Situations arise in celestial mechanics where orbital eccentricities are large and yet it is desirable to maintain the Darwin-Kaula Fourier decomposition of the perturbing function. Evaluation of the appropriate eccentricity functionsGlpq(e) requires a double summation which, for practical purposes, must be truncated. In this note criteria have been established for truncation of the expansion for eccentricities 0.75. 相似文献
The rotation of the inner core (IC) is influenced by the rest of the Earth through a number of coupling mechanisms. Among four possible coupling mechanisms, gravitational, pressure, viscous and electromagnetic, the first two torques are dominant. Numerous existing IC gravitational torque estimates have been shown to agree very well with one another Xu & Szeto 1996 ). It is shown in this paper that different estimates of the IC pressure torque are also in good agreement. The coupled rotation of the IC has been investigated in the frequency domain by several research groups (Mathews et al. 1991a,b; De Vries & Wahr 1991 ; Dehant et al. 1993; Jiang 1993 ). Not all of these efforts obtained two IC-related rotational modes, the inner-core wobble (ICW) and the free-inner-core nutation (FICN). We investigate this problem in the time domain and confirm the existence of the two modes. The periods of ICW and FICN are in good agreement with those obtained by other researchers. In studying the effects of coupling torques on the IC rotational modes we have found that depending on whether the IC net torque is 'restoring' or otherwise, an increased torque magnitude will respectively shorten or lengthen the ICW period. We have also found that the sense of FICN is determined by the orientation of the net coupling torque on the IC. 相似文献
This paper focuses on what observers have perceived to be a failure of development leading to a ‘crisis of youth’ as increasing numbers of young people find it more difficult to gain education, access to health, a job and meet standard of living aspirations. For some, a possible escape is offered by migration to Europe, the United States or Australia, often illegally. For those remaining behind, however, international development agencies offer a ‘globalisation of solutions’ to employment, gender inequality and poverty through the millennium development goals and the programmes to attain them. In this paper we do not take the failures of development at face value but look at local contexts to present a more complex picture of the relation between education, work and social life. Based on fieldwork conducted in urban areas of The Gambia and Ghana, we argue that rather than education as a catch-all solution we need to give more attention to the costs incurred by and for young people in pursuing education and training, to the operation of and actual opportunities in labour markets, and to patterns of gender socialisation which give women limited scope to exercise agency. This paper explores key gender dimensions of work and education among low-income urban youth noting that despite on-going efforts to increase young women’s enrolment in schools and access to employment, gender inequalities have been far from eradicated. Our field interviews reveal how social expectations that women should perform the bulk of reproductive labour in their youth as well as in adulthood and constraints placed on young women’s personal freedom in respect of their social relationships reduce time dedicated to education and establish fewer contacts relevant to securing paid employment. The result is for men to end up with more educational qualifications, more skills, and higher-paying jobs, even if unemployment among young people in general remains a major problem. 相似文献
A number of aquatic organisms have demonstrated an ability to modulate sediment deposition in tropical and temperate stream
systems, but little is known about the impact of similar benthic grazing processes in temperate pond systems. Using exclosure
experiments in mesocosms, we used tadpoles of the western toad (Anaxyrus boreas) to investigate two questions: (1) can grazing activities of tadpoles of the western toad in ponds reduce sediment accrual
on grazing surfaces (e.g. via bioturbation or ingestion); and (2) do these grazing activities contribute to enhanced periphyton
biomass and chlorophyll a content of benthic matter. Mesocosms received pulses of fine sediment weekly over 8 weeks to simulate allochthonous surface
inputs following rainstorms. Accumulated sediment and periphyton matter on exposed and grazing-restricted substrate surfaces
were measured weekly. Tadpole grazing activity significantly reduced the standing stock of periphyton on open grazing surfaces
by 80% in controls. Under sediment-additions, tadpoles effectively removed settled particulate matter from exposed grazing
surfaces, but no corresponding increase in periphyton biomass was observed. These results suggest that tadpoles can impact
the dynamics of sediment distribution in ponds as well as streams, providing support for a role as “ecosystem engineers” in
these habitats. 相似文献
The United States’ decision to withdraw from the Paris Agreement (pending possible re-engagement under different terms) may have significant ramifications for international climate policy, but the implications of this decision remain contested. This commentary illustrates how comparative analysis of US participation in multilateral environmental agreements can inform predictions and future assessments of the decision. We compare and contrast US non-participation in the Kyoto Protocol and the Paris Agreement, focusing on four key areas that may condition the influence of US treaty decisions on international climate policy: (i) global momentum on climate change mitigation; (ii) the possibility of US non-participation giving rise to alternative forms of international collaboration on climate policy; (iii) the timing and circumstances of the US decision to exit; and (iv) the influence of treaty design on countries’ incentives to participate and comply. We find that differences across the two treaties relating to the first three factors are more likely to reduce the negative ramifications of US withdrawal from the Paris Agreement compared to the Kyoto Protocol. However, the increased urgency of deep decarbonization renders US non-participation a major concern despite its declining share of global emissions. Moreover, key design features of the Paris Agreement suggest that other countries may react to the US decision by scaling back their levels of ambition and compliance, even if they remain in the Agreement.
Key policy insights
Increasing global momentum on mitigation since 1997 means that US withdrawal from the Paris Agreement is potentially less damaging than its non-participation in the Kyoto Protocol
Despite the declining US share of global emissions, greater urgency of deep decarbonization means that the non-participation of a major player, such as the US, remains problematic for global cooperation and achieving the Paris Agreement’s goals
Differences in the design of the Kyoto Protocol and Paris Agreement suggest that US non-participation is more likely to prompt reluctant countries to stay within the Paris framework but reduce levels of ambition and compliance, rather than exit the Agreement altogether
The Earth System Curator is a National Science Foundation sponsored project developing a metadata formalism for describing the digital resources used in climate simulations. The primary motivating observation of the project is that a simulation/model’s source code plus the configuration parameters required for a model run are a compact representation of the dataset generated when the model is executed. The end goal of the project is a convergence of models and data where both resources are accessed uniformly from a single registry. In this paper we review the current metadata landscape of the climate modeling community, present our work on developing a metadata formalism for describing climate models, and reflect on technical challenges we have faced that require new research in the area of Earth Science Informatics. 相似文献
Hydrous alteration of olivine macrocrysts in a Martian olivine phyric basalt, NWA 10416, and a terrestrial basalt from southern Colorado are examined using SEM, EPMA, TEM, and µXRD techniques. The olivines in the meteorite contain linear nanotubes of hydrous material, amorphous areas, and fluid dissolution textures quite distinct from alteration identified in other Martian meteorites. Instead, they bear resemblance to terrestrial deuteric alteration features. The presence of the hydrous alteration phase Mg‐laihunite within the olivines has been confirmed by µXRD analysis. The cores of the olivines in both Martian and terrestrial samples are overgrown by unaltered rims whose compositions match those of a separate population of groundmass olivines, suggesting that the core olivines are xenocrysts whose alteration preceded crystallization of the groundmass. The terrestrial sample is linked to deep crustal metasomatism and the “ignimbrite flare‐up” of the Oligocene epoch. The comparison of the two samples suggests the existence of an analogous relatively water‐rich magmatic reservoir on Mars. 相似文献