Analytical study of the swing-by maneuver in an elliptical system     

Alessandra F. S. Ferreira  Antônio F. B. A. Prado  Othon C. Winter  Denilson P. S. Santos 《Astrophysics and Space Science》2018,363(2):24

The objective of the present paper is to derive a set of analytical equations that describe a swing-by maneuver realized in a system of primaries that are in elliptical orbits. The goal is to calculate the variations of energy, velocity and angular momentum as a function of the usual basic parameters that describe the swing-by maneuver, as done before for the case of circular orbits. In elliptical orbits the velocity of the secondary body is no longer constant, as in the circular case, but it varies with the position of the secondary body in its orbit. As a consequence, the variations of energy, velocity and angular momentum become functions of the magnitude and the angle between the velocity vector of the secondary body and the line connecting the primaries. The “patched-conics” approach is used to obtain these equations. The configurations that result in maximum gains and losses of energy for the spacecraft are shown next, and a comparison between the results obtained using the analytical equations and numerical simulations are made to validate the method developed here.  相似文献   

2060 Chiron back to a minimum of brightness     

Daniela Lazzaro  Marcos A. Florczak  Alberto Betzler  Othon C. Winter  Silvia M. Giuliatti-Winter  Claudia A. Angeli  Dietmar W. Foryta 《Planetary and Space Science》1996,44(12):1547-1550

The results of photometric observations of comet/asteroid 2060 Chiron at the Observatório do Pico dos Dias (Brazil-OPD) and the Observatoire de Haute-Provence (France-OHP) during 1994 and 1995 are presented. The analysis of the data shows a decrease of 2060 Chiron brightness from its peak values of 1988–1991. The absolute magnitude, H_v, varies from a maximum of 6.6 in February 1994 up to a minimum of 6.8 in June 1995. Therefore 2060 Chiron is back to a minimum of activity close to that of 1983–1985. The slope parameter G is found to be G = 0.71 ± 0.15. It is suggested that the H-G magnitude system, generally adopted to present 2060 Chiron brightness, is not the most appropriate due to the cometary activity of this object.  相似文献   

Criticism of recent calculations of common envelope ejection     

Noam Soker  Amos Harpaz 《Monthly notices of the Royal Astronomical Society》2003,343(2):456-458

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Formation of saline groundwaters in the Baltic region through freezing of seawater during glacial periods   总被引：1，自引：0，他引：1  

Amos Bein  Arnon Arad 《Journal of Hydrology》1992,140(1-4):75-87

Typical Ca---Cl brines occur in crystalline and metamorphic rocks below freshwater horizons at various localities in Sweden and Finland. Total dissolved solids (TDS) range in concentration between 2 and 120 gl⁻¹ and have long been thought to derive from water-rock interactions. The relationships between Na, Cl and Br in these brines suggest, however, that they were derived from freezing of seawater during glacial periods. The brines were subsequently diluted by meteoric waters and their Ca/Mg ratio was increased through water-rock interactions in the subsurface. The hydrogeological model for both the formation of freeze-derived marine brines and their lateral intrusion involves restricted inland marine basins in recent and subrecent polar climatic belts. Seawater in such basins gradually freezes in response to glaciation. The solutes which concentrate in the remaining water body are residual after precipitation of a sequence of minerals which include carbonates, mirabilite and hydrohalite. Hydraulic pressure of the growing ice sheet over the frozen seas is gradually added to the ambient hydrostatic pressure exerted on the brines. This, together with their increased density, increases the intrusional potential of the brines. As the land ice cannot exert hydraulic pressure on continental groundwater in the aquifers, the balance of pressure favours deep landward intrusion of brines. Post-glacial processes cause the subsurface dilution and replacement of the brines both by seawater and fresh waters. The presence of such brines also far from present-day coastal settings reflects the shifting of coastlines as a result of isostatic movements and eustatic sea-level changes associated with glaciation and deglaciation.  相似文献   

First results from the North Iceland experiment     

C. Riedel  A. Tryggvason  B. Brandsdottír  T. Dahm  R. Stéfansson  M. Hensch  R. Böðvarsson  K. S. Vogfjord  S. Jakobsdottír  T. Eken  R. Herber  J. Holmjarn  M. Schnese  M. Thölen  B. Hofmann  B. Sigurdsson  S. Winter 《Marine Geophysical Researches》2006,27(4):267-281

