Properties of hot stars in the Wolf--Rayet galaxy NGC 5253 from ISO-SWS spectroscopy     

Paul A. Crowther  S. C. Beck  Allan J. Willis  Peter S. Conti  Patrick W. Morris  Ralph S. Sutherland 《Monthly notices of the Royal Astronomical Society》1999,304(3):654-668

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Cosmic-ray positrons: are there primary sources?     

Stphane Coutu  Steven W. Barwick  James J. Beatty  Amit Bhattacharyya  Chuck R. Bower  Christopher J. Chaput  Georgia A. de Nolfo  Michael A. DuVernois  Allan Labrador  Shawn P. McKee  Dietrich Müller  James A. Musser  Scott L. Nutter  Eric Schneider  Simon P. Swordy  Gregory Tarl  Andrew D. Tomasch  Eric Torbet 《Astroparticle Physics》1999,11(4):208-435

Galactic cosmic rays consist of primary and secondary particles. Primary cosmic rays are thought to be energized by first order Fermi acceleration processes at supernova shock fronts within our Galaxy. The cosmic rays that eventually reach the Earth from this source are mainly protons and atomic nuclei, but also include electrons. Secondary cosmic rays are created in collisions of primary particles with the diffuse interstellar gas. They are relatively rare but carry important information on the Galactic propagation of the primary particles. The secondary component includes a small fraction of antimatter particles, positrons and antiprotons. In addition, positrons and antiprotons may also come from unusual sources and possibly provide insight into new physics. For instance, the annihilation of heavy supersymmetric dark matter particles within the Galactic halo could lead to positrons or antiprotons with distinctive energy signatures. With the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have measured the abundances of positrons and electrons at energies between 1 and 50 GeV. The data suggest that indeed a small additional antimatter component may be present that cannot be explained by a purely secondary production mechanism. Here we describe the signature of the effect and discuss its possible origin.  相似文献   

A spatially resolved 'inside-out' outburst of IP Pegasi     

N. A. Webb  T. Naylor  Z. Ioannou  W. J. Worraker  J. Stull  A. Allan  R. Fried  N. D. James  D. Strange 《Monthly notices of the Royal Astronomical Society》1999,310(2):407-413

We present a comprehensive photometric data set taken over the entire outburst of the eclipsing dwarf nova IP Peg in 1997 September/October. Analysis of the light curves taken over the long rise to the peak-of-outburst shows conclusively that the outburst started near the centre of the disc and moved outwards. This is the first data set that spatially resolves such an outburst. The data set is consistent with the idea that long rise times are indicative of such 'inside-out' outbursts. We show how the thickness and the radius of the disc, along with the mass transfer rate, change over the whole outburst. In addition, we show evidence of the secondary and the irradiation thereof. We discuss the possibility of spiral shocks in the disc; however, we find no conclusive evidence of their existence in this data set.  相似文献   

Molecular biomarker evidence of origins and transport of organic matter in sediments of the Pearl River estuary and adjacent South China Sea   总被引：3，自引：0，他引：3  

Jianfang Hu  Ping&#x;an Peng  Allan R. Chivas 《Applied Geochemistry》2009,24(9):1666-1676

Surface sediments from the subtropical Pearl River estuary and adjacent South China Sea were investigated by molecular organic geochemical methods to determine the composition, distribution and origin of extractable lipids (n-alkanes, n-alkanols and sterols). The absolute and organic C normalized concentrations of total alkane, n-alkanol, and sterol ranged from 0.16 to 2.67 μg g⁻¹ and 0.9 to 12.3 μg g⁻¹ OC, 24.4 to 427.3 ng g⁻¹ and 63.2 to 1966.7 ng g⁻¹ OC, and 9.0 to 493.5 ng g⁻¹ and 58.4 to 1042.4 ng g⁻¹ OC, respectively. The spatial distributions of these biomarkers indicated that terrestrial-derived molecular biomarkers such as long-chain n-alkanes, n-alkanols and plant-derived sterols were higher at the river mouth and along the coastline, suggesting that a higher proportion of terrestrial particulate organic matter was deposited there. Relatively lower amounts of marine-derived biomarkers such as short-chain n-alkanes, algal sterols at the river mouth reflected the lower primary productivity due to high turbidity. The spatial patterns of these biomarkers were partially related to the estuarine processes and conditions, evidencing an increased terrestrial signal from the Pearl River mouth to the inner estuary, and enhanced marine conditions further offshore.  相似文献   

Tides in the Tongan Region of the Pacific Ocean     

John L. Luick  R. Falconer Henry 《Marine Geodesy》2013,36(1):17-29

Tidal levels and currents in the Tongan region of the Pacific were simulated using a two-dimensional frequency-domain finite element model. The eight major diurnal and semidiurnal tidal constituents were modeled successfully, using open boundary conditions taken from a global tidal model based on the Topex/Poseidon satellite altimeter. Comparison of model results with observations from the single tide gauge site in the area were later used to adjust the boundary conditions. The validity of omitting horizontal eddy viscosity from the finite element model was checked by running an equivalent finite difference model. The results show that although the submarine Tongan ridge does not appear to trap tidal energy, there are residual tidal currents and possible recirculations which are capable of influencing biological productivity around Tonga. The model results are reduced to a simple method for predicting tidal heights in outlying areas, based only on the tidal calendar for the capital, Nuku'alofa.  相似文献   

Energetic Constraints on Precipitation Under Climate Change     

Paul A. O’Gorman  Richard P. Allan  Michael P. Byrne  Michael Previdi 《Surveys in Geophysics》2012,33(3-4):585-608

