Hill stability of satellite orbits     

V. V. Markellos  A. E. Roy 《Celestial Mechanics and Dynamical Astronomy》1981,23(3):269-275

Szebehely's criterion for Hill stability of satellites is derived from Hill's problem and a more exact result is obtained. Direct, Hill stable, circular satellites can exist almost twice as far from the planet as retrograde satellites. For direct satellites the new result agrees with Kuiper's empirical estimate that such satellites are stable up to a distance of half the radius of action of the planet. Comparison with the results of numerical experiments shows that Hill 'stability is valid for direct satellites but meaningless for retrograde satellites. Further accuracy for the maximum distance of Hill stable orbits is obtained from the restricted problem formulation. This provides estimates for planetary distances in double star systems.  相似文献   

Noble gases in the Allende and Abee meteorites and a gas-rich mineral fraction: investigation by stepwise heating     

B. Srinivasan  Roy S. Lewis  Edward Anders 《Geochimica et cosmochimica acta》1978,42(2):183-198

Noble gases in three meteoritic samples were examined by stepwise heating, in an attempt to relate peaks in the outgassing curves to specific minerals: NeKrXe in Allende (C3V) and an Allende residue insoluble in HF-HCl, and Xe in Abee (E4). In Allende, chromite and carbon contain most of the trapped Ne (²⁰Ne/²²Ne ≈ 8.7) and anomalous Xe enriched in light and heavy isotopes, and release it at ~850°C (bulk meteorite) or 1000°C (residue). Mineral Q, containing most of the trapped Ar, Kr, Xe as well as some Ne (²⁰Ne/²²Ne ≈ 10.4), releases its gases mainly between 1200 and 1600°C, well above the release temperatures of organic polymers (300–500°) or amorphous carbon (800–1000°). The high noble-gas release temperature, ready solubility in oxidizing acids, and correlation with acid-soluble Fe and Cr all point to an inorganic rather than carbonaceous nature of Q.All the radiogenic ¹²⁹Xe is contained in HCl, HF-soluble minerals, and is distributed as follows over the peaks in the release curve: Attend 1000° (75%), 1300° (25%); Abee (data of Hohenberg and Reynolds, 1969) ~850° (15%), 1100° (60%), 1300° (25%). No conclusive identifications of host phases can yet be given; possible candidates are troilite and silicates for Allende, and djerfisherite, troilite and silicates for Abee.Mineral Q strongly absorbs air xenon, and releases some of it only at 800–1000°C. Dilution by air Xe from Q and other minerals may explain why temperature fractions from bulk meteorites often contain less ^124–130Xe for a given enrichment in heavy isotopes than does xenon from etched chromitecarbon samples, although chromite-carbon is the source of the anomalous xenon in either case. Air xenon contamination thus is an important source of error in the derivation of fission xenon spectra.  相似文献   

Problems in relating the optical and X-ray emissions from a solar flare     

J.-René Roy 《Solar physics》1976,48(2):265-273

We evaluate the possibility that the short-lived Balmer line emission at H9 3835 Å of the 1972, August 2 (1839 UT) solar flare is due to heating of the chromosphere by bombarding electrons. We point out some of the problems of comparing the time behavior and spatial distribution of simultaneous hard and soft X-ray emissions. It is concluded that the present data do not justify the attribution of the short-lived optical emission to the presumed hard X-ray producing electrons.  相似文献   

A comparative error analysis of manual versus automated methods of data acquisition for algebraic strain estimation   总被引：1，自引：0，他引：1  

Kingshuk Roy Choudhury  Kieran Mulchrone   《Tectonophysics》2006,421(3-4):209-230

This paper presents a statistical analysis of the algebraic strain estimation algorithm of Shimamoto and Ikeda [Shimamoto, T., Ikeda, Y., 1976. A simple algebraic method for strain estimation from deformed eillipsoidal objects: 1. Basic theory. Tectonophysics 36, 315–337]. It is argued that the error in their strain estimation procedure can be quantified using an expected discrepancy measure. An analysis of this measure demonstrates that the error is inversely proportional to the number of clasts used. The paper also examines the role of measurement error, in particular that incurred under (i) a moment based and (ii) manual data acquisition methods. Detailed analysis of these two acquisition methods shows that in both cases, the effect of measurement error on the expected discrepancy is small relative to the effect of the sample size (number of objects). Given their relative speed advantage, this result favours the use of automated measurement methods even if they incur more measurement error on individual objects. Validation of these results is carried out by means of a simulation study, as well as by reference to studies appearing in previous literature. The results are also applied to obtain an upper bound on the error of strain estimation for various studies published in the literature on strain analysis.  相似文献   

Driving forces of tropical deforestation: The role of remote sensing and spatial models   总被引：2，自引：0，他引：2  

Rinku Roy Chowdhury 《Singapore journal of tropical geography》2006,27(1):82-101

Remote sensing technologies are increasingly used to monitor landscape change in many parts of the world. While the availability of extensive and timely imagery from various satellite sensors can aid in identifying the rates and patterns of deforestation, modelling techniques can evaluate the socioeconomic and biophysical forces driving deforestation processes. This paper briefly reviews some emerging spatial methodologies aimed at identifying driving forces of land use change and applies one such methodology to understand deforestation in Mexico. Satellite image classification, change analysis and econometric modelling are used to identify the rates, hotspots and drivers of deforestation in a case study of the southern Yucatán peninsular region, an enumerated global hotspot of biodiversity and tropical deforestation. In particular, the relative roles of biophysical and socioeconomic factors in driving regional deforestation rates are evaluated. Such methodological approaches can be applied to other regions of the forested tropics and contribute insights to conservation planning and policy.  相似文献   

