Smoothed Particle Hydrodynamics in cosmology: a comparative study of implementations     

R. J. Thacker  †  E. R. Tittley  ‡  F. R. Pearce  H. M. P. Couchman §  P. A. Thomas 《Monthly notices of the Royal Astronomical Society》2000,319(2):619-648

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The Deep Space 1 Encounter with Comet 19p/Borrelly     

Boice  D. C.  Soderblom  L. A.  Britt  D. T.  Brown  R. H.  Sandel  B. R.  Yelle  R. V.  Buratti  B. J.  Hicks  Nelson  Rayman  Oberst  J.  Thomas  N. 《Earth, Moon, and Planets》2000,89(1-4):301-324

NASA's Deep Space 1 (DS1) spacecraft successfully encountered comet 19P/Borrelly near perihelion and the Miniature Integrated Camera and Spectrometer (MICAS) imaging system onboard DS1 returned the first high-resolution images of a Jupiter-family comet nucleus and surrounding environment. The images span solar phase angles from 88° to 52°, providing stereoscopic coverage of the dust coma and nucleus. Numerous surface features are revealed on the 8-km long nucleus in the highest resolution images(47–58 m pixel). A smooth, broad basin containing brighter regions and mesa-likestructures is present in the central part of the nucleus that seems to be the source ofjet-like dust features seen in the coma. High ridges seen along the jagged terminator lead to rugged terrain on both ends of the nucleus containing dark patches and smaller series of parallel grooves. No evidence of impact craters with diameters larger thanabout 200-m are present, indicating a young and active surface. The nucleus is very dark with albedo variations from 0.007 to 0.035. Short-wavelength, infrared spectra from 1.3 to 2.6 μm revealed a hot, dry surface consistent with less than about10% actively sublimating. Two types of dust features are seen: broad fans and highlycollimated “jets” in the sunward hemisphere that can be traced to the surface. The source region of the main jet feature, which resolved into at least three smaller “jets” near the surface, is consistent with an area around the rotation pole that is constantly illuminated by the sun during the encounter. Within a few nuclear radii, entrained dustis rapidly accelerated and fragmented and geometrical effects caused from extended source regions are present, as evidenced in radial intensity profiles centered on the jet features that show an increase in source strength with increasing cometocentric distance. Asymmetries in the dust from dayside to nightside are pronounced and may show evidence of lateral flow transporting dust to structures observed in the nightside coma. A summary of the initial results of the Deep Space 1 Mission is provided, highlighting the new knowledge that has been gained thus far.  相似文献   

Erratum to “Cosmic-ray neutrino annihilation on relic neutrinos revisited: a mechanism for generating air showers above the Greisen–Zatsepin–Kuzmin cutoff” (Astropart. Phys. 11 (1999) 303–316)     

Thomas J. Weiler   《Astroparticle Physics》2000,12(4):379

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The effective source rocks in the north Cambay Basin, India     

A. Banerjee  M. Jha  A. K. Mittal  N. J. Thomas  K. N. Misra 《Marine and Petroleum Geology》2000,17(10):7

Source rock screening reveals five laterally extending potential sources (PS) in the Paleogene. The PSs are SR5 and SR6 in dominantly marine early Eocene to late Paleocene Cambay Shale formation, and SR7, SR8/9, and SR11/12 in dominantly freshwater early Paleocene Olpad formation. Only 3 PSs, SR11/12, SR8/9, and SR7 have attained vitrinite reflectance of 0.75% at 45, 7, and 2 mybp, respectively. Chromatographic and isotope data of oils and PS samples suggest that mainly the Olpad source rocks: SR7 and SR8/9 contributed to the discovered oils. The Cambay Shale source rocks, SR5 and SR6, contrary to the prevalent view, possibly have no significant contribution towards the accumulated oils.  相似文献   

Lead and Aroclor 1254 disrupt reproductive neuroendocrine function in Atlantic croaker     

I. A. Khan  P. Thomas 《Marine environmental research》2000,50(1-5):119-123

We have previously shown that lead (lead chloride) and a polychlorinated biphenyl (PCB) mixture (Aroclor 1254) can alter hypothalamic serotonin (5-hydroxytryptamine, 5-HT) content, and pituitary gonadotropin II (GTH II) release in vitro, in the Atlantic croaker (Micropogonias undulatus). In the present study we investigated whether impairment of the hypothalamic 5-HT pathway involves alterations in tryptophan hydroxylase (TPH), the rate-limiting enzyme in 5-HT biosynthesis, or monoamine oxidase (MAO), the catabolic enzyme. Aroclor 1254 (1 mg/kg body wt. for 30 days) significantly inhibited hypothalamic TPH activity without altering MAO activity, and caused a significant decline in 5-HT content. On the other hand, lead exposure (15 mg/kg body wt. for 30 days) only induced a slight decrease in hypothalamic 5-HT content and TPH activity, and a minor increase in MAO activity. However, both Aroclor 1254 and lead significantly inhibited the GTH II response to stimulation by a luteinizing hormone-releasing hormone analog (LHRHa) in vivo and caused reduced gonadal growth. These results demonstrate that impairment of hypothalamic serotonin metabolism by Aroclor 1254 involves inhibition of 5-HT synthesis, whereas lead does not exert a profound influence on 5-HT metabolism. The decline in 5-HT availability due to reduced 5-HT synthesis in the PCB-exposed fish may result in disruption of the stimulatory 5-HT-GnRH pathway controlling GTH II secretion leading to impairment of gonadal growth.  相似文献   

