 《地球表面变化过程与地形》2008,33(13)

  相似文献   

Volcano-seismic crisis in Montserrat,West Indies, 1966–67     

J. B. Shepherd  J. F. Tomblin  D. A. Woo 《Bulletin of Volcanology》1971,35(1):143-162

The Soufriere Hills volcano in the south-eastern part of Montserrat erupted pyroclast flows as recently as A. D. 1646 ± 54 years and must therefore be considered dormant, not extinct. The highly destructive nature of pyroclast flow eruptions makes it imperative that such activity should be predicted and, if the threat of eruption becomes sufficiently large, the population should be moved to a sale distance from the volcano. Sharp increases in seismic and solfataric activity occurred in 1966 and these events indicated the abnormally high risk of an eruption in the near future. A network of four short period seismographs was established in the island in May 1966 and between this date and the end of 1967, 723 local earthquakes were recorded, of which 32 were reported felt in the island. Hypocentres were determined for 189 of these earthquakes, and most of these lay in a WNW to ESE belt beneath the Soufriere Hills, at depths of less than 15 km. The average rate of seismic energy release decreased with time throughout the series but there was a strong seasonal variation with maxima in May and November–December of each year. The average depth of the earthquakes decreased from 5.2 km in April and May 1966 to a minimum of 2.8 km from July to September 1966. After September the mean focal depths increased again and by the end of the crisis in November 1967 the mean depth was 9.7 km. Measurements carried out using water-tube tiltmeters showed that the region 2–3 km south-east of the Soufriere Hills was doming upwards until January 1967, then subsided between January–March 1967 and finally rose again at a slower rate between March and September 1967. Heat flow from Galway’s Soufriere which was 3 × 10⁵ cal/sec in 1954 increased to a maximum of 2 × 10⁵ cal/sec in October 1966, then declined to 5 × 10⁵ cal/sec in September 1967. The earthquake series was not the aftershock sequence of any major tectonic earthquake, and only two hypocentres were determined at depths greater than 15 km. It is concluded that magma was intruded into the upper crust beneath the Soufriere Hills volcano and that the earthquakes and other phenomena resulted from the upward migration of this magma.  相似文献   

Climate change and transportation in Northern Canada: an integrated impact assessment     

Steve Lonergan  Richard Difrancesco  Ming-Ko Woo 《Climatic change》1993,24(4):331-351

The physical and economic impacts of climate warming in the Mackenzie River Valley, Northwest Territories, Canada are estimated using a combination of stochastic modelling, econometric-modelling and input-output analysis. The attempt was to illustrate the utility of using analytical models for long-term impact assessment as well as to estimate the potential impacts from projected climate warming in the region. A scenario approach, based on three global circulation models, was used, with an emphasis on modelling climate variability, river ice conditions and economic impacts. The transportation system was used as a central focus linking the physical and socio-economic components. Despite the significant warming projected for the region, results show the economic impacts from changes in transportation to be relatively minor, with the greatest changes being in the tertiary, or service, sector.  相似文献   

Walrus (Odobenus rosmarus) predation on adult thick-billed murres (Uria lomvia) at Coats Island, Nunavut, Canada     

Mark L. Mallory  Kerry Woo  Anthony J. Gaston  W. Eric Davies  Pierre Mineau 《Polar research》2004,23(1):111-114

Although the diet of walrus ( Odobenus rosmarus ) is considered varied, records of walrus consuming marine birds are rare in the published literature. In 2001 and 2002 we observed walrus foraging on adult thick-billed murres ( Uria lomvia ) at Coats Island in Nunavut, Canada. Approximately 46% of the attacks on murres were successful, and as many as 67 murres may have been killed in one day in August 2002. All soft parts of the murres were sucked out, with carcasses of only bones, feathers and skin left floating on the water. The extent to which predation on seabirds by walrus occurs across the eastern Arctic is unknown, but it could represent an important source of mortality for murres at some breeding colonies.  相似文献