Land use/land cover identification in an alpine and arid region (Nubra Valley, Ladakh) using satellite remote sensing     

P. K. Joshi  G. S. Rawat  H. Padaliya  P. S. Roy 《Journal of the Indian Society of Remote Sensing》2005,33(3):371-380

The remote sensing technology has been widely used for mapping the vegetation types in the tropical landscapes. However, in the temperate and alpine arid regions of India very few studies have been conducted using this technique. In the mountainous temperate arid conditions the vegetation is largely confined to marsh meadows, streams courses, river valleys and moist pockets close to snowfields. The ground truth collection in these zones are physically challenging due to tough terrain and restricted mobility. The detailed mapping of vegetation and other land use classes in these areas is therefore, extremely difficult. This paper describes the use of IRS-ID LISS III sensor for deciphering land cover details Nubra Valley, northern portion of Ladakh Autonomous Hill Council, Jammu & Kashmir (India). This analysis essentially emphasizes in bringing out various vegetation classes (speciallyHippophae rhamnoides and other medicinal plant communities) along the narrow river valleys.  相似文献   

La vallée d'Ys : un paléoréseau hydrographique immergé en baie de Douarnenez (Finistère,France)     

Gwénaël Jouet  Claude Augris  Bernard Hallegouët  Pascal Le Roy  Joël Rolet 《Comptes Rendus Geoscience》2003,335(5):487-494

Interpretation of the recent high-resolution survey, CANADOU 2000, in the Bay of Douarnenez (Finistère, France) allowed us to restore the morphology of the substratum and the sedimentary filling of the bay. The Brioverian and Palaeozoic substratum reveals a well-defined network of incised valleys as results of successive emergence stages of the Bay during the Quaternary. Valleys join in a westward-widened mean valley, called Ys Valley. The present-day sedimentary fill of the bay of Douarnenez appears mainly controlled by the Holocene rise and the consecutive highstand. It comprises fluvial and estuarine deposits filling up incised valleys and marine sedimentation extending out of the incised valleys. To cite this article: G. Jouet et al., C. R. Geoscience 335 (2003).To cite this article: G. Jouet et al., C. R. Geoscience 335 (2003).  相似文献   

Model Tests and Field Experiments for Fragmentation Assessment During Ringhole Blasting in BG Panels     

C. Sawmliana  P. Pal Roy  V. M. S. R. Murthy 《Fragblast: International Journal for Blasting and Fragmentation》2003,7(4):257-268

Experimental blasts were conducted in concrete blocks of known strengths to correlate field results in Blasting Gallery (BG) panels of GDK-10 Incline for improving fragmentation of coal to an optimum level so that blasted coal could easily be lifted totally by remote controlled LHDs and thereby mitigating the possibility of occurrence of spontaneous heating in BG districts before exhaustion of the panel. Various charge loading parameters and consequent breakage results were critically analyzed to arrive at a constructive conclusion, which could satisfactory improve the blast results.  相似文献   

Flood Damage Reduction Program (FDRP) in Québec: Case Study of the Chaudiére River     

Esther Roy  Jean Rousselle  Jacinthe Lacroix 《Natural Hazards》2003,28(2-3):387-405

This study presents the evolution of agreements between the governments of Canadaand Québec on flood damage reduction. In Québec, the implementation of a regulation about building in floodplains came about in 1983–1984. Today, this regulation takes the form of a policy called ``Policy of shores, littoral and floodplain protection'. Municipalities must adopt rules that concur with the principles of this policy.The Chaudiére River basin was selected for analysis of urban developmentduring the period following the application of building rules in flood-risk areas.Despite the ban on building in the strong current zone (0–20 year return periodflood zone), many buildings, essentially residential, have been erected in thiszone. These new constructions generally account for a low percentage of thetotal property value in the 0–100 year flooding area, but are legal since theyare connected to a water and sewage network that existed prior to the officialfloodplain regulation.Flood damage along the Chaudiére River will tend to increase for two reasons.Firstly, while respecting the policy mentioned above, sites are still available infloodplains for future development. Secondly, no structural flood protection workshave been erected in view of the fact they are only marginally profitable from anbenefit-cost point of view.  相似文献   

Re-Os Isotopic Measurements at the Femtomole Level in Natural Samples   总被引：17，自引：0，他引：17  

Jean Louis Birck  Matthieu Roy Barman  Françoise Capmas 《Geostandards and Geoanalytical Research》1997,21(1):19-27

Here we describe a new chemical separation method for Os and an improved mass spectrometric procedure for Re and Os. This technique is based on the selective extraction of OsO₄ from aqueous solution in liquid bromine. Among other advantages, this procedure avoids the cumbersome distillation procedure for Os and uses only commercial "off the shelf" PFA teflon labware. Blank levels for 0.5 g sample sizes are: 0.06 pg and 0.5 pg for Os and Re respectively. Samples containing as little as 1 pg g⁻¹ Os can be analysed reliably with this method. Adaptation to other dissolution methods is also discussed.  相似文献