Radial transpression ridges: A new structural feature of complex impact craters     

Thomas KENKMANN  Ilka von DALWIGK 《Meteoritics & planetary science》2000,35(6):1189-1201

Abstract— The gravity‐driven collapse of complex impact craters induces the mass transfer of large rock volumes. In distal parts of a crater, inward movements dominate; whereas in the centre of an impact structure, outward movements occur if the central uplift collapses. The particle trajectory field is centro‐symmetric, which signifies that the conditions for plane‐strain deformation are not fullfilled. Converging particle trajectories can be compensated either by a bulk thickening of inward sliding masses (folding, repetition of rock units along thrust faults, plastic flow) or by the formation of localised radial transpression ridges (RTR) at the edges of individual landslides. In these transpression ridges, material is uplifted to accommodate the converging mass flow. Different modes of uplift are possible including radial folding, lateral overthrusting, and the formation of positive flower structures. A simple geometric model is used to estimate the amount of transpression thickening and bulk thickening of inward sliding masses on the base of volumetric considerations. The existence of RTRs is confirmed by structural investigations at the Siljan impact structure, Sweden, as well as at other complex impact craters on Earth.  相似文献   

Acoustic simulation of P-wave propagation in a heterogeneous spherical earth: numerical method and application to precursor waves to PKPdf     

Ch. Thomas  H. Igel  M. Weber  & F. Scherbaum 《Geophysical Journal International》2000,141(2):307-320

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Relationship between Age and Oxygen along Line W in the Northwest Atlantic Ocean     

Jordan L. Thomas  Darryn W. Waugh  Anand Gnanadesikan 《Ocean Science Journal》2020,55(2):203-217

The relationship between age and oxygen is one that is often assumed in oceanography to be relatively simple. Because oxygen utilization rates are difficul  相似文献   

Brokering Trust in Citizen Science     

Mat Gilfedder  James E. M. Watson  Thomas G. Campbell  Brian L. Sullivan  Hugh P. Possingham 《社会与自然资源》2019,32(3):292-302

Citizen science (CS) information requires systematic review that incorporates a range of interests and concerns. Yet, there has been little research on what might constitute reviewing best practice to ensure CS is trusted by contributors and users of the data. Insights from a survey of all 1134 reviewers who curate the global eBird Project highlight the knowledge-brokering work involved to ensure CS data are trusted by both citizens and science. Drawing on scholarship focused on key drivers of useable knowledge for natural resource decision-making, we consider CS reviewing best practice to ensure CS can be useful to the producers and users of this knowledge. We find that CS reviewers need to be motivated to provide appropriate feedback to improve CS data, commit to reviewing practice that is respected by citizens, and ensure the information published is credible and be reviewed by a supportive and accountable network of fellow reviewers.  相似文献   

Modelling the spatial dynamics of Mainland China-born migrants in Australia     

Siqin Wang  Thomas Sigler  Jonathan Corcoran  Yan Liu 《The Australian geographer》2019,50(2):201-219

Over the past two decades, migration from Mainland China (MC) to Australia has become increasingly significant. In contrast to previous migrant waves, post-2000 MC-born migrants in Australia are more likely to be highly skilled and/or financially independent, and often migrate under skilled, business and investment visa programs. Though scholarship has explored various facets of MC-born migrants’ settlement in Australian cities, the spatial dynamics of settlement, and change over time associated with these shifts in socio-economic profile, have remained unexplored. This paper draws on three census periods, and employs a local indicator of spatial autocorrelation together with a geographically weighted regression. We conclude that the settlement patterns of MC-born migrants in Australia do not follow the ‘straight-line’ assumptions of spatial assimilation theory, nor are they tied explicitly to socio-economic factors in the majority of capital cities. Instead, the settlement patterns of MC-born migrants vary by city: Sydney and Melbourne display the most spatially segmented settlement patterns; while Adelaide and Perth exhibit increasing levels of concentration as the number of MC-born migrants grows. Results indicate that while MC-born migrants are somewhat likely to cluster at the early stage of group formation, within-group spatial patterns are articulated by social attributes as the group grows in size and significance in a metropolitan context.  相似文献