An investigation of meteors in early April     

Terrance R. Arter  Iwan P. Williams 《Earth, Moon, and Planets》1995,68(1-3):141-153

In conducting a search through the IAU Meteor Catalogue at Lund, a peak in activity on April 8th, not corresponding to any known shower was discovered. Analysis of the orbit shows that a subset of those meteors originated on very coherent orbits. It is suggested that there could either represent a hither to unidentified stream or that they are meteoroids which, like the April Lyrids, were ejected from Comet Thatcher but have arrived onto their current orbits as a consequence primarily of Poynting - Robertson drag.  相似文献   

The Dynamics of Objects in the Inner Edgeworth–Kuiper Belt     

Daniel C. Jones  Iwan P. Williams  Mario D. Melita 《Earth, Moon, and Planets》2005,97(3-4):435-458

Objects in 3:2 mean motion resonance with Neptune are protected from close encounters with Neptune by the resonance. Bodies in orbits with semi-major axis between 39.5 and about 42 AU are not protected by the resonance; indeed due to overlapping secular resonances, the eccentricities of orbits in this region are driven up so that a close encounter with Neptune becomes inevitable. It is thus expected that such orbits are unstable. The list of known Trans-Neptunian objects shows a deficiency in the number of objects in this gap compared to the 43–50 AU region, but the gap is not empty. We numerically integrate models for the initial population in the gap, and also all known objects over the age of the Solar System to determine what fraction can survive. We find that this fraction is significantly less than the ratio of the population in the gap to that in the main belt, suggesting that some mechanism must exist to introduce new members into the gap. By looking at the evolution of the test body orbits, we also determine the manner in which they are lost. Though all have close encounters with Neptune, in most cases this does not lead to ejection from the Solar System, but rather to a reduced perihelion distance causing close encounters with some or all of the other giant planets before being eventually lost from the system, with Saturn appearing to be the cause of the ejection of most of the objects.  相似文献   

Geochemical Reference Sample Bibliography for 1990     

Iwan ROELANDTS 《Geostandards and Geoanalytical Research》1991,15(2):401-416

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Rainfall depth-duration-frequency curves and their uncertainties     

Aart Overeem  Adri Buishand  Iwan Holleman 《Journal of Hydrology》2008,348(1-2):124-134

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SECOND REPORT (1993) ON THE FIRST THREE GIT-IWG ROCK REFERENCE SAMPLES: ANORTHOSITE FROM GREENLAND, AN-G; BASALTE D'ESSEY-LA-CÔTE, BE-N; GRANITE DE BEAUVOIR, MA-N   总被引：1，自引：0，他引：1  

K. GOVINDARAJU  Iwan ROELANDTS 《Geostandards and Geoanalytical Research》1993,17(2):227-294

The first report (1980) on the three samples, Anorthosite AN-G, Basalt BE-N and Granite MA-N resulted in the chemical characterization of major, minor and 30 trace elements. The present report confirms the validity of a great majority of these working values, in addition to presenting working values for 20 more trace elements for each sample. Only compiled data on trace elements are presented, followed by Tables of statistical parameters used as a basis for their evaluation, both statistical and subjective. A plea is made to obtain more data on platinum group elements and on other "difficult" trace elements (Au, B, Bi, Se, Te, TI, …). The three samples have been processed in 900 kg amounts and, therefore, they are likely to remain available for some decades to come. As such, it is certainly worthwhile to take pains to characterize them well for even these difficult trace elements.  相似文献   

A linearization scheme for hysteretic systems subjected to random excitation     

Rudolf L. Grossmayer  Wilfred D. Iwan 《地震工程与结构动力学》1981,9(2):171-185

The problem of predicting the response of hysteretic yielding systems under random excitation is considered. The paper presents a linearization scheme which is motivated by extensive simulation studies of the bilinear hysteretic system. The response process is decomposed into a low frequency drift component and a component with a frequency near the linearized natural frequency of the system. Effective stiffness and damping parameters are presented. The accuracy of the various steps of the scheme is examined. The approach gives results which are in close agreement with simulation estimates even for large-system non-linearity.  相似文献   

The parent of the Quadrantid meteoroid stream     

Iwan P. Williams  & Collander-Brown 《Monthly notices of the Royal Astronomical Society》1998,294(1):127-138

The Quadrantid meteor shower is one of the major showers that produces reliable displays every January. However, it is unique amongst the major showers in still not having its parent uniquely identified. One of the reasons for this may be because the stream, and presumably the parent, lies in a region of the Solar system where near-resonant motion with Jupiter, coupled with potential close encounters, is possible. Such a combination can lead to a rapid dynamical evolution of an orbit. In particular, it may be possible that the orbit of the parent both satisfies the condition for a close encounter and is in resonant motion, while most of the meteoroids cannot satisfy both conditions. This results in the parent evolving away from the bulk of the stream.
To date, two suggestions have been made regarding possible parents for the Quadrantid stream, these being Comet 1491 I and Comet 96P/Machholz. The argument in favour of the first named being the parent is because of the general similarity between the orbits around 1491. The argument for comet 96P/Machholz being the parent is based on the similarity in orbital evolution coupled with a similarity in orbits phase-shifted by 2000 yr. In this paper we suggest that on both counts asteroid 5496 (1973 NA) is more similar to the Quadrantids, and that even if 5496 is not the actual parent in the strict sense that meteoroids are currently being ejected, it is either likely to be a fragment of the parent or the dormant remains of the parent.  相似文献   

1987 Compilation of Elemental Concentration Data for USGS BHVO-1, MAG-1, QLO-1, RGM-1, SCo-1, SDC-1, SGR-1 and STM-1   总被引：2，自引：0，他引：2  

Ernest S. GLADNEY  Iwan ROELANDTS 《Geostandards and Geoanalytical Research》1988,12(2):253-362

Elemental concentration data on up to 84 individual constituents in BHVO-1, MAG-1, QLO-1, RGM-1, SCo-1, SDC-1, SGR-1 and STM-1 have been collected from 311 journal articles and technical reports. These data are summarized in consensus (mean) values with uncertainties expressed as one standard deviation. Mean values are also calculated as a function of analytical procedure and all raw data are given in the tables.
Ce rapport rassemble des données analytiques parues dans 311 articles scientifiques ou rapports techniques sur 84 éléments dans huit échantillons du Service Géologique des Etats-Unis: BHVO-1, MAG-1, QLO-1, RGM-1, SCo-1, SDC-1, SGR-1 et STM-1. Quand cela a été possible, les valeurs de consensus (moyenne) sont présentées pour chaque élément avec l'incertitude exprimée en un écart-type. Des valeurs moyennes en fonction des procédures analytiques sont également présentées.  相似文献   

Geochemical Reference Sample Bibliography for 1987     

Iwan ROELANDTS 《Geostandards and Geoanalytical Research》1988,12(2):391-407

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Sequential Inductively Coupled Plasma Determination Of Some Rare-Earth Elements in Five French Geostandards   总被引：1，自引：0，他引：1  

Iwan ROELANDTS  Gilbert MICHEL 《Geostandards and Geoanalytical Research》1986,10(2):135-154

Experimental data for eleven rare-earth elements (REE) obtained by inductively coupled plasma spectrometry (ICP) in five French geochemical reference standards (BE-N, BR, DR-N, GS-N and FK-N)are presented. The method is based on acid digestion of the sample and cation-exchange separation from matrix elements.
Together with these new determinations an updated compilation of these reference materials are presented. Good agreement between the present results and previously preferred and published values obtained by various analytical techniques is observed. The values obtained in the present work corroborate the validity of the outlined method.  相似文献