Energetic constraints on precipitation are useful for understanding the response of the hydrological cycle to ongoing climate change, its response to possible geoengineering schemes, and the limits on precipitation in very warm climates of the past. Much recent progress has been made in quantifying the different forcings and feedbacks on precipitation and in understanding how the transient responses of precipitation and temperature might differ qualitatively. Here, we introduce the basic ideas and review recent progress. We also examine the extent to which energetic constraints on precipitation may be viewed as radiative constraints and the extent to which they are confirmed by available observations. Challenges remain, including the need to better demonstrate the link between energetics and precipitation in observations and to better understand energetic constraints on precipitation at sub-global length scales.  相似文献   

Spatial and temporal variation of organic carbon in the northern South China Sea revealed by sedimentary records   总被引：2，自引：0，他引：2  

Jianfang Hu  Xuesong Sun  Ping'an Peng  Gan Zhang  Allan R. Chivas 《Quaternary International》2009,206(1-2):46

Three sediment cores were taken from the Pearl River estuary and adjacent northern South China Sea (SCS). These sediment cores span the time interval 1900–2000 AD. The stratigraphy of the concentration, the ratio of total organic carbon (TOC) to total nitrogen (TN) and stable isotope (δ¹³C_org) of organic carbon (OC) from three high-resolution sediment cores were analyzed. The stratigraphic profiles of OC concentration, TOC/TN ratios and δ¹³C_org for the near past 100 yrs indicate that terrestrial organic matter decreases from 68.3% to 27.4% of the TOC in the Pearl River estuary, while Dapeng Bay (offshore east of Hong Kong) apparently had throughout little terrestrial organic matter input. The highest deposited OC occurs at the Humen River mouth and the OC concentrations are higher in the outer estuary than in the inner shelf of the northern SCS. The deposited OC at the River mouth increased with time, which could be caused by the high precipitation of land-derived organic matter and the high input of terrestrial organic matter, which is likely related to the rapid urbanization and industrial development in the Pearl River Delta since the 1970s. The OC concentrations did not exhibit an obvious increase with time in most areas of the Pear River estuary and adjacent inner shelf of the SCS, but the algal-derived OC concentration inferred from the δ¹³C_org values increased with time especially from 1980 to 2000 in the outer Pearl River estuary and Dapeng Bay. This increase is presumably caused by enhanced primary marine productivity supported by higher anthropogenic nutrient inputs.  相似文献   

Procedures for woody vegetation surveys in the Kazgail rural council area,Kordofan, Sudan     

Allan Falconer  Matthew D. Cross  Donald G. Orr 《国际地球制图》2013,28(3):49-58

Efforts to reforest parts of the Kordofan Province of Sudan are receiving support from international development agencies. These efforts include planning and implementing reforestation activities that require the collection of natural resources and socioeconomic data, and the preparation of base maps. A combination of remote sensing, geographic information system and global positioning systems procedures are used in this study to meet these requirements.

Remote sensing techniques were used to provide base maps and to guide the compilation of vegetation resources maps. These techniques provided a rapid and efficient method for documenting available resources. Pocket‐sized global positioning system units were used to establish the location of field data collected for mapping and resource analysis. A microcomputer data management system tabulated and displayed the field data. The resulting system for data analysis, management, and planning has been adopted for the mapping and inventory of the Gum Belt of Sudan.  相似文献   

Formula of incipient velocity for flooded vehicles   总被引：3，自引：3，他引：0  

Junqiang Xia  Fang Yenn Teo  Binliang Lin  Roger A. Falconer 《Natural Hazards》2011,58(1):1-14

With the climate change caused by global warming, the occurrence probability of urban flooding due to flash floods has increased gradually. Flush floods propagate rapidly, which can lead to significant hazard to human life and property. Flood hazard to vehicles has become more noticeable and frequent in recent years. Therefore, it is important to investigate the behaviour of vehicles on flooded streets or roads. In the current study, a formula has been derived to predict the incipient velocity of flooded vehicles according to the mechanical condition of sliding equilibrium. A series of flume experiments were conducted using three types of scaled die-cast model vehicles, with two scales being tested for each type of vehicle. The experimental data obtained for the small-scale model vehicles were used to determine the two parameters in the derived formula, and the prediction accuracy of this formula was validated using the experimental data obtained for the large-scale model vehicles. Finally, the corresponding incipient velocities under various incoming depths were computed using this formula for these three prototype vehicles. It is found that for a specified vehicle, the value of incipient velocity reaches its minimum as the incoming flow depth approaches the height of the vehicle, and the smaller and lighter vehicle like Mini Cooper is the easiest to start sliding in floodwaters. The results can be used as a preliminary assessment to define the hazard to vehicles parking on flooded streets or roads.  相似文献   

Differences in the neighborhood: Structural variations in the carapace of shore crabs Carcinus maenas (Decapoda: Portunidae)     

Allan T. Souza  Martina I. Ilarri  Joana Campos  João C. Marques  Irene Martins 《Estuarine, Coastal and Shelf Science》2011

The present study compared the carapace structure of Carcinus maenas in two nearby sites (2 km apart) within Minho estuary, submitted to different physicochemical and ecological conditions (water temperature, pH, crabs’ density and sex ratio). The carapace structure of the carapace and chelae of the crabs presented significant differences between sampling sites (t-test; p < 0.01). The SIMPER analysis revealed that the Weight/CW and Thickness/CW ratios explained all the dissimilarities found among sites. Overall, the male carapace was proportionally thicker at station 2 (t-test; p < 0.01), while the female carapace was proportionally thicker at station 1 (t-test; p < 0.001). A thicker carapace can be advantageous when competing for food or a sexual partner. We hypothetized that, since at station 2, the density of individuals was twice higher than at station 1, it is likely that agonistic encounters are more frequent, thus favouring a thicker carapace.  相似文献