Between June 2004 and September 2004 a temporary seismic network was installed on the northern insular shelf of Iceland and onshore in north Iceland. The seismic setup aimed at resolving the subsurface structure and, thus, the geodynamical transition from Icelandic crust to typical oceanic crust along Kolbeinsey Ridge. The experiment recorded about 1,000 earthquakes. The region encloses the Tjörnes Fracture Zone containing the Husavik–Flatey strike-slip fault and the extensional seismic Grimsey Lineament. Most of the seismicity occurs in swarms offshore. Preliminary results reveal typical mid-ocean crust north of Grimsey and a heterogeneous structure with major velocity anomalies along the seismic lineaments and north–south trending subsurface features. Complementary bathymetric mapping highlight numerous extrusion features along the Grimsey Lineament and Kolbeinsey Ridge. The seismic dataset promises to deliver new insights into the tectonic framework for earthquakes in an extensional transform zone along the global mid-ocean ridge system.  相似文献   

Spatial patterns of pollock and zooplankton distribution in the Pribilof Islands, Alaska nursery area and their relationship to pollock recruitment   总被引：2，自引：1，他引：2  

Swartzman  Gordon; Napp  Jeffrey; Brodeur  Richard; Winter  Andreas; Ciannelli  Lorenzo 《ICES Journal of Marine Science》2002,59(6):1167-1186

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Variations in age-0 pollock distribution among eastern Bering Sea nursery areas: A comparative study through acoustic indices     

A. Winter  K.O. Coyle  G. Swartzman 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2869

Cohort abundance of walleye pollock (Theragra chalcogramma) is subject to strong interannual variation in the eastern Bering Sea, and this variation is known to be determined largely at the age-0 stage. We estimated the spatial distributions and densities of age-0 walleye pollock in five nursery areas around the eastern Bering shelf in three successive years (1997–1999) from acoustic survey data. Concurrently, we calculated estimates of the spatial distribution of euphausiids, a major prey of age-0 walleye pollock, and estimates of spatial overlap of groundfish predators with the age-0 walleye pollock. The analyses showed that all nursery areas had low densities of age-0 walleye pollock in 1997, which ultimately produced the weakest adult year-class. In the intermediate year of 1998, age-0 densities were low to medium, and in 1999, which produced the strongest of the three adult year-classes, all nursery areas had medium to high age-0 walleye pollock densities. Euphausiid distributions had a consistently positive spatial relationship with age-0 walleye pollock. Groundfish predator density ratios were positively related to age-0 walleye pollock density when age-0 walleye pollock were displaced relatively northward. Our results suggest that abundance of age-0 walleye pollock, and hence of adult cohorts in the eastern Bering Sea, can be predictable from a concise set of indicators: the densities of age-0 walleye pollock at nursery areas in mid- to late-summer, their spatial relationship to euphausiids and groundfish predators, and the latitudinal trend of their distributions. The 3 years 1997–1999 had significant differences of physical conditions in the eastern Bering Sea, and represent an advantageous framework for testing these hypotheses.  相似文献   

Cloning of a chub metallothionein cDNA and development of competitive RT-PCR of chub metallothionein mRNA as a potential biomarker of heavy metal exposure   总被引：3，自引：0，他引：3  

Hayes RA  Regondi S  Winter MJ  Butler PJ  Agradi E  Taylor EW  Kevin Chipman J 《Marine environmental research》2004,58(2-5):665-669

Metallothionein has been assayed in a range of aquatic animal tissues as an indicator of metal exposure. We sequenced chub (Leuciscus cephalus) metallothionein cDNA which showed over 90% homology to common carp, goldfish and stone loach and 77% homology to rainbow trout sequences for metallothionein. We then used the extended primer method to develop an accurate quantitative competitive RT-PCR assay for metallothionein mRNA. RT-PCR was used to measure metallothionein mRNA in feral chub from a range of field sites, with different levels of heavy metal pollution, in the West Midlands, UK. Measurements were complemented by analysis of liver and gill metallothionein protein by capillary electrophoresis. There was no significant difference in the metallothionein protein levels between fish of different rivers and there was no evidence of elevation of mRNA at the sites of highest metal exposure. The level of metal exposure (e.g. zinc, nickel and cadmium each ranging between 15 and 28 microg/l ) at the pH (7.5-8.5) of these rivers appears insufficient to elevate hepatic or gill metallothionein in chub. A lack of elevation of hepatic metallothionein mRNA in chub exposed to zinc, copper and manganese for 24 h and 10 days in the laboratory also suggests a non-responsiveness of this species.  相似文献   

Effects of crustacean traps on benthic fauna     

Eno  N. Clare; MacDonald  David S.; Kinnear  Jim A. M.; Amos  S. Chris; Chapman  Colin J.; Clark  Robin A.; Bunker  Francis St P.D.; Munro  Colin 《ICES Journal of Marine Science》2001,58(1):11-20

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“Coastal dynamics and human impact: south-eastern North Sea”, an overview     

Christian Winter  Alexander Bartholomä 《Geo-Marine Letters》2006,26(5):303-303

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