Lunar motion: Theory and observations     

Jean Chapront  Michelle Chapront-Touzé 《Celestial Mechanics and Dynamical Astronomy》1996,66(1):31-38

Results of several fits of the lunar theory ELP 2000-82B and of Moons' theory of libration are presented. The theories are fitted both to JPL numerical integrations and to LLR observations  相似文献   

Origin of chaos in the Prometheus-Pandora system     

Peter Goldreich  Nicole Rappaport 《Icarus》2003,166(2):320-327

We demonstrate that the chaotic orbits of Prometheus and Pandora are due to interactions associated with the 121:118 mean motion resonance. Differential precession splits this resonance into a quartet of components equally spaced in frequency. Libration widths of the individual components exceed the splitting, resulting in resonance overlap which causes the chaos. Mean motions of Prometheus and Pandora wander chaotically in zones of width 1.8 and 3.1 deg yr⁻¹, respectively. A model with 1.5 degrees of freedom captures the essential features of the chaotic dynamics. We use it to show that the Lyapunov exponent of 0.3 yr⁻¹ arises because the critical argument of the dominant member of the resonant quartet makes approximately two separatrix crossings every 6.2 year precessional cycle.  相似文献   

Near-infrared constraints on the driving mechanisms for spiral structure     

Marc S. Seigar  Nicole E. Chorney  Phil A. James 《Monthly notices of the Royal Astronomical Society》2003,342(1):1-7

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TEM evidence for intracellular accumulation of lead by bacteria in subsurface environments     

Nicolas Perdrial  Nicole Liewig  Jean-Emmanuel Delphin  Franoise Elsass 《Chemical Geology》2008,253(3-4):196-204

We monitored near-surface atmospheric fallout (15-cm above ground) and soil solution (at 15, 35 and 55 cm below ground) derived nanoparticles over an 8-month period by collecting the particles directly onto TEM grids in anthropogenically-influenced (vineyard) and pristine (native forest) sites in France. Particle clusters trapped on the grid were selected randomly and individual particles were binned into eight different groups (euhedral clays, weathered clays, salts, oxi-hydroxides, bacteria, non-living organic matter, aggregates and undetermined). Bacteria represent 9–23% of the collected nanoparticle area (ave. 9.4% and 18% for two atmospheric collection sites and ave. 23% for soil infiltration samples). Bacteria were most often associated with non-living organic matter and comprised a variety of morpho-types. Interestingly, 45% of all the bacteria analyzed by transmission electron microscopy and electron dispersive spectroscopy (TEM-EDX) showed the presence of intracellular grains significantly enriched in lead and phosphorus. Intracellular sequestration of Pb into polyphosphate bodies has been observed in the laboratory, but this is the first observation of this phenomenon in a natural environment. Furthermore, this suggests that microbial-bound Pb may be an important transport mechanism in subsurface environments.  相似文献   

On the in situ aqueous alteration of soils on Mars     

Ronald Amundson  Stephanie Ewing  Brad Sutter  Oliver Chadwick  Michelle Walvoord 《Geochimica et cosmochimica acta》2008,72(15):3845-3864

Early (>3 Gy) wetter climate conditions on Mars have been proposed, and it is thus likely that pedogenic processes have occurred there at some point in the past. Soil and rock chemistry of the Martian landing sites were evaluated to test the hypothesis that in situ aqueous alteration and downward movement of solutes have been among the processes that have transformed these portions of the Mars regolith. A geochemical mass balance shows that Martian soils at three landing sites have lost significant quantities of major rock-forming elements and have gained elements that are likely present as soluble ions. The loss of elements is interpreted to have occurred during an earlier stage(s) of weathering that may have been accompanied by the downward transport of weathering products, and the salts are interpreted to be emplaced later in a drier Mars history. Chemical differences exist among the sites, indicating regional differences in soil composition. Shallow soil profile excavations at Gusev crater are consistent with late stage downward migration of salts, implying the presence of small amounts of liquid water even in relatively recent Martian history. While the mechanisms for chemical weathering and salt additions on Mars remain unclear, the soil chemistry appears to record a decline in leaching efficiency. A deep sedimentary exposure at Endurance crater contains complex depth profiles of SO₄, Cl, and Br, trends generally consistent with downward aqueous transport accompanied by drying. While no model for the origin of Martian soils can be fully constrained with the currently available data, a pedogenic origin is consistent with observed Martian geology and geochemistry, and provides a testable hypothesis that can be evaluated with present and future data from the Mars surface.  相似文献   

