The arrangement in mean elements space of the periodic orbits close to that of the Moon     

G. B. Valsecchi  E. Perozzi  A. E. Roy  B. A. Steves 《Celestial Mechanics and Dynamical Astronomy》1993,56(1-2):373-380

In a simplified model of the Earth-Moon-Sun system based on the restricted circular 3-dimensional 3-body problem, it is possible to find numerically a set of 8 periodic orbits whose time evolutions closely resemble that of the Moon's orbit. These orbits have a period of 223 synodic months (i.e. the period of the Saros cycle known for more than two millennia as a means of predicting eclipses), and are characterized by a secular rotation of the argument of perigee . Periodic orbits of longer durations exhibiting this last feature are very abundant in Earth-Moon-Sun dynamical models. Their arrangement in the space of the mean orbital elements- for various values of the lunar mean motion is presented.  相似文献   

Inductive electric fields in the magnetosphere     

M. Roy  Ramaswamy Rajaram 《Planetary and Space Science》1979,27(6):817-819

A quantitative estimate of the electric fields induced by the time dependent ring current is made incorporating the drifts and induced electric fields in a self-consistent manner. It has been shown that in the ring current region, the results of the self-consistent calculations deviate substantially from the first order estimates hitherto obtained. Since for a rapidly varying ring current, the induced electric field can be of the same order as the convection electric field in the magnetosphere, these deviations have to be taken into account in substorm studies.  相似文献   

The north-south distribution of major solar flare events,sunspot magnetic classes and sunspot areas (1955–1974)     

Roy  J. -René 《Solar physics》1977,52(1):53-61

The north-south incidence has been studied of 31 white-light flares observed since 1859 and of 1669 events meeting the criteria for major flares of Dodson and Hedeman (1971) for the period 1955–1974. The asymmetry in favor of the northern hemisphere increases strikingly with the importance of the events. Similarly, magnetically complex sunspot groups (Mt. Wilson classes, and) display a more pronounced asymmetry in favor of the north than non-complex groups for 1962–1970. Contrary to the flare asymmetry, the spottedness asymmetry is independent of the size of sunspots.  相似文献   

Water in India with reference to agriculture and population: some issues and patterns —dynamic approaches needed for development     

Roy BK 《GeoJournal》1990,20(3):271-284

In this paper an attempt is made to present some facets of status of water for agriculture and population in India. The issues are basic in nature which have been focused by scholars all over time and again. The materials are gathered from various sources to highlight and to consider a plea in the context of population-hydrological regions of the country to develop water potentials. Some characteristic mapping has also been conducted showing the main parameters of water utilization, need and spatial issues regarding consumptive use of water during agricultural operations as per the seasons prevalent in India. A relation is also established with the drought areas leading to assess the need for water. The human problems specially in relation to the safe drinking water is also projected in relation to distributional qualities with reference to natural regions by districts. The study does not claim a full assessment of the water issue due to paucity of statistics on water use, generation and potentials but it does indicate in many ways the geographical problems as an important study for further research by all concerned.  相似文献   

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   

Structural architecture of a highly oblique divergent plate boundary segment   总被引：1，自引：0，他引：1  

Amy E. Clifton  Simon A. Kattenhorn 《Tectonophysics》2006,419(1-4):27-40

The Reykjanes Peninsula in southwest Iceland is a highly oblique spreading segment of the Mid-Atlantic Ridge oriented about 30° from the direction of absolute plate motion. We present a complete and spatially accurate map of fractures for the Reykjanes Peninsula with a level of detail previously unattained. Our map reveals a variability in the pattern of normal, oblique- and strike-slip faults and open fractures which reflects both temporal and spatial strain partitioning within the plate boundary zone. Fracture density varies across the length and width of the peninsula, with density maxima at the ends and at the northern margin of the zone of volcanic activity. Fractures with similar strike cluster into distinct structural domains which can be related to patterns of faulting predicted for oblique extension and to their spatial distribution with respect to volcanic fissure swarms. Additional structural complexity on the Reykjanes Peninsula can be reconciled with magmatic periodicity and associated temporal strain partitioning implied by GPS data, as well as locally perturbed stress fields. Individual faults show variable slip histories, indicating that they may be active during both magmatic and amagmatic periods associated with different strain fields.  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