Assessment of spatial variation in carbon utilization by benthic and pelagic invertebrates in a temperate South African estuary using stable isotope signatures     

Nicole B. Richoux  P. William Froneman 《Estuarine, Coastal and Shelf Science》2007,71(3-4):545-558

Stable isotope analyses (δ¹³C and δ¹⁵N) were used to evaluate the spatial variations in carbon flow from primary producers to consumers at two sites in the temperate and permanently open Kariega Estuary on the southeastern coast of South Africa during October 2005 and February 2006. One site was located opposite a salt marsh while the second was upstream of the marsh. Except for significantly enriched δ¹³C values of Zostera capensis and surface sediments near the salt marsh, the δ¹³C and δ¹⁵N signatures of the producers were similar between sites. The invertebrates were clustered into groups roughly corresponding to the predominant feeding modes. The suspension feeders showed δ¹³C values closest to the seston, whereas the deposit feeders, detritivores and scavengers/predators had more enriched δ¹³C values reflecting primary carbon sources that were likely a combination of seston, Spartina maritima and Z. capensis at the upstream site, with an increased influence of benthic algae and Z. capensis at the salt marsh site. The δ¹⁵N signatures of the consumers showed a stepwise continuum rather than distinct levels of fractionation, indicating highly complex trophic linkages and significant dietary overlap among the species. Consumers exhibited significantly enriched δ¹³C values at the salt marsh site, an effect that was attributed to enriched Z. capensis detritus in this region in addition to increased phytoplankton biomass in their diets compared with invertebrates living upstream. The data reinforce the concept that between-site variations in the stable isotope ratios of consumers can result not only from dietary shifts, but also from alterations in the isotope ratios of primary producers.  相似文献   

Immediate profile and planform evolution of a beach nourishment project with hurricane influences   总被引：1，自引：0，他引：1  

Nicole A. Elko  Ping Wang 《Coastal Engineering》2007

In this study, planform adjustment began during a period of calm weather immediately after nourishment and then the passage of one strong storm caused a substantial portion of the total profile equilibration. Weekly beach profiles, shoreline surveys, and nearshore wave measurements were conducted before, during, and immediately after construction of the 1100-m long Upham Beach nourishment project on the low-energy, west coast of Florida. This project was constructed in three segments: the wide north segment, the central segment, and the narrow south segment. With the exception of the relatively distant passage of Hurricane Charley, calm weather prevailed for 45 days following completion of the south and central segments. Construction of the wide north segment was completed on August 27, 2004. Substantial planform diffusion occurred prior to construction completion via formation of a 300-m long spit extending from the wide north segment. The shoreline orientation was changed abruptly due to this diffusion spit formation, as opposed to the gradual adjustment predicted by most long-term models. Planform adjustment was initiated prior to profile equilibration, and it did not require high-energy conditions. A simple vector sum model for determining the orientation of a potential diffusion spit was developed. This study recommends designing end transitions at the predicted diffusion spit orientation to avoid post-nourishment spit formation during future projects.  相似文献   

Coastal Habitat Use and Residency of Juvenile Atlantic Sharpnose Sharks (Rhizoprionodon terraenovae)     

John K. Carlson  Michelle R. Heupel  Dana M. Bethea  Lisa D. Hollensead 《Estuaries and Coasts》2008,31(5):931-940

Coastal habitat use and residency of a coastal bay by juvenile Atlantic sharpnose sharks, Rhizoprionodon terraenovae, were examined by acoustic monitoring, gillnet sampling, and conventional tag–recapture. Acoustic monitoring data were used to define the residency and movement patterns of sharks within Crooked Island Sound, Florida. Over 3 years, sharks were monitored for periods of 1–37 days, with individuals regularly moving in and out of the study site. Individual sharks were continuously present within the study site for periods of 1–35 days. Patterns of movement could not be correlated with time of day. Home range sizes were typically small (average?=?1.29 km²) and did not vary on a yearly basis. Gillnet sampling revealed that juvenile Atlantic sharpnose sharks were present in all habitat types found within Crooked Island Sound, and peaks in abundance varied depending on month within a year. Although telemetry data showed that most individuals remained within the study site for short periods of time before emigrating, conventional tag–recapture data indicates some individuals return to Crooked Island Sound after extended absences (maximum length?=?1,352 days). Although conventional shark nursery theory suggests small sharks remain in shallow coastal waters to avoid predation, juvenile Atlantic sharpnose sharks frequently exited from protected areas and appear to move through deeper waters to adjacent coastal bays and estuaries. Given the high productivity exhibited by this species, the benefit gained through a nursery that reduces predation may be limited for this species.  相似文献   

The P-T-fO 2 stability of deerite,Fe 12 2+ Fe 6 3+ [Si12O40](OH)10     

Dominique Lattard  Nicole Le Breton 《Contributions to Mineralogy and Petrology》1994,115(4):474-487

New equilibrium experiments have been performed in the 20–27 kbar range to determine the upper thermal stability limit of endmember deerite, Fe ₁₂ ²⁺ Fe ₆ ³⁺ [Si₁₂O₄₀](OH)₁₀. In this pressure range, the maximum thermal stability limit is represented by the oxygen-conserving reaction: deerite(De)=9 ferrosilite(Fs)+3 magnetite(Mag)+3 quartz(Qtz)+5 H₂O(W) (1). Under the oxygen fugacities of the Ni-NiO buffer the breakdown-reduction reaction: De=12 Fs+2 Mag+5 W+1/2 O₂ (10) takes place at lower temperatures (e.g. T=63° at 27 kbar). The experimental brackets can be fitted using thermodynamic data for ferrosilite, magnetite and quartz from Berman (1988) and the following 1 bar, 298 K data for deerite (per gfw): V^o=55.74 J.bar^-1, S^o=1670 J.K^-1, H _f ^o =-18334 kJ, =2.5x10^-5K^-1, =-0.18x10^-5 bar^-1. Using these data in conjunction with literature data on coesite, grunerite, minnesotaite, and greenalite, the P-T stability field of endmember deerite has been calculated for P _s=P _{H 2}O. This field is limited by 6 univariant oxygenconserving dehydration curves, from which three have positive dP/dT slopes, the other three negative slopes. The lower pressure end of the stability field of endmember deerite is thus located at an invariant point at 250±70°C and 10+-1.5 kbar. Deerite rich in the endmember can thus appear only in environments with geothermal gradients lower than 10°C/km and at pressures higher than about 10 kbar, which is in agreement with 4 out of 5 independent P-T estimates for known occurrences. The presence of such deerite places good constraints on minimum pressure and maximum temperature conditions. From log f _{O 2}-T diagrams constructed with the same data base at different pressures, it appears that endmember deerite is, at temperatures near those of its upper stability limit, stable only over a narrow range of oxygen fugacities within the magnetite field. With decreasing temperatures, deerite becomes stable towards slightly higher oxygen fugacities but reaches the hematite field only at temperatures more than 200°C lower than the upper stability limit. This practically precludes the coexistence deerite-hematite with near-endmember deerite in natural environments.  相似文献   

Circumstellar dynamics and transfer     

Jean-Pierre J. Lafon  Nicole Berruyer 《Astrophysics and Space Science》1995,224(1-2):377-377

This paper is both a review and a presentation of new models. Observation and modelization of circumstellar envelopes of early type or late type stars are now quickly evolving because of new techniques and facilities for observations, and increased power of computers. More and more complex physical phenomena involved in mass driving can now be modelized, at many different size scales. While most of models were previously based on informations derived from spectrophotometric data only or on measurements concerning objects observed with no spatial resolution, observations at much increased angular resolution can provide constraints on models of these phenomena. Theory and modelization must take this new situation into account. Two approaches are possible and effectively used. On the one hand, dynamical/physical self consistent models can be built; on the other hand, elaborate semi-empirical models including complicated distributions of matter with asymmetries (3D models) can be built and fitted for direct comparison with results of High Angular Resolution Measurements. Adding such constraints to classical constraints leads to a new insight in the physics of circumstellar matter and, through it, of stellar and interstellar evolution. Two examples have been chosen, in which new models are presented and assuming or not spherical symmetry is carefully discussed:

?Circumstellar matter around evolved stars

?Shock waves propagating in the circumstellar matter around evolved